1st year Chemistry

Class 9 Mathematics Unit 1: Real Numbers Exercise 1.1 Solutions with Tips

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Looking for detailed solutions for Class 9 Mathematics, Unit 1: Real Numbers Exercise 1.1? This guide provides clear explanations, step-by-step solutions, and helpful tips for solving problems on rational and irrational numbers, properties, and number line representation. Perfect for CBSE and NCERT students! and all boards of punjab

Question 1: Identify as rational or irrational

Solutions:
(i) 2.353535→ Rational (repeating decimal)
(ii) 0.6‾ → Rational (repeating decimal)
(iii) 2.236067… → Irrational (non-terminating, non-repeating decimal; it’s 5
(iv) √7 → Irrational (not a perfect square)
(v) e → Irrational (Euler’s number is irrational)
(vi) π → Irrational (value of π\pi is non-terminating and non-repeating)
(vii) 5+√11 → Irrational (irrational part √11)
(viii) √3+√13 → Irrational (sum of two irrationals)
(ix) 15/4→ Rational (fraction of integers)
(x) (2−√2)(2+√2)→ Rational (product simplifies to 22−√(2)2=4−2=2)

Tips for Identifying Rational and Irrational Numbers:

  1. Rational Numbers: Can be expressed as a fraction p/q, where p,q are integers and q≠0. Includes terminating and repeating decimals.
  2. Irrational Numbers: Cannot be expressed as a fraction. Examples: √2,π,e.

Question 2: Represent numbers on the number line

Steps to Plot the Numbers: (i) √2: Approximate 2≈1.41. Locate 1.41 on the number line.
(ii) √3}: Approximate √3≈1.73. Locate 1.73.
(iii) 4 1/3: Convert to improper fraction 13/3≈4.33 . Locate 4.33.
(iv) −1/7: Locate just slightly left of 0 (approx. -0.14).
(v) 5/8 : Approximate 5/8=0.625. Locate 0.625.
(vi) 2 3/4 : Convert to improper fraction 11/4≈2.75. Locate 2.75.

Tips for Plotting on the Number Line:

  1. Approximate square roots and fractions to decimals for accurate placement.
  2. Use a ruler to mark equal divisions on the number line for precision.

Question 3: Express repeating decimals as rational numbers

Solutions: (i) 0.4‾: Let x=0.4‾.
Multiply by 10: 10x=4.4‾.
Subtract: 10x−x=4.4‾−0.4‾.
9x=4, so x=4/9.

(ii) 0.37‾: Let x=0.37‾.
Multiply by 100: 100x=37.37‾.
Subtract: 100x−x=37.37‾−0.37‾
99x=37, so x=37/99x.

(iii) 0.21‾: Let x=0.21‾.
Multiply by 100: 100x=21.21‾
Subtract: 100x−x=21.21‾−0.21‾
99x=21, so x=21/99=7/33

Tips for Converting Repeating Decimals:

  1. Identify the repeating part and assign the decimal to x.
  2. Multiply x by powers of 10 to shift the decimal point.
  3. Subtract the equations to eliminate the repeating part and solve for x.

Question 4: Name the property used

Solutions:
(i) (a+4)+b=a+(4+b): Associative Property of Addition
(ii) √2+√3=√3+√2: Commutative Property of Addition
(iii) x−x=0 : Existence of Additive Inverse
(iv) a(b+c)=ab+ac : Distributive Property
(v) 16+0=16: Existence of Additive Identity
(vi) 100×1=100: Existence of Multiplicative Identity
(vii) 4×(5×8)=(4×5)×8: Associative Property of Multiplication
(viii) ab=ba Commutative Property of Multiplication

Tips to Remember Properties:

  1. Commutative: Order doesn’t matter (e.g., a+b=b+a, ab=ba).
  2. Associative: Grouping doesn’t matter (e.g., (a+b)+c=a+(b+c).
  3. Distributive: Multiplication distributes over addition (e.g., a(b+c)=ab+ac.
  4. Identity: Adding 0 or multiplying by 1 keeps the number unchanged.
  5. Inverse: Adding the opposite or multiplying by the reciprocal gives a neutral result (e.g., x−x=0).

Question 5: Name the property used

Solutions:
(i) −3<−1  ⟹  0<2: Transitive Property of Inequality
(ii) If a<b, then 1/a>1/b: Reciprocal Property of Inequality
(iii) If a<b, then a+c<b+c: Addition Property of Inequality
(iv) If ac<bc and c>0, then a<b: Multiplication Property of Inequality (for c>0)
(v) If ac<bc and c<0, then a>b: Multiplication Property of Inequality (for c<0)
(vi) Either a>b or a=b or a<b : Trichotomy Law

Tips to Solve Inequalities:

  1. Reciprocal Inequality: Reverses when reciprocals are taken (for positive numbers).
  2. Multiplication Rule: Inequality flips if multiplied/divided by a negative number.
  3. Transitive Property: If a<b and b<c , then a<c.

Question 6: Insert two rational numbers

Solutions:
(i) Between 1/3 and 1/4:

  • Find a common denominator: 1/3=4/12 = , 1/4=3/12.
  • Insert fractions like 10/36 and 11/36.

(ii) Between 33 and 44:

  • Choose decimals like 3.2 and 3.8.

(iii) Between 3/5 and 4/5:

  • Insert 7/10 and 9/10.

Tips for Inserting Rational Numbers:

  1. Convert fractions to a common denominator for clarity.
  2. Use decimals for whole numbers and simple fractions for fractions.
  3. Always choose values between the given numbers.

Logical Problems Practice Questions with Answers for MDCAT, UHS

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Prepare effectively for MDCAT, UHS, and GIKI entrance exams with our curated logical problems practice questions. This resource is designed to enhance your logical reasoning abilities, providing challenging problems and solutions that help you develop the skills necessary for success in these competitive exams. Whether you are aiming for medical school or a place in GIKI, our carefully selected set of logical problems will guide you through key concepts, ensuring you’re well-prepared for test day. Master logical reasoning with this collection of practice questions and answers.

MCQ 1:

Premises:

  1. All cats are animals.
  2. All animals are living beings.

Conclusions:

  1. All cats are living beings.
  2. All living beings are cats.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: A

MCQ 2:

Premises:

  1. All books are knowledge sources.
  2. All knowledge sources are useful.

Conclusions:

  1. All books are useful.
  2. Some useful things are books.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 3:

Premises:

  1. All flowers are plants.
  2. All plants need water.

Conclusions:

  1. All flowers need water.
  2. Some plants are flowers.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 4:

Premises:

  1. All cars are vehicles.
  2. All vehicles have wheels.

Conclusions:

  1. All cars have wheels.
  2. All wheels are parts of vehicles.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: A

MCQ 5:

Premises:

  1. All humans are mammals.
  2. All mammals are warm-blooded.

Conclusions:

  1. All humans are warm-blooded.
  2. All warm-blooded beings are humans.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: A

MCQ 6:

Premises:

  1. All stars are celestial objects.
  2. All celestial objects emit light.

Conclusions:

  1. All stars emit light.
  2. Some celestial objects are stars.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 7:

Premises:

  1. All teachers are professionals.
  2. All professionals are educated.

Conclusions:

  1. All teachers are educated.
  2. Some educated people are professionals.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 8:

Premises:

  1. All triangles are polygons.
  2. All polygons have sides.

Conclusions:

  1. All triangles have sides.
  2. All sides are part of triangles.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: A

MCQ 9:

Premises:

  1. All fruits are food.
  2. All apples are fruits.

Conclusions:

  1. All apples are food.
  2. Some food items are fruits.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 10:

Premises:

  1. All squares are rectangles.
  2. All rectangles are quadrilaterals.

Conclusions:

  1. All squares are quadrilaterals.
  2. Some quadrilaterals are rectangles.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 11:

Premises:

  1. All engineers are professionals.
  2. All professionals need skills.

Conclusions:

  1. All engineers need skills.
  2. Some skilled people are professionals.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 12:

Premises:

  1. All birds have wings.
  2. All sparrows are birds.

Conclusions:

  1. All sparrows have wings.
  2. All winged creatures are sparrows.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: A

MCQ 13:

Premises:

  1. All cities have roads.
  2. All capitals are cities.

Conclusions:

  1. All capitals have roads.
  2. Some cities are capitals.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 14:

Premises:

  1. All cars are machines.
  2. All machines require maintenance.

Conclusions:

  1. All cars require maintenance.
  2. Some machines are cars.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 15:

Premises:

  1. All pencils are stationary items.
  2. All stationary items are used in schools.

Conclusions:

  1. All pencils are used in schools.
  2. Some school items are pencils.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 16:

Premises:

  1. All poets are writers.
  2. All writers have imagination.

Conclusions:

  1. All poets have imagination.
  2. Some writers are poets.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 17:

Premises:

  1. All circles are shapes.
  2. All shapes have boundaries.

Conclusions:

  1. All circles have boundaries.
  2. Some shapes are circles.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 18:

Premises:

  1. All dogs are mammals.
  2. All mammals breathe air.

Conclusions:

  1. All dogs breathe air.
  2. All air-breathing creatures are mammals.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: A

MCQ 19:

Premises:

  1. All plants are living things.
  2. All living things need water.

Conclusions:

  1. All plants need water.
  2. Some living things are plants.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 20:

Premises:

  1. All mountains are landforms.
  2. All landforms are part of Earth.

Conclusions:

  1. All mountains are part of Earth.
  2. Some parts of Earth are landforms.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 21:

Premises:

  1. All birds are animals.
  2. All penguins are birds.

Conclusions:

  1. All penguins are animals.
  2. Some animals are penguins.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 22:

Premises:

  1. All phones are electronic devices.
  2. All electronic devices need power.

Conclusions:

  1. All phones need power.
  2. Some power-consuming devices are phones.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 23:

Premises:

  1. All squares are parallelograms.
  2. All parallelograms have diagonals.

Conclusions:

  1. All squares have diagonals.
  2. Some parallelograms are squares.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 24:

Premises:

  1. All oceans are water bodies.
  2. All water bodies support life.

Conclusions:

  1. All oceans support life.
  2. Some water bodies are oceans.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 25:

Premises:

  1. All musicians are artists.
  2. All guitarists are musicians.

Conclusions:

  1. All guitarists are artists.
  2. Some artists are musicians.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 26:

Premises:

  1. All fishes are aquatic animals.
  2. All aquatic animals live in water.

Conclusions:

  1. All fishes live in water.
  2. Some aquatic animals are fishes.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 27:

Premises:

  1. All chairs are furniture.
  2. All furniture is made of materials.

Conclusions:

  1. All chairs are made of materials.
  2. Some materials are used for furniture.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Both conclusions follow.
D. Neither conclusion follows.

Correct Answer: C

MCQ 28:

Premises:

  1. All dogs are mammals.
  2. All mammals are vertebrates.
  3. All vertebrates have a backbone.

Conclusions:

  1. All dogs have a backbone.
  2. All mammals are dogs.
  3. Some vertebrates are mammals.

Options:
A. Only conclusion 1 follows.
B. Only conclusions 1 and 3 follow.
C. Only conclusion 2 follows.
D. All conclusions follow.

Correct Answer: B

MCQ 29:

Premises:

  1. All flowers are plants.
  2. All plants require sunlight.
  3. All things that require sunlight perform photosynthesis.

Conclusions:

  1. All flowers perform photosynthesis.
  2. Some plants are flowers.
  3. All things that perform photosynthesis are flowers.

Options:
A. Only conclusion 1 follows.
B. Only conclusions 1 and 2 follow.
C. Only conclusion 3 follows.
D. All conclusions follow.

Correct Answer: B

MCQ 30:

Premises:

  1. All books are knowledge sources.
  2. All knowledge sources are valuable.
  3. Some valuable things are rare.

Conclusions:

  1. All books are valuable.
  2. Some books are rare.
  3. Some rare things are books.

Options:
A. Only conclusion 1 follows.
B. Only conclusion 2 follows.
C. Only conclusions 1 and 3 follow.
D. All conclusions follow.

Correct Answer: A

MCQ 31:

Premises:

  1. All teachers are educators.
  2. All educators are knowledgeable.
  3. All knowledgeable people are respected.

Conclusions:

  1. All teachers are respected.
  2. All respected people are teachers.
  3. Some knowledgeable people are educators.

Options:
A. Only conclusion 1 follows.
B. Only conclusions 1 and 3 follow.
C. Only conclusion 2 follows.
D. All conclusions follow.

Correct Answer: B

MCQ 32:

Premises:

  1. All rivers flow into the sea.
  2. All seas contain saltwater.
  3. Some saltwater bodies are oceans.

Conclusions:

  1. All rivers flow into saltwater bodies.
  2. Some oceans are seas.
  3. Some saltwater bodies are rivers.

Options:
A. Only conclusion 1 follows.
B. Only conclusions 1 and 3 follow.
C. Only conclusion 2 follows.
D. All conclusions follow.

Correct Answer: A

MCQ 33:

Premises:

  1. All cats are mammals.
  2. All mammals are warm-blooded.
  3. Some warm-blooded animals are carnivores.

Conclusions:

  1. All cats are warm-blooded.
  2. Some carnivores are cats.
  3. Some warm-blooded animals are cats.

Options:
A. Only conclusion 1 follows.
B. Only conclusions 1 and 3 follow.
C. Only conclusions 2 and 3 follow.
D. All conclusions follow.

Correct Answer: B

MCQ 34:

Premises:

  1. All planets revolve around a star.
  2. All stars emit light.
  3. Some light-emitting objects are visible from Earth.

Conclusions:

  1. All planets revolve around light-emitting objects.
  2. Some visible objects are stars.
  3. All visible objects are planets.

Options:
A. Only conclusion 1 follows.
B. Only conclusions 1 and 2 follow.
C. Only conclusion 2 follows.
D. All conclusions follow.

Correct Answer: A

MCQ 35:

Premises:

  1. All students are learners.
  2. All learners seek knowledge.
  3. Some knowledge seekers are researchers.

Conclusions:

  1. All students seek knowledge.
  2. Some researchers are students.
  3. Some knowledge seekers are students.

Options:
A. Only conclusion 1 follows.
B. Only conclusions 1 and 3 follow.
C. Only conclusions 2 and 3 follow.
D. All conclusions follow.

Correct Answer: A

MCQ 36:

Premises:

  1. All clouds contain water vapor.
  2. All water vapor forms droplets under cold conditions.
  3. Some droplets create rain.

Conclusions:

  1. All clouds can form droplets under cold conditions.
  2. Some rain is caused by clouds.
  3. All water vapor is found in clouds.

Options:
A. Only conclusion 1 follows.
B. Only conclusions 1 and 2 follow.
C. Only conclusion 3 follows.
D. All conclusions follow.

Correct Answer: A

MCQ 37:

Premises:

  1. All birds lay eggs.
  2. All eggs contain nutrients.
  3. Some nutrients are essential for life.

Conclusions:

  1. All birds produce nutrients.
  2. Some life-essential nutrients come from eggs.
  3. Some birds are essential for life.

Options:
A. Only conclusion 1 follows.
B. Only conclusions 1 and 2 follow.
C. Only conclusion 2 follows.
D. All conclusions follow.

Correct Answer: A

MCQ 38:

Premises:

  1. All fruits have seeds.
  2. All seeds grow into plants.
  3. Some plants provide food.

Conclusions:

  1. All fruits can grow into plants.
  2. Some plants come from fruits.
  3. Some fruits provide food.

Options:
A. Only conclusion 1 follows.
B. Only conclusions 1 and 2 follow.
C. Only conclusions 2 and 3 follow.
D. All conclusions follow.

Correct Answer: B

MCQ 39:

Premises:

  1. All squares are rectangles.
  2. All rectangles have four sides.
  3. Some four-sided shapes are rhombuses.

Conclusions:

  1. All squares have four sides.
  2. Some rhombuses are rectangles.
  3. All rectangles are squares.

Options:
A. Only conclusion 1 follows.
B. Only conclusions 1 and 2 follow.
C. Only conclusion 2 follows.
D. None of the conclusions follow.

Correct Answer: A

MCQ 40:

Premises:

  1. All metals are elements.
  2. All elements are part of the periodic table.
  3. Some elements are gases.

Conclusions:

  1. All metals are part of the periodic table.
  2. Some elements are metals.
  3. All gases are elements.

Options:
A. Only conclusion 1 follows.
B. Only conclusions 1 and 2 follow.
C. Only conclusion 3 follows.
D. All conclusions follow.

Correct Answer: B

Start your own business created by Artificial Intelligence

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Discover the latest business roles created by advancements in artificial intelligence. From AI engineers to data strategists, explore how AI is shaping the future of work across industries.

Artificial intelligence (AI) is reshaping industries and creating a variety of new opportunities across diverse sectors. Here are some examples of roles emerging due to advancements in AI:

1. AI-Specific Roles

  • AI/ML Engineer: Develops machine learning models, algorithms, and AI systems.
  • Data Scientist: Extracts insights and builds models using large datasets.
  • AI Ethics Specialist: Ensures AI systems adhere to ethical standards and minimize bias.
  • AI Trainer: Annotates and trains AI systems, particularly for applications like natural language processing or image recognition.
  • Prompt Engineer: Designs effective prompts to optimize AI model outputs.

2. Data-Related Roles

  • Data Labeler: Prepares and annotates datasets for training AI models.
  • Big Data Engineer: Manages and structures large-scale datasets used for AI applications.
  • Data Strategist: Identifies ways to leverage AI-driven insights for business growth.

3. AI Deployment and Integration

  • AI Solution Architect: Designs frameworks to integrate AI solutions into existing systems.
  • Automation Specialist: Identifies processes for automation and implements AI-powered workflows.
  • AI Product Manager: Oversees the development and deployment of AI-enabled products.

4. Creative and Content Roles

  • AI-Enhanced Content Creator: Utilizes AI tools to generate, optimize, or edit multimedia content.
  • AI Art Specialist: Collaborates with AI tools to create innovative art, animations, or designs.
  • Voice Synthesis Specialist: Develops custom voice solutions using AI-generated voices.

5. Human-AI Interaction Roles

  • Human-AI Interaction Designer: Designs user experiences and interfaces for AI applications.
  • Conversational AI Designer: Creates effective dialogues and flows for chatbots and virtual assistants.
  • AI Relationship Manager: Bridges gaps between AI teams and clients to ensure smooth implementation.

6. Legal and Regulatory Roles

  • AI Policy Advisor: Guides organizations on compliance with AI regulations and standards.
  • AI Legal Specialist: Navigates intellectual property, liability, and data protection issues related to AI.
  • Regulatory Compliance Officer: Ensures adherence to laws governing AI usage.

7. Industry-Specific Roles

  • AI in Healthcare:
    • AI Diagnostics Specialist
    • Personalized Treatment Advisor
  • AI in Finance:
    • Fraud Detection Analyst
    • Algorithmic Trading Specialist
  • AI in Retail:
    • Personalization Strategist
    • Supply Chain Optimizer

8. Maintenance and Support Roles

  • AI System Monitor: Monitors AI systems for performance, accuracy, and errors.
  • AI Support Specialist: Troubleshoots AI-related issues for end-users.
  • Model Maintenance Engineer: Updates and retrains AI models to ensure continued relevance.

9. Education and Training Roles

  • AI Educator/Trainer: Teaches AI skills and tools to professionals and students.
  • AI Curriculum Developer: Creates learning programs focused on AI technologies.

10. AI Entrepreneurship

  • AI Startup Founder: Identifies gaps in the market and builds innovative AI-driven solutions.
  • AI Consultant: Advises businesses on AI strategy and implementation.

Laboratory and practical skills chapter 13 9th class new syllabus

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Learn essential laboratory safety measures for handling hazardous chemicals, preventing accidents, and responding to emergencies. Explore tips, precautions, and detailed procedures to ensure a safe working environment.

(i) Safety in the chemistry laboratory is:

  • Correct Answer: (d) a shared responsibility
  • Explanation: Safety in a chemistry lab requires all parties—students, professors, and lab in-charges—to collaborate and follow proper safety protocols. It ensures mutual accountability and reduces the risk of accidents.
  • Tip: Always assume collective responsibility for safety in shared environments.

(ii) Accidents often result from:

  • Correct Answer: (d) all of the above
  • Explanation: Accidents are typically caused by a combination of mistakes, lack of common sense, and failure to follow instructions. Awareness and adherence to guidelines can prevent most mishaps.
  • Tip: Develop the habit of reading instructions thoroughly and staying alert in practical environments.

(iii) The label “Warning” on a chemical bottle signifies:

  • Correct Answer: (c) that the user should be careful when using the chemical
  • Explanation: A “Warning” label indicates a moderate level of hazard, requiring careful handling to avoid harm. It is less severe than “Danger” but still demands caution.
  • Tip: Familiarize yourself with standard chemical hazard labels (e.g., Warning, Danger, Caution) and their meanings.

(iv) The label “Corrosive” on a chemical bottle indicates:

  • Correct Answer: (c) that the contact destroys living tissue
  • Explanation: Corrosive substances can cause severe damage to skin, eyes, and other tissues upon contact. Proper handling, including wearing gloves and protective equipment, is essential.
  • Tip: Always use personal protective equipment (PPE) when handling corrosive chemicals.

(v) Example of a highly toxic chemical:

  • Correct Answer: (c) Potassium Cyanide
  • Explanation: Potassium cyanide is highly toxic and can be fatal even in small amounts. Ethanol, acetic acid, and potassium permanganate are not as acutely toxic.
  • Tip: Recognize high-risk chemicals and understand their toxicity levels to handle them appropriately.

(vi) Example of self-reactive chemical:

  • Correct Answer: (c) Picric acid
  • Explanation: Picric acid is a self-reactive chemical that can become explosive under certain conditions. Phenol, potassium, and n-Hexane do not exhibit self-reactive behavior.
  • Tip: Store self-reactive chemicals under recommended conditions to prevent accidents.

(vii) When diluting an acid with water:

  • Correct Answer: (c) always add acid to water
  • Explanation: Adding water to acid can cause a violent reaction, leading to splattering and potential burns. To dilute acid safely, always add the acid slowly to water while stirring.
  • Tip: Remember the phrase “AAA”—Always Add Acid (to water).

(viii) What should you do in case of a fire drill in the lab?

  • Correct Answer: (c) close gas valves and turn off all equipment
  • Explanation: During a fire drill, ensuring that all sources of potential hazards (like gas and electrical equipment) are secured helps prevent accidents and ensures safety.
  • Tip: Follow the lab’s fire evacuation protocol and stay calm during drills.

Short Answer Questions:

  1. Name some corrosive chemicals.
    • Examples: Hydrochloric acid (HCl), Sulfuric acid (H₂SO₄), Sodium hydroxide (NaOH).
  2. What type of safety precautions are adopted to avoid damage due to explosive chemicals?
    • Use small quantities.
    • Store them in cool, dry conditions.
    • Avoid friction, heat, and impact near explosive chemicals.
  3. What type of damages can reactive chemicals cause?
    • Reactive chemicals can cause explosions, fires, toxic gas release, or damage to equipment and surroundings.
  4. Indicate two such safety instructions that are required to avoid radiation.
    • Wear lead aprons or shields.
    • Limit exposure time and maintain a safe distance from the radiation source.
  5. Which chemicals can cause suffocation?
    • Examples: Carbon monoxide (CO), Hydrogen sulfide (H₂S), Chlorine gas (Cl₂).
  6. Why are signs and symbols posted on lab and chemical bottles?
    • To alert users of potential hazards.
    • To ensure proper handling, storage, and disposal of chemicals.
  7. How should fire caused by chemicals be handled?
    • Use appropriate fire extinguishers (e.g., CO₂ for electrical fires, Class D for metal fires).
    • Avoid using water if it reacts with the chemical.
  8. Why are emergency drills important to face emergency situations?
    • They prepare individuals to respond effectively in real emergencies.
    • They reduce panic and ensure timely evacuation or intervention.

3. Constructed Response Questions

i. How will you handle an emergency situation caused by fire due to short-circuiting?

  • Response:
    1. Turn off the main power supply: Immediately cut off the electricity to stop the source of the short-circuiting.
    2. Activate fire alarm: Alert everyone in the vicinity of the fire.
    3. Use appropriate fire extinguishers: For electrical fires, use a Class C or CO₂ extinguisher. Do not use water as it conducts electricity.
    4. Evacuate the area: Ensure all individuals leave the premises in an orderly fashion.
    5. Call emergency services: Contact fire services and provide details about the fire and the lab layout.
    6. Contain the fire if safe: Close doors to prevent the spread of smoke or fire but ensure personal safety.

ii. What type of reactions should be carried out in a fume cupboard?

  • Response:
    1. Volatile Reactions: Reactions that release harmful vapors, such as ammonia or chlorine gas.
    2. Toxic Reactions: Processes involving toxic chemicals like hydrogen sulfide or formaldehyde.
    3. Combustible Reactions: Reactions producing flammable gases or involving volatile solvents.
    4. Highly Reactive Chemicals: Reactions involving exothermic processes or potentially explosive compounds.

iii. Put forward at least two suggestions to improve safety in the lab.

  • Response:
    1. Implement regular safety training: Educate lab personnel and students on handling chemicals, equipment, and emergency situations.
    2. Upgrade safety equipment: Ensure fire extinguishers, first-aid kits, and personal protective equipment (PPE) are easily accessible and regularly maintained.

iv. Can you identify warning symbols posted for radiation and asphyxiant chemicals?

  • Response:
    • Radiation Symbol: A trefoil symbol with three curved blades radiating from a central circle, typically yellow and black.
    • Asphyxiant Symbol: There isn’t a universal asphyxiant symbol, but gases like nitrogen and carbon dioxide are often marked with hazard symbols indicating gas under pressure or health hazard.

v. Why do sudden shocks cause some chemicals to explode?

  • Response:
    Sudden shocks or impacts can destabilize unstable chemical bonds in reactive substances, such as explosives (e.g., TNT, nitroglycerin). This causes rapid decomposition, releasing a large amount of energy in the form of heat, light, and pressure waves, leading to an explosion.

4. Descriptive Questions

i. Explain hazards due to explosive and toxic chemicals.

  • Response:
    Explosive chemicals can cause significant physical damage, injuries, and even fatalities due to high-pressure shockwaves, flying debris, and heat. Toxic chemicals pose risks such as poisoning, respiratory issues, skin burns, and long-term health effects like organ damage or cancer.

ii. Write down five common safety instructions used to avoid all types of hazards.

  • Response:
    1. Always wear appropriate PPE, including gloves, goggles, and lab coats.
    2. Never eat or drink in the laboratory.
    3. Store chemicals in labeled containers and according to their hazard class.
    4. Dispose of waste according to environmental regulations.
    5. Familiarize yourself with the location and usage of safety equipment, such as fire extinguishers and eyewash stations.

iii. Explain the importance of warning signs and symbols to avoid any accident in the lab.

  • Response:
    Warning signs and symbols communicate vital safety information at a glance. They alert users to potential hazards, such as flammable materials, toxic gases, corrosive substances, or radiation. This helps in preventing accidents by guiding proper handling and storage.

iv. Name some toxic chemicals. Describe the effects of spreading toxic gas in the lab.

  • Response:
    Examples of toxic chemicals include chlorine gas, ammonia, carbon monoxide, and hydrogen cyanide. If a toxic gas spreads in the lab, it can cause respiratory distress, poisoning, and even death. It may also contaminate surfaces and equipment, leading to long-term risks.

v. A student has spilled over a corrosive and explosive chemical due to an accident. Which emergency measures will you take to tackle the situation?

  • Response:
    1. Evacuate the area: Ensure everyone moves to a safe distance.
    2. Wear appropriate PPE: Protect yourself before addressing the spill.
    3. Neutralize the spill: Use neutralizing agents recommended for the chemical (e.g., sodium bicarbonate for acids).
    4. Ventilate the area: Turn on fume hoods and exhaust systems to disperse fumes.
    5. Contact emergency services: Inform the lab supervisor and hazardous material response team.

5. Investigative Question

i. A tanker carrying poisonous chlorine gas leaked, causing an accident in Lahore. Provide proposals to avoid such accidents in the future.

  • Response:
    1. Regular Maintenance: Conduct frequent inspections and maintenance of transport vehicles.
    2. Training: Train drivers and staff in handling hazardous materials and responding to emergencies.
    3. Route Planning: Use low-population density routes for transporting toxic chemicals.
    4. Monitoring Systems: Install gas leak detectors and tracking systems on tankers.
    5. Emergency Response Protocols: Establish well-equipped response teams and evacuation plans for areas along the route.

Empirical Data Collection and Analysis: A Comprehensive Guide chapter 12

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Empirical data collection and analysis form the backbone of evidence-based research. This guide covers step-by-step methods, real-world examples, and tools to gather and interpret data effectively. Ideal for researchers, students, and professionals aiming for accuracy and reliability in their studies.

Question (i):

Statement: Which of the following pairs of quantities may be measured in the same unit?
Options:
(a) Heat and temperature
(b) Temperature and area
(c) Heat and work
(d) Length and work

Correct Answer: (c) Heat and work

Explanation:
Heat and work are both forms of energy and are measured in joules (J) in the SI system.

Tips and Tricks:

  • Always link the units to the physical quantities: energy is measured in joules.
  • Remember that temperature is measured in kelvin (K), and length is measured in meters (m).

Question (ii):

Statement: In which unit we usually measure the energy present in food?
Options:
(a) Kilojoules
(b) Megajoules
(c) Calorie
(d) Joule

Correct Answer: (c) Calorie

Explanation:
The energy in food is commonly measured in calories or kilocalories, though joules can also be used.

Tips and Tricks:

  • Remember: 1 calorie = 4.184 joules.
  • Energy in food is rarely represented in kilojoules for daily usage.

Question (iii):

Statement: What prefix is used for 1012?
Options:
(a) Mega
(b) Pico
(c) Giga
(d) Tera

Correct Answer: (d) Tera

Explanation:
Giga is the prefix for 109, and Tera is the prefix for 1012. The question might have a typo in choices.

Tips and Tricks:

  • Memorize the SI prefixes:
    • 106: Mega
    • 109: Giga
    • 1012: Tera

Question (iv):

Statement: In SI, the unit of pressure is expressed in:
Options:
(a) Newton per metre
(b) Newton per metre square
(c) Joule
(d) Pascal

Correct Answer: (d) Pascal

Explanation:
Pressure is force per unit area. In SI, pressure is measured in pascals (Pa), where 1 Pa=1 N/m2

  • Remember: Pressure=Force/Area

Question (v):

Statement: Which symbol is used for kilogram in SI units?
Options:
(a) K
(b) k
(c) kgm
(d) kg

Correct Answer: (d) kg

Explanation:
The SI unit of mass is the kilogram, denoted by “kg.”

Tips and Tricks:

  • Avoid confusion with “K,” which is for kelvin (temperature).

Question (vi):

Statement: What does a mole represent?
Options:
(a) Number
(b) Mass
(c) Volume
(d) Length

Correct Answer: (a) Number

Explanation:
A mole represents 6.022×1023 (Avogadro’s number). It is a measure of quantity, not mass, volume, or length.

Tips and Tricks:

  • Recall Avogadro’s number when dealing with moles.

Question (vii):

Statement: Which unit of volume should usually be used in chemistry?
Options:
(a) Millilitre
(b) Litre
(c) Cubic centimetre
(d) Cubic metre

Correct Answer: (c) Cubic centimetre

Explanation:
In chemistry, small volumes are often measured in cubic centimeters (cm³), which are equivalent to millilitres (mL).

Tips and Tricks:

  • Remember that 1 cm3=1 mL

Question (viii):

Statement: Express 0.00008400.0000840 in scientific notation:
Options:
(a) 8.40×10−3
(b) 8.40×10−4
(c) 8.40×10−5
(d) 7.40×10−4

Correct Answer: (c) 8.40×10−5

Explanation:
To convert to scientific notation:

  • Move the decimal 5 places to the right, so 0.0000840=8.40×10−5

Tips and Tricks:

  • Count the decimal places to determine the exponent.

Question (ix):

Statement: In SI, the prefix “nano” means:
Options:
(a) 103
(b) 10−6
(c) 10−9
(d) 1012

Correct Answer: (c) 10−9

Explanation:
Nano is the SI prefix for 10−9

Tips and Tricks:

  • Memorize prefixes: micro (10−6), nano (10−9), pico (10−12)

Question (x):

Statement: 65∘Cis equivalent to:
Options:
(a) 85∘F
(b) 149∘F
(c) 180∘F
(d) −85∘F

Correct Answer: (b) 149∘F

Explanation:
Use the formula: ∘F=(∘C×95)+32

Substituting 65∘C

∘F=(65×95)+32=149∘F

Tips and Tricks:

  • Remember the conversion formula for Celsius to Fahrenheit.

2. Questions for Short Answers

(i) What is consistency of results?
Answer:
Consistency of results means getting the same result when an experiment or measurement is repeated under the same conditions.

(ii) Why SI units are user-friendly?
Answer:
SI units are user-friendly because they are based on a decimal system, making calculations easier and more standardized worldwide.

(iii) Does systematic error affect accuracy?
Answer:
Yes, systematic errors affect accuracy because they cause measurements to consistently differ from the true value.

(iv) What is the reason behind a random error?
Answer:
Random errors occur due to unpredictable factors like slight changes in environmental conditions or limitations of measuring instruments.

(v) What is the difference between precision and accuracy?
Answer:

  • Accuracy: How close a measurement is to the true value.
  • Precision: How consistent repeated measurements are, even if they are not close to the true value.

(vi) Which other systems of measurements are used apart from SI units?
Answer:
Other systems include the Imperial System (used in the USA) and the CGS System (centimetre, gram, second).

(vii) Define metre.
Answer:
A metre is the SI unit of length, defined as the distance light travels in 1/299,792,4581/299,792,458 seconds in a vacuum.

(viii) Mention two benefits scientists get by using SI units.
Answer:

  1. SI units are used worldwide, making data and results easy to compare.
  2. They are based on fixed standards, ensuring accuracy and reliability.

3. Constructed Response Questions

(i) Compare the units in SI system with those in MKS system.
Answer:
The SI system includes all MKS units (metre, kilogram, second) but also adds more units for quantities like temperature (kelvin) and electric current (ampere). SI is a broader and more complete system.

(ii) What are five basic SI units used in chemistry?
Answer:

  1. Metre (m) – for length
  2. Kilogram (kg) – for mass
  3. Second (s) – for time
  4. Mole (mol) – for amount of substance
  5. Kelvin (K) – for temperature

(iii) Explain the three units derived for basic SI units.
Answer:

  1. Newton (N): Derived for force (1 N=1 kg⋅m/s2
  2. Pascal (Pa): Derived for pressure (1 Pa=1 N/m2
  3. Joule (J): Derived for energy (1 J=1 N⋅m1

(iv) Why do we prefer to use smaller units of mass and volume in chemistry?
Answer:
In chemistry, substances are measured in very small quantities. Using smaller units like grams (g) or millilitres (mL) makes the measurements easier and more practical.

(v) What difficulties do we expect to encounter if we use different units of measurement in daily life?
Answer:
Using different units can lead to confusion, incorrect calculations, and errors when converting between systems.

4. Descriptive Questions

(i) What are our indigenous units of measurement for mass, volume, and length?
Answer:

  • Mass: Maund, seer
  • Volume: Litre, pail
  • Length: Cubit, hand span

(ii) Compare SI units with Imperial system of units.
Answer:

  • SI units are based on the decimal system, while Imperial units are not.
  • Example:
    • SI unit of length is metre; Imperial unit is feet.
    • SI unit of mass is kilogram; Imperial unit is pound.

(iii) How can you avoid systematic errors in your measurements?
Answer:

  • Calibrate instruments properly.
  • Avoid faulty equipment.
  • Use proper measurement techniques.

(iv) How do taking measurements in SI units ensure safety and reliability?
Answer:
SI units are accurate and universally accepted, reducing chances of errors in measurements, which is crucial for safety and reliability in science and engineering.

(v) Can a student be both inaccurate and imprecise in his measurements?
Answer:
Yes, a student can be both inaccurate (far from the true value) and imprecise (measurements are inconsistent). This happens when both the method and tools used are incorrect.

5. Investigative Question

Elaborate the importance of using SI units in space exploration.
Answer:
Using SI units in space exploration is important because:

  1. They ensure uniformity in calculations and measurements across different countries and space agencies.
  2. SI units reduce the risk of errors in crucial missions where precision is vital.
  3. They simplify the sharing of data and collaboration in international projects.

Chapter 11: Hydrocarbons Exercise- 9th Class (Punjab & Lahore Board)

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Find detailed solutions for Chapter 11 “Hydrocarbons” from the 9th Class Chemistry syllabus. Designed for Punjab Boards and Lahore Board, this guide covers alkanes, alkenes, alkynes, and their applications with step-by-step explanations.

Q1: Which other atom is almost always present along with carbon atoms in all organic compounds?

Options:
(a) Oxygen
(b) Nitrogen
(c) Hydrogen
(d) Halogen

Correct Answer: (c) Hydrogen

Explanation:
Hydrogen is almost always bonded to carbon atoms in organic compounds because it helps satisfy the valency of carbon, forming stable molecules.

Tip: Remember that carbon-hydrogen bonds are the backbone of organic chemistry.

Q2: Which other metal can be used to reduce alkyl halides?

Options:
(a) Al
(b) Mg
(c) Ni
(d) Co

Correct Answer: (b) Mg

Explanation:
Grignard reagents are formed when alkyl halides react with magnesium in dry ether, which is a reduction process.

Tip: Magnesium is crucial for the preparation of organometallic compounds like Grignard reagents.

Q3: If n-heptane undergoes a combustion reaction, what products do you expect to form?

Options:
(a) Alkanes
(b) Alkenes
(c) CO₂ and H₂O
(d) Both alkanes and alkenes

Correct Answer: (c) CO₂ and H₂O

Explanation:
Combustion of hydrocarbons like n-heptane always produces carbon dioxide and water in the presence of excess oxygen.

Tip: Hydrocarbon + Oxygen → CO₂ + H₂O (Exothermic Reaction).

Q4: Why does a mixture of zinc and hydrochloric acid act as a reducing agent?

Options:
(a) Because zinc acts as a reducing agent.
(b) Because atomic hydrogen is produced with Zn/HCl which acts as a reducing agent.
(c) Because molecular hydrogen is produced with Zn/HCl which acts as a reducing agent.
(d) Because chloride ions are produced with Zn/HCl which act as a reducing agent.

Correct Answer: (b) Because atomic hydrogen is produced with Zn/HCl which acts as a reducing agent.

Explanation:
Zinc reacts with HCl to produce hydrogen gas, which in its atomic form is a strong reducing agent.

Tip: Think about how atomic hydrogen is more reactive than molecular hydrogen.

Q5: Which alkane will evolve the most amount of heat when it is burnt with oxygen?

Options:
(a) Ethane
(b) Propane
(c) Butane
(d) Iso-butane

Correct Answer: (c) Butane

Explanation:
The heat evolved in combustion depends on the number of carbon and hydrogen atoms in the alkane. Butane has more C-H bonds, leading to higher energy release.

Tip: Longer chain alkanes release more energy upon combustion.

Q6: Indicate the most reactive hydrocarbon.

Options:
(a) CH≡CH
(b) CH₂=CH₂
(c) CH₃-CH₃
(d) CH₃-CH₂-CH₃

Correct Answer: (a) CH≡CH

Explanation:
Acetylene (CH≡CH) has a triple bond, which is more reactive compared to single and double bonds because of the high energy stored in the triple bond.

Tip: Reactivity order: Triple bond > Double bond > Single bond.

Q7: Which hydrocarbon is responsible for explosions in coal mines?

Options:
(a) Butane
(b) Pentane
(c) Methane
(d) Ethene

Correct Answer: (c) Methane

Explanation:
Methane (CH₄), also called “firedamp,” is a primary cause of explosions in coal mines due to its flammable nature and the formation of explosive mixtures with air.

Tip: Methane-air mixtures are dangerous; always associate methane with safety risks in mining.

Q8: Which product will be formed when ethyl bromide (C₂H₅Br) is treated with Zn/HCl?

Options:
(a) CH₄
(b) C₂H₆
(c) CH₃-CH₂-CH₂-CH₃
(d) CH₃-CH₃

Correct Answer: (b) C₂H₆

Explanation:
Ethyl bromide undergoes reduction with Zn/HCl to produce ethane (C₂H₆).

Tip: Alkyl halides reduce to the corresponding alkane when treated with Zn/HCl.

Multiple-Choice Questions (MCQs)

  1. Which of the following is not a process of halogenation of alkanes?
    • (a) Cracking
    • (b) Chlorination
    • (c) Bromination
    • (d) Iodination
    Answer: (a) Cracking
  2. How many moles of oxygen will be required to completely burn propane?
    • (a) 4 moles
    • (b) 5 moles
    • (c) 3 moles
    • (d) 6 moles
    Answer: (b) 5 moles

Questions for Short Answers

  1. Differentiate between an organic and an inorganic compound.
    Answer: Organic compounds contain carbon and hydrogen, while inorganic compounds typically do not contain both carbon and hydrogen.
  2. Why are organic compounds found in large numbers?
    Answer: Carbon atoms can form stable chains and rings, allowing a vast variety of structures and compounds.
  3. Name the products which are obtained when natural gas is oxidized under controlled conditions.
    Answer: Carbon dioxide, water, and heat energy are produced.
  4. How is the naphtha fraction decomposed to give lower hydrocarbons?
    Answer: By cracking, where larger hydrocarbon molecules are broken down into smaller ones using heat or a catalyst.
  5. Write the molecular formula, structural formula, and condensed structural formula for iso-butane.
    Answer:
    • Molecular formula: C4H10
structural formula of isobutane
  1. How are organic compounds useful for us?
    Answer: They are used as fuels, medicines, plastics, and in many industrial and household applications.
  2. Write down the names of five organic compounds that exist naturally.
    Answer: Methane, glucose, ethanol, acetic acid, and citric acid.
  3. Give the IUPAC name of the compound:
    Structure: CH3-CH(CH3)-CH2-CH3
    Answer: 2-Methylbutane
  4. How do the melting and boiling points of alkanes change when we move from lower members to higher members?
    Answer: The melting and boiling points increase as the molecular weight increases due to stronger van der Waals forces.

Constructed Response Questions

  1. Why do alkanes show little reactivity towards other reagents?
    Answer: Alkanes have strong C-C and C-H bonds and are non-polar, making them chemically stable and less reactive.
  2. Why does a mixture of natural gas and air explode?
    Answer: The mixture forms a highly combustible combination. When ignited, it releases energy rapidly, causing an explosion.
  3. How do you compare the melting and boiling points of inorganic and organic compounds?
    Answer: Organic compounds generally have lower melting and boiling points compared to inorganic compounds due to weaker intermolecular forces.
  4. Reactions of alkanes with chlorine take place in the presence of sunlight. What is the role of sunlight in the reaction?
    Answer: Sunlight provides energy to break the chlorine molecule (Cl2) into reactive chlorine radicals, initiating the reaction.
  5. How do you compare the boiling point of n-butane with that of iso-butane?
    Answer: n-Butane has a higher boiling point than iso-butane due to its linear structure, which allows stronger van der Waals forces compared to the branched structure of iso-butane.
  6. Why are organic compounds not generally soluble in water?
    Answer: Organic compounds are non-polar, while water is polar. Due to the “like dissolves like” principle, non-polar substances do not dissolve well in polar solvents like water.

Descriptive Questions

  1. Describe the importance of organic compounds in daily life.
    Answer: Organic compounds are essential in our lives. They are found in food, clothing (cotton, wool, polyester), fuels (petrol, diesel, natural gas), medicines, plastics, cosmetics, and more. They form the basis of modern life.
  2. Why is carbon so important as an element that the whole branch of chemistry is based on it?
    Answer: Carbon is unique due to its ability to form stable covalent bonds with other carbon atoms, leading to long chains and complex structures. This versatility makes it the foundation of organic chemistry.
  3. A carbon-carbon single bond (C-C) does not behave as a functional group but a carbon-carbon double bond (C=C) does. Explain.
    Answer: A single C-C bond is non-reactive and does not impart specific chemical properties, while a double C=C bond is reactive and contributes to the reactivity of molecules, making it a functional group.
  4. Explain the IUPAC system of nomenclature for alkanes.
    Answer: The IUPAC naming system involves:
    • Identifying the longest continuous carbon chain as the parent hydrocarbon.
    • Numbering the chain to give substituents the lowest possible numbers.
    • Naming and arranging substituents alphabetically.
    • Using prefixes (e.g., di-, tri-) for multiple identical substituents.
  5. How is the combustion reaction of alkanes useful for us?
    Answer: Combustion of alkanes releases energy in the form of heat and light. It is used for generating power, cooking, heating, and running vehicles.

Investigative Questions

  1. When the natural gas valve is kept open in the kitchen, the gas spreads through the whole kitchen. This may cause an explosion. What is the reason for this explosion, and how can you avoid it?
    Answer:
    • Reason: Natural gas is highly flammable. When mixed with air, it forms an explosive mixture that ignites upon encountering a spark or flame.
    • Prevention: Always ensure the gas valve is turned off after use. Regularly check for leaks and ensure proper ventilation in the kitchen.
  2. Neem is a common tree grown throughout our country. Comment on the medicinal benefits of this tree.
    Answer: Neem has antibacterial, antifungal, and anti-inflammatory properties. It is used in traditional medicine to treat skin conditions, boost immunity, and act as a natural pesticide.
  3. Name a few popular medicines which are, in fact, organic compounds.
    Answer: Aspirin, paracetamol, ibuprofen, penicillin, and vitamins like vitamin C are all organic compounds used in medicine.

Chapter 10: Environmental Chemistry – 9th Class New Syllabus (Punjab Boards & Lahore Board)

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Explore Chapter 10 “Environmental Chemistry” from the 9th Class new syllabus for Punjab Boards and Lahore Board. Understand air pollution, greenhouse effect, acid rain, and strategies to protect the environment with easy-to-learn explanations.

Multiple Choice Questions

(i) Which gases are responsible for the greenhouse effect?
Options:
(a) SO₂, NO
(b) CO₂, CO
(c) CO₂, CH₄
(d) O₂, O₃
Correct Answer: (c) CO₂, CH₄
Explanation: Carbon dioxide (CO₂) and methane (CH₄) are major greenhouse gases that trap heat in the Earth’s atmosphere, leading to the greenhouse effect.
Tip: Always associate greenhouse gases with their ability to trap heat (e.g., CO₂, CH₄, N₂O). Gases like O₂ and O₃ don’t significantly contribute to this effect.

(ii) Indicate the source of sulfur which is responsible for the presence of oxides of sulfur in the atmosphere.
Options:
(a) Decomposition of vegetation
(b) Waste gases from digestion of animals
(c) Photochemical smog
(d) Combustion of fossil fuels
Correct Answer: (d) Combustion of fossil fuels
Explanation: Burning fossil fuels (coal, oil, etc.) releases sulfur dioxide (SO₂) and other sulfur oxides into the atmosphere.
Tip: Think of industrial processes and power plants as key contributors to sulfur pollution.

(iii) Concentration of which gas in the atmosphere is decreased by photosynthesis in plants?
Options:
(a) Oxygen
(b) Nitrogen
(c) Carbon dioxide
(d) Water vapor
Correct Answer: (c) Carbon dioxide
Explanation: Plants absorb CO₂ during photosynthesis to produce oxygen and glucose.
Tip: Photosynthesis reduces CO₂, not oxygen or water vapor, in the environment.

(iv) Which substance remains unaffected in the catalytic converter fixed in the exhaust of automobiles?
Options:
(a) CO₂
(b) CO
(c) NO
(d) NO₂
Correct Answer: (a) CO₂
Explanation: Catalytic converters reduce pollutants like CO, NO, and hydrocarbons but do not affect CO₂, which is not harmful in small amounts.
Tip: Remember that catalytic converters aim to reduce harmful emissions but allow CO₂ to pass through.

(v) People of which age groups are the most affected by air pollution?
Options:
(a) Young adults
(b) Cancer patients
(c) Children
(d) Both children and aged people
Correct Answer: (d) Both children and aged people
Explanation: Children and the elderly have weaker immune and respiratory systems, making them more vulnerable to air pollution.
Tip: When asked about susceptibility, think of the most physically vulnerable groups (young and old).

(vi) In which area there is a greater possibility of acid rain?
Options:
(a) Around villages
(b) Around big cities
(c) Around industrial areas
(d) Around water bodies
Correct Answer: (c) Around industrial areas
Explanation: Industrial areas release large amounts of sulfur dioxide (SO₂) and nitrogen oxides (NOₓ), which cause acid rain when mixed with water in the atmosphere.
Tip: Acid rain is linked to industrial emissions, so look for industrial-related options.

(vii) Why is smog not felt in summer?
Options:
(a) Because fog is not present in summer
(b) Because due to heat of the earth the smoke rises up
(c) Because in summer smoke and fog cannot mix with each other
(d) Because less fossil fuels are burnt in summer
Correct Answer: (b) Because due to heat of the earth the smoke rises up
Explanation: In summer, higher temperatures cause pollutants to rise higher into the atmosphere, reducing the formation of smog near the ground.
Tip: Smog is more common in winter due to temperature inversion.

(viii) Which catalyst is used in the catalytic converter fixed in the exhaust systems of automobiles?
Options:
(a) Ni
(b) Cu
(c) Pt, Pd and Rh
(d) CaO
Correct Answer: (c) Pt, Pd and Rh
Explanation: Platinum (Pt), Palladium (Pd), and Rhodium (Rh) are used in catalytic converters to reduce harmful vehicle emissions.
Tip: Remember the precious metals (Pt, Pd, Rh) for catalytic converters.

(ix) Which components are essential for the formation of photochemical smog?
Options:
(a) CO, NO₂, CO₂
(b) NO₂, volatile organic compounds, sunlight
(c) CO₂, NO₂, sunlight
(d) Volatile organic compounds, NO₂, CO
Correct Answer: (b) NO₂, volatile organic compounds, sunlight
Explanation: Photochemical smog forms when sunlight reacts with nitrogen oxides (NOₓ) and volatile organic compounds (VOCs).
Tip: Photochemical smog always involves sunlight, NO₂, and VOCs.

(x) Which air pollutant can cause respiratory problems?
Options:
(a) CO₂
(b) Ozone
(c) Smog
(d) CO
Correct Answer: (c) Smog
Explanation: Smog contains harmful pollutants like particulate matter and ground-level ozone, which irritate the respiratory system.
Tip: Respiratory issues are typically associated with smog or particulate pollutants.

Short Questions

1. What is the main objective of environmental education?
To make people aware of environmental problems and teach them how to protect nature and use resources responsibly.

2. How is particulate matter released in the atmosphere?
Particulate matter is released through vehicle emissions, industrial activities, burning of fossil fuels, and construction activities.

3. Which gas is more poisonous, CO₂ or CO?
Carbon monoxide (CO) is more poisonous because it binds to hemoglobin in blood, reducing oxygen supply to the body.

4. How does acid rain affect forests?
Acid rain damages tree leaves, weakens roots, and makes soil acidic, harming plant growth.

5. In what way is sulfur present in fossil fuels dangerous?
When fossil fuels are burned, sulfur is released as sulfur dioxide (SO₂), which can cause acid rain and respiratory problems.

6. Name any three major sources responsible for the greenhouse effect.
The major sources are:

  • Burning of fossil fuels (CO₂)
  • Agriculture (CH₄ from livestock)
  • Deforestation (less CO₂ absorption).

7. How is geothermal energy useful for us?
Geothermal energy is used to generate electricity and provide heating by using heat from inside the Earth.

Constructed Response Questions

i. How is the excessive use of insecticides and pesticides harmful for birds?
Insecticides and pesticides contain harmful chemicals that can enter the food chain. When birds eat insects or seeds contaminated with these chemicals, they can get poisoned. Pesticides can weaken birds’ immune systems, affect their reproduction by thinning eggshells, and even lead to their death. Overuse of such chemicals also reduces the availability of insects that birds feed on, disrupting their natural diet.

ii. Percentage of CO₂ in air is only 0.03%. Then how does it become harmful for the ecosystem?
Even though CO₂ is present in small amounts, it plays a significant role in trapping heat in the Earth’s atmosphere. Excess CO₂ from activities like burning fossil fuels causes global warming, leading to climate change. This disrupts weather patterns, melts glaciers, raises sea levels, and affects ecosystems, harming plants, animals, and humans. It also makes oceans acidic, threatening marine life.

iii. Why only some pollutant gases present in the atmosphere cause greenhouse effect while others do not?
Gases like CO₂, CH₄ (methane), and N₂O absorb heat and trap it in the atmosphere, causing the greenhouse effect. These gases are called greenhouse gases because they allow sunlight to enter the Earth but prevent heat from escaping. Other gases, like nitrogen (N₂) and oxygen (O₂), do not have this property, so they don’t contribute to the greenhouse effect.

iv. How can you reduce the emission of CO present in the gases emitted by the burning of fuel in automobile engines?
To reduce CO emissions:

  1. Use catalytic converters in vehicles to convert CO into less harmful gases.
  2. Use cleaner fuels like compressed natural gas (CNG) or electric vehicles.
  3. Maintain vehicles regularly to ensure efficient fuel burning.
  4. Carpooling and public transport reduce the number of vehicles on the road, lowering emissions.

v. Mention three different ways in which solar energy can be useful for us.

  1. Electricity Generation: Solar panels convert sunlight into electricity for homes, schools, and industries.
  2. Heating: Solar energy can be used to heat water and buildings, reducing the use of gas or electricity.
  3. Cooking: Solar cookers use sunlight to prepare food without using gas or electricity, making them eco-friendly.

Descriptive Questions

i. Describe the harmful effects of the major pollutants present in the air.

  • Carbon monoxide (CO): Reduces oxygen supply to the body, causing dizziness, fatigue, and even death.
  • Sulfur dioxide (SO₂): Causes acid rain, damages plants, and irritates the respiratory system.
  • Nitrogen oxides (NOₓ): Contribute to smog and acid rain and affect lung function.
  • Particulate matter (PM): Tiny particles can enter the lungs, causing breathing issues, asthma, and heart problems.
  • Ozone (O₃): At ground level, it causes respiratory problems and harms crops and materials.

ii. Explain greenhouse effect. How is global warming dangerous for us?
The greenhouse effect is the process by which certain gases (like CO₂, CH₄, and N₂O) trap heat in the Earth’s atmosphere, keeping the planet warm. This is essential for life, but excessive greenhouse gases lead to global warming.
Global warming is dangerous because it:

  • Causes extreme weather events like hurricanes and floods.
  • Melts glaciers, raising sea levels and flooding coastal areas.
  • Disrupts ecosystems, endangering animals and plants.
  • Makes some regions too hot or dry for farming, leading to food shortages.

iii. What is air quality index? What information does it convey?
The Air Quality Index (AQI) measures the quality of air in a specific area and tells us how clean or polluted the air is. It assigns a score or color based on pollutants like CO, NO₂, PM, and O₃.

  • Good AQI: Air is clean and safe to breathe.
  • Poor AQI: Air is polluted and can harm health, especially for sensitive groups like children and the elderly.

iv. Who are at high risk groups and why is pollution more dangerous for them?
High-risk groups include:

  • Children: Their lungs are still developing, and they breathe faster than adults, so they inhale more polluted air.
  • Elderly people: They often have weaker immune systems and pre-existing health problems like asthma or heart disease.
  • Pregnant women: Pollution can harm the developing baby.
  • People with respiratory issues: They are more sensitive to pollutants, which can worsen their conditions.

v. Describe three strategies to address environmental issues.

  1. Reduce Pollution: Use renewable energy sources (solar, wind) and improve waste management to reduce air, water, and land pollution.
  2. Conservation of Resources: Save water, use energy-efficient appliances, and plant more trees to conserve natural resources.
  3. Raise Awareness: Educate people about the importance of protecting the environment through schools, campaigns, and community programs.

Investigative Questions

i. Major Pakistani cities experience a very high AQI in winter. Point out some of the major causes of high AQI in these cities.

  • Vehicle Emissions: Increased use of vehicles releases pollutants like CO, NOₓ, and particulate matter.
  • Industrial Emissions: Factories release smoke containing SO₂ and other harmful gases.
  • Burning of Crop Residue: Farmers burn crop stubble, which adds to air pollution.
  • Temperature Inversion: In winter, cooler air traps pollutants near the ground, worsening air quality.

ii. Why does AQI not rise in Pakistan in hot days of summer?
In summer, higher temperatures and winds disperse pollutants, preventing them from accumulating near the ground. Unlike winter, there is no temperature inversion to trap pollutants.

iii. How has climate change affected Pakistan during the last five years?

  • Increased Floods: Heavy rains and melting glaciers have caused severe flooding, displacing millions of people.
  • Heatwaves: High temperatures have caused heat-related illnesses and deaths.
  • Droughts: Some regions face water shortages due to irregular rainfall.
  • Crop Damage: Changing weather patterns have affected agricultural production, leading to food insecurity.

Group Properties and Elements: SLO-Based Guide for 9th Class (2025 Punjab Boards)

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Master group properties and elements with this SLO-based guide for 9th class. Perfect for Lahore Board and Punjab Boards, aligned with the 2025 syllabus and solved exercises.

Multiple choice Questions

1. Which halogen will have the least reactivity with alkaline earth metals?

  • (a) Chlorine
  • (b) Bromine
  • (c) Iodine
  • (d) Fluorine

Correct Answer: (c) Iodine
Explanation: Reactivity decreases as we move down the halogen group because the atomic size increases, making it harder to gain electrons. Iodine is the least reactive among the given options.
Tip: Remember that reactivity of halogens decreases down the group in the periodic table.

2. Which compound do you expect to be colored?

  • (a) KCl
  • (b) BaCl₂
  • (c) AlCl₃
  • (d) NiCl₂

Correct Answer: (d) NiCl₂
Explanation: Transition metal compounds like NiCl₂ are often colored due to the d-electrons absorbing specific wavelengths of light.
Tip: If the compound contains a transition metal, it is likely to be colored.

3. In which element exists the strongest forces of attraction between atoms?

  • (a) Mg
  • (b) Ca
  • (c) Sr
  • (d) Ba

Correct Answer: (a) Mg
Explanation: Magnesium atoms have a smaller atomic radius and higher charge density compared to the other options, leading to stronger metallic bonding.
Tip: Smaller atomic size and higher charge density usually mean stronger forces of attraction.

4. Elements of which group are all colored?

  • (a) Second group
  • (b) Sixth group
  • (c) Fourth group
  • (d) Fifth group

Correct Answer: (b) Sixth group
Explanation: Group 6 elements, particularly transition metals like chromium and molybdenum, form colored compounds.
Tip: Look for transition elements for color trends in compounds.

5. Which halogen acid is unstable at room temperature?

  • (a) HBr
  • (b) HI
  • (c) HCl
  • (d) HF

Correct Answer: (b) HI
Explanation: Hydrogen iodide (HI) is unstable because it easily decomposes into hydrogen gas and iodine due to weak bonding between H and I atoms.
Tip: The strength of halogen acids decreases as the size of the halogen atom increases.

6. Which oxide is the most basic?

  • (a) Na₂O
  • (b) Li₂O
  • (c) MgO
  • (d) CO

Correct Answer: (a) Na₂O
Explanation: Sodium oxide is a strong basic oxide as it reacts readily with water to form NaOH, a strong base.
Tip: Metal oxides from Group 1 elements are typically the most basic.

7. Which group elements are the most reactive elements?

  • (a) Transition metals
  • (b) First group
  • (c) Second group
  • (d) Third group

Correct Answer: (b) First group
Explanation: Group 1 elements (alkali metals) are the most reactive because they have a single electron in their outermost shell, which they lose easily.
Tip: Reactivity increases as you go down Group 1.

8. The following solutions of a halogen and a sodium halide are mixed. Which solution will turn dark because of a reaction?

  • (a) Br₂ and NaCl
  • (b) Br₂ and NaF
  • (c) Cl₂ and NaI
  • (d) Cl₂ and NaCl

Correct Answer: (c) Cl₂ and NaI
Explanation: Chlorine is more reactive than iodine, so it displaces iodine from sodium iodide, forming dark iodine (I₂).
Tip: A more reactive halogen can displace a less reactive halogen from its compound.

9. X is a monoatomic gas. Which statement about this is correct?

  • (a) X burns in air
  • (b) X is colored
  • (c) X is unreactive
  • (d) X will displace iodine from it

Correct Answer: (c) X is unreactive
Explanation: Monoatomic gases like noble gases are chemically inert due to their stable electronic configuration.
Tip: Noble gases are always monoatomic and unreactive.

10. Which property is correct for Group 1 elements?

  • (a) Low electrical conductivity
  • (b) High density
  • (c) Low melting point
  • (d) High melting point

Correct Answer: (c) Low melting point
Explanation: Group 1 metals have relatively low melting points compared to other metals due to their large atomic sizes and weak metallic bonds.
Tip: Group 1 elements exhibit low density, low melting points, and high reactivity.

Short Questions

i. Why does it become easier to cut an alkali metal when we move from top to bottom in Group I?

  • Alkali metals become softer as we go down the group because their atoms get larger and the metallic bonds become weaker.

ii. Predict the reactivity of potassium towards halogens.

  • Potassium reacts very vigorously with halogens like chlorine to form potassium halides (e.g., KCl), releasing energy and producing a salt.

iii. In the following reaction, chlorine acts as a reducing agent. What is the oxidizing agent?

  • The oxidizing agent is NaBr because bromine (Br) is gaining electrons.

iv. Why does iodine exist in the solid state at room temperature?

  • Iodine exists as a solid because its molecules are large and have strong intermolecular forces (van der Waals forces) that hold them together in a solid structure.

v. How does Ni catalyze the reaction involving hydrogenation of oil?

  • Nickel (Ni) acts as a catalyst by providing a surface where hydrogen and oil molecules can interact more effectively, speeding up the reaction to convert unsaturated fats into saturated fats.

3. Constructed Response Questions

i. Which noble gas should have the lowest boiling point and why?

  • Helium has the lowest boiling point because it is the smallest noble gas atom, resulting in the weakest intermolecular forces (London dispersion forces). This makes it easier to convert helium into a gas.

ii. Compare the reactions of alkali metals with chlorine.

  • Alkali metals react vigorously with chlorine to form metal chlorides. For example, sodium reacts with chlorine to form sodium chloride (NaCl). The reaction produces heat and light:
    2Na+Cl2→2NaCl

iii. Why are almost all the metals solids while non-metals generally exist as gases and solids?

  • Metals have strong metallic bonds due to free-moving electrons, which make them solid at room temperature. Non-metals have weak intermolecular forces, which is why many exist as gases or brittle solids.

iv. Name any three elements in the periodic table which exist as liquids.

  • Mercury (Hg), Bromine (Br), and Gallium (Ga).

v. Why are transition elements different from normal elements?

  • Transition elements have partially filled d-orbitals, which give them unique properties such as variable oxidation states, formation of colored compounds, and catalytic behavior.

vi. Compare the reactivity of chlorine and bromine as reducing agents.

  • Chlorine is a stronger oxidizing agent than bromine because it has a higher electronegativity and a smaller atomic size, allowing it to gain electrons more easily.

vii. Which element is the most reactive and which is the least reactive among halogens? Give two reasons to explain your answer.

  • Most reactive: Fluorine, because it has the highest electronegativity and smallest atomic size.
    Least reactive: Iodine, because it has the lowest electronegativity and largest atomic size among halogens.

4. Descriptive Questions

i. Explain the role of a catalytic converter in an automobile.

  • A catalytic converter reduces harmful emissions from vehicle exhaust. It converts toxic gases like carbon monoxide (CO) and nitrogen oxides (NOx) into less harmful gases like carbon dioxide (CO₂) and nitrogen (N₂). Platinum and palladium in the converter act as catalysts.

ii. Why do the chemical reactivities of alkali metals increase down the group, whereas they decrease down the group in case of halogens?

  • Alkali metals: Reactivity increases down the group because their atomic size increases, and the outer electron is farther from the nucleus, making it easier to lose.
  • Halogens: Reactivity decreases down the group because their atomic size increases, reducing the ability to gain electrons due to weaker nuclear attraction.

iii. Why are metals generally tough and strong, whereas non-metals are neither tough nor strong?

  • Metals: They have strong metallic bonds formed by a “sea” of free electrons that hold the metal ions together, making them tough and strong.
  • Non-metals: They have weak covalent bonds or intermolecular forces, making them brittle or soft.

iv. Both alkali metals and halogens are very reactive elements with roles opposite to each other. Explain.

  • Alkali metals lose electrons to form positive ions (cations), making them strong reducing agents. Halogens gain electrons to form negative ions (anions), making them strong oxidizing agents. Their reactivity arises due to their tendency to achieve stable electronic configurations.

v. Why is hydrogen bromide thermally unstable compared to hydrogen chloride?

  • Hydrogen bromide has a weaker bond compared to hydrogen chloride because bromine is larger than chlorine, resulting in a longer and weaker bond. This makes HBr decompose at lower temperatures.

vi. Compare the properties of metals and non-metals.

  • Metals: Good conductors of heat and electricity, malleable, ductile, and have high melting points.
  • Non-metals: Poor conductors of heat and electricity, brittle, not ductile, and generally have lower melting points.

vii. Why is V₂O₅ catalyst preferred over platinum in the oxidation of sulfur dioxide? Give reasons.

  • V₂O₅ is less expensive, more efficient at high temperatures, and remains stable during the oxidation process, whereas platinum is costly and can be poisoned by impurities.

5. Investigative Questions

i. Explain the role of sodium as a heat transfer agent in the atomic nuclear power plant. Which property of sodium is utilized in this role?

  • Sodium is used because it has a high thermal conductivity and a wide liquid temperature range. It efficiently transfers heat from the reactor to the steam generator without boiling at high temperatures.

ii. Why and how does lithium behave differently from the rest of the alkali metals?

  • Lithium has a smaller atomic size, higher ionization energy, and stronger covalent character. It reacts less vigorously with water and forms a stable oxide (Li₂O) instead of a peroxide or superoxide.

iii. Why aluminum metal is used in the manufacture of cooking utensils, whereas magnesium is not considered useful for this purpose?

  • Aluminum is lightweight, has good thermal conductivity, and resists corrosion due to the formation of an oxide layer. Magnesium, though lightweight, is not preferred because it is less durable and reacts more readily with food and water.

Periodic Table and Periodicity, Solved Exercise for 9th Class (2025 Punjab Boards)

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Explore the periodic table and periodicity with this SLO-based solved exercise for 9th class students. Aligned with the new 2025 syllabus, ideal for Lahore Board and all Punjab Boards.

Multiple choice questions

1. In which period and group will you place the element which is an important part of the solar cell?
Options:
(a) Third period and fourth group
(b) Second period and fourth group
(c) Third period and sixth group
(d) Third period and fifth group
Correct Answer: (c) Third period and sixth group
Explanation: The element used in solar cells is silicon, which is in the third period and sixth group of the periodic table.

2. Identify the electronic configuration of the outermost shell of a transition metal.
Options:
(a) ns²np⁴
(b) nd⁵ns²
(c) ns⁴np²
(d) ns³np³
Correct Answer: (b) nd⁵ns²
Explanation: Transition metals typically have electrons in the (n-1)d and ns orbitals, such as nd⁵ns² for a partially filled d-subshell.

3. Which is the softest metal?
Options:
(a) Na
(b) Ca
(c) Al
(d) Zn
Correct Answer: (a) Na
Explanation: Sodium (Na) is an alkali metal, and its softness is due to its relatively large atomic size and weak metallic bonds.

4. A yellow solid element exists in allotropic forms, which is also present in fossil fuel. Name the element.
Options:
(a) Carbon
(b) Iodine
(c) Aluminium
(d) Sulphur
Correct Answer: (d) Sulphur
Explanation: Sulphur is a yellow solid, has various allotropes, and is found in fossil fuels like coal.

5. How many electrons can nitrogen accept in its outermost shell?
Options:
(a) 2
(b) 3
(c) 4
(d) 5
Correct Answer: (b) 3
Explanation: Nitrogen has 5 electrons in its outer shell and needs 3 more to complete its octet.

6. Which element is the most reactive element?
Options:
(a) Oxygen
(b) Chlorine
(c) Fluorine
(d) Nitrogen
Correct Answer: (c) Fluorine
Explanation: Fluorine is the most reactive due to its high electronegativity and small atomic size.

7. Which element has the highest melting point?
Options:
(a) Na
(b) Ca
(c) Rb
(d) Cs
Correct Answer: (b) Ca
Explanation: Calcium has stronger metallic bonds compared to other alkali or alkaline earth metals listed.

8. In what order does the metallic character change in the second group?
Options:
(a) Mg > Ca > Ba > Sr
(b) Sr > Ba > Ca > Mg
(c) Mg > Sr > Ba > Ca
(d) Ba > Sr > Mg > Ca
Correct Answer: (d) Ba > Sr > Mg > Ca
Explanation: Metallic character increases down the group in the periodic table.

9. Which of the following best describes the correct order of oxygen, fluorine, and nitrogen’s atomic radii?
Options:
(a) O < F < N
(b) N < F < O
(c) F < O < N
(d) O < N < F
Correct Answer: (c) F < O < N
Explanation: Atomic radius decreases across a period. Nitrogen > Oxygen > Fluorine.

10. Which of the following elements has d-electrons filled completely?
Options:
(a) Zn
(b) Ca
(c) Al
(d) Fe
Correct Answer: (a) Zn
Explanation: Zinc has a completely filled d-subshell (3d¹⁰).

Q2 Short Questions

i. Why was atomic number chosen to arrange the elements in the periodic table?
Answer: Atomic number represents the number of protons in an atom, which determines its identity and chemical properties. Arranging elements by atomic number ensures that elements with similar properties are grouped together systematically.

ii. What is the significance of the word “periodic”?
Answer: The word “periodic” signifies the repeating pattern of chemical properties of elements when they are arranged in order of increasing atomic number.

iii. Why does the size of a period increase as we move down the periodic table?
Answer: As we move down the periodic table, new electron shells are added, increasing the distance between the outermost electrons and the nucleus, which results in a larger atomic size.

iv. In a group, the elements have the same number of electrons in the outermost shell. Why is it so?
Answer: Elements in the same group have the same number of valence electrons because they share the same electron configuration in their outermost shell. This gives them similar chemical properties.

v. Do you expect calcium to be more reactive than sodium? Give the reason for your answer.
Answer: No, sodium is more reactive than calcium. Sodium is an alkali metal in Group 1, and it loses its single valence electron more easily than calcium, which belongs to Group 2 and has two valence electrons to lose.

vi. Which element has the maximum atomic radius and which element has the minimum atomic radius in the third period?
Answer: In the third period, sodium (Na) has the maximum atomic radius, and chlorine (Cl) has the minimum atomic radius because atomic size decreases across a period due to increasing nuclear charge.

vii. Why are the most electronegative elements present in the sixth and seventh groups?
Answer: Groups 6 and 7 contain nonmetals like oxygen, sulfur, fluorine, and chlorine, which have a strong tendency to attract electrons to complete their octet. This high attraction makes them highly electronegative.

viii. The first ionization energy value of magnesium is less than the second one. Give reason.
Answer: The first ionization energy removes one valence electron, which is loosely held. The second ionization energy requires removing an electron from a stable, fully filled orbital, requiring significantly more energy.

ix. Is it possible for two metals or two non-metals to form an ionic bond?
Answer: No, ionic bonds are typically formed between a metal and a non-metal due to the transfer of electrons. Two metals or two non-metals cannot easily transfer electrons in this way.

x. Which element has the least value of ionization energy and which element has the highest value of electronegativity?
Answer:

  • Least ionization energy: Cesium (Cs), as it is a large alkali metal with loosely held valence electrons.
  • Highest electronegativity: Fluorine (F), due to its small size and high nuclear charge, which strongly attracts electrons.

Constructed Response Questions

i. Suppose a new element is discovered. Where would you like to accommodate this element in the periodic table?
Answer: To place a new element in the periodic table, we must first determine its atomic number and electronic configuration. These will help identify the group and period it belongs to. For example:

  • Group: The number of valence electrons will indicate the group.
  • Period: The number of electron shells will determine the period.
    By knowing these properties, the new element can be placed in the correct position in the periodic table to match its chemical and physical properties with similar elements.

ii. What is the first element of the periodic table? Will it lose or gain an electron?
Answer: The first element of the periodic table is hydrogen. It has one electron in its outer shell and can lose this electron to form H⁺ (like metals) or gain one electron to form H⁻ (like non-metals), depending on the chemical environment.

iii. Atomic radii of boron and aluminum are 88 pm and 125 pm, respectively. Which element is expected to lose electrons more easily?
Answer: Aluminum is expected to lose electrons more easily because it has a larger atomic radius (125 pm). The larger the atomic radius, the weaker the attraction between the nucleus and the outer electrons, making it easier to lose electrons.

iv. How would you find the atomic radius of an atom?
Answer: The atomic radius is measured as half the distance between the nuclei of two identical atoms that are bonded together. Scientists use techniques like X-ray diffraction or spectroscopy to measure this distance accurately.

v. Why is it not possible for an oxygen atom to accept three electrons to form O³⁻, unlike nitrogen which can accept electrons to form N³⁻?
Answer: Oxygen has 6 valence electrons, so accepting three electrons would result in 9 electrons in the outer shell, exceeding the stable octet rule. This would create too much electron-electron repulsion, making O³⁻ unstable. Nitrogen, with 5 valence electrons, can accept 3 electrons to form a stable N³⁻ ion.

Descriptive Questions

i. Which information is needed to locate elements in the periodic table if you do not know its atomic number? Is atomic mass helpful for this purpose?
Answer:
To locate an element:

  • Atomic Number: This is the most accurate way to locate an element, as it directly determines its position.
  • Atomic Mass: It can provide a clue, but it is not always reliable because elements with similar masses may belong to different groups (e.g., isotopes).
    In summary, atomic number is more helpful than atomic mass for identifying an element’s position.

ii. How many blocks of elements are present in the periodic table? Are these blocks helpful in studying the properties of elements?
Answer:
There are four blocks in the periodic table: s-block, p-block, d-block, and f-block. These blocks are very helpful because they group elements based on their valence electron configuration, which determines chemical properties. For example:

  • s-block elements are highly reactive metals.
  • p-block contains both metals and non-metals.
  • d-block elements are transition metals with variable oxidation states.
  • f-block elements include lanthanides and actinides.

iii. Explain the variation in the following properties in the periods giving reasons:
(a) Atomic Radius:

  • Atomic radius decreases across a period because of increasing nuclear charge, which pulls the electrons closer to the nucleus.
    (b) Ionization Energy:
  • Ionization energy increases across a period because the electrons are held more tightly due to increasing nuclear charge, requiring more energy to remove them.

iv. Which physical properties of elements may lead us to know what type of bond it will form?
Answer:
Physical properties like ionization energy, electronegativity, and atomic radius help predict bond type:

  • Elements with low ionization energy and large atomic radius form ionic bonds.
  • Elements with high electronegativity form covalent bonds.

v. Write down the names of four non-metals which exist in solid state at normal temperature.
Answer:

  • Carbon
  • Sulfur
  • Phosphorus
  • Iodine

vi. Why do second and third periods have equal numbers of elements while all other periods contain different numbers?
Answer:
The second and third periods have 8 elements each because their outermost electron shell can hold a maximum of 8 electrons. In contrast, higher periods (4th and beyond) involve d and f orbitals, which allow for more elements.

Investigative Questions

i. Why is the periodic table considered a remarkable achievement?
Answer:
The periodic table organizes elements systematically based on their properties and atomic number. Its benefits include:

  • Predicting chemical behavior of elements.
  • Identifying trends in properties like atomic radius, electronegativity, etc.
  • Helping discover new elements by identifying gaps in the table.

ii. Why do lithium and beryllium behave differently from other alkali and alkaline earth metals?
Answer:
Lithium and beryllium have smaller atomic sizes and higher ionization energies compared to other elements in their groups. For example:

  • Lithium forms a strong bond with water, unlike sodium.
  • Beryllium shows covalent bonding, unlike other alkaline earth metals that form ionic bonds.

iii. How is the modern periodic table different from Mendeleev’s periodic table?
Answer:

  • Mendeleev’s Table: Organized by atomic mass, had gaps for undiscovered elements, and grouped some elements with different properties.
  • Modern Table: Organized by atomic number, includes all discovered elements, and uses a clear block structure (s, p, d, f).

New Syllabus Chemistry Chapter 7: Acid-Base Chemistry – Lahore Board Guide

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Explore Chapter 7 of the new Lahore Board Chemistry syllabus, dedicated to Acid-Base Chemistry. This comprehensive guide simplifies key concepts such as the Arrhenius, Bronsted–Lowry, and Lewis theories of acids and bases, pH scale, neutralization reactions, titration techniques, and industrial applications. Ideal for students preparing for exams, this resource includes easy explanations, solved examples, MCQs, short questions, and detailed practice problems aligned with the latest syllabus. Boost your understanding of acid-base reactions and excel in your exams with this in-depth content!

Question (i):

Which acid is not used as a food or mixed with food?
Options:
(a) Tartaric acid
(b) Ascorbic acid
(c) Citric acid
(d) Formic acid
Correct Answer: (d) Formic acid
Explanation: Tartaric acid, ascorbic acid, and citric acid are commonly used in food products as preservatives or flavoring agents, whereas formic acid is not used in food due to its toxic and corrosive properties.

Question (ii):

While baking, which gas is responsible for raising the bread and making it soft?
Options:
(a) Oxygen
(b) Carbon dioxide
(c) Nitrogen
(d) Carbon monoxide
Correct Answer: (b) Carbon dioxide
Explanation: Baking powder or yeast releases carbon dioxide gas during baking, which causes the dough to rise and become soft.

Question (iii):

Predict the main characteristics of the reactions of metals with acids.
Options:
(a) Metals are dissolved
(b) Metals are converted into salts
(c) Hydrogen gas is evolved
(d) All the above-mentioned characteristics are true
Correct Answer: (d) All the above-mentioned characteristics are true
Explanation: When metals react with acids, they dissolve to form metal salts, and hydrogen gas is released as a by-product.

Question (iv):

How many hydroxide ions will calcium hydroxide release in water?
Options:
(a) 1
(b) 2
(c) Zero
(d) 3
Correct Answer: (b) 2
Explanation: Calcium hydroxide (Ca(OH)2) dissociates in water to release two hydroxide ions (OH⁻) per formula unit.

Question (v):

In a neutralization reaction between KOH and H3PO4, how many molecules of KOH will react with one molecule of H3PO4?
Options:
(a) 2
(b) 1
(c) 3
(d) 4
Correct Answer: (c) 3
Explanation: H3PO4 is a triprotic acid and can donate three hydrogen ions, requiring three KOH molecules to fully neutralize it.

Question (vi):

Which acid is used in the preparation of soap?
Options:
(a) Tartaric acid
(b) Citric acid
(c) Stearic acid
(d) Oxalic acid
Correct Answer: (c) Stearic acid
Explanation: Stearic acid is used in soap manufacturing because it reacts with a base (e.g., NaOH) to form soap through saponification.

Question (vii):

Which compound is formed when SO2 is dissolved in water?
Options:
(a) SO3
(b) H2SO3
(c) H2SO4
(d) H2S2O7
Correct Answer: (b) H2SO3
Explanation: When SO2 (sulfur dioxide) dissolves in water, it forms sulfurous acid (H2SO3).

Question (viii):

Which of the following contains oxalic acid?
Options:
(a) Tomato
(b) Orange
(c) Tamarind
(d) Sour milk
Correct Answer: (a) Tomato
Explanation: Tomatoes contain oxalic acid naturally, which contributes to their slightly acidic taste.

Question (ix):

Which compound in the following reaction is behaving as a conjugate base?
CH3COOH+H2O⇋CH3COO−+H3O+
Options:
(a) CH3COOH
(b) H2O
(c) CH3COO−
(d) H3O+
Correct Answer: (c) CH3COO−
Explanation: In the reaction, CH3COOH donates a proton to water, forming CH3COO−, which is its conjugate base.

Question (x):

When a chemical reaction is carried out with a substance Z, a gas is produced which turns red litmus paper blue. What is the reaction?
Options:
(a) Reaction of an acid with a metal carbonate
(b) Reaction of an acid with a base
(c) Reaction of an acid with a metal oxide
(d) Reaction of an acid with ammonium salt
Correct Answer: (b) Reaction of an acid with a base
Explanation: The reaction between an acid and a base produces ammonia gas (NH3 or similar compounds, which turn red litmus blue due to their basic nature.

2. Questions for Short Answers

(i) Choose Arrhenius Acids among the following compounds:

HF, NH3, H2SO4, SO2, H2S, H2O
Answer: HF, H2SO4, H2S, and H2O.
Explanation: According to the Arrhenius concept, acids are substances that increase H+concentration in water. HF, H2SO4, and H2S release H+ ions when dissolved in water, making them Arrhenius acids. Water (H2O) can also act as a weak acid in certain reactions.

(ii) How does calcium metal react with dilute H2SO4?

Answer: Calcium reacts with dilute sulfuric acid to produce hydrogen gas and calcium sulfate:
Ca+H2SO4→CaSO4+H2
Explanation: Calcium is a reactive metal that displaces hydrogen from sulfuric acid, forming an ionic salt (CaSO4) and hydrogen gas.

(iii) Which salt is formed when HCl reacts with BaCO3?

Answer: Barium chloride (BaCl2) is formed.
Reaction:
BaCO3+2HCl→BaCl2+CO2+H2O
Explanation: Hydrochloric acid reacts with barium carbonate to form barium chloride, releasing carbon dioxide gas and water as by-products.

(iv) How will you justify that HSO4−is a Bronsted–Lowry acid?

Answer: HSO4−can donate a proton (H+) to form SO42−:
HSO4−⇋SO42−+H+
Explanation: According to the Bronsted–Lowry concept, acids are proton donors. HSO4– donates a proton in this reaction, making it a Bronsted–Lowry acid.

(v) What chemical name will you give to soap as a compound?

Answer: Soap is chemically called sodium stearate or potassium stearate, depending on the alkali used.
Explanation: Soaps are salts of fatty acids (like stearic acid) formed by the reaction of a base (e.g., NaOH) with a fat or oil in the process of saponification. For example:
C17H35COOH+NaOH→C17H35COONa+H2O
This reaction forms sodium stearate, which is the chemical name for soap.

4. Descriptive Questions

(i) Explain Arrhenius concept of acids and bases.

The Arrhenius concept defines acids and bases based on their behavior in water:

  • Acids: Substances that increase the concentration of hydrogen ions (H+) or protons in an aqueous solution. For example, HCl dissociates in water to produce H+ ions:
    HCl→H++Cl−
  • Bases: Substances that increase the concentration of hydroxide ions (OH−) in an aqueous solution. For example, NaOH dissociates in water to produce OH−:
    NaOH→Na++OH−

The Arrhenius concept is simple but limited to aqueous solutions. It does not explain the behavior of substances like NH3, which acts as a base but does not contain OH− ions.

(ii) Compare Arrhenius and Bronsted–Lowry concepts of acids and bases.

  • Arrhenius Concept:
    • Acids are substances that increase H+ ion concentration in water.
    • Bases are substances that increase OH− ion concentration in water.
    • Limited to aqueous solutions.
    • Example: HCl is an acid, and NaOH is a base.
  • Bronsted–Lowry Concept:
    • Acids are proton (H+) donors.
    • Bases are proton (H+) acceptors.
    • Not restricted to aqueous solutions.
    • Example: NH3 accepts a proton to form NH4+, acting as a base.

The Bronsted–Lowry concept is more general and can describe acid-base behavior in non-aqueous systems.

(iii) How does sulphuric acid react with the following compounds?

  1. NH4Cl:
    H2SO4 reacts with NH4Cl to release hydrogen chloride gas:
    NH4Cl+H2SO4→NH4HSO4+HCl
    This is an acid-base reaction where H2SO4 acts as a stronger acid.
  2. NH3:
    H2SO4 reacts with NH3 to form ammonium sulfate:
    2NH3+H2SO4→(NH4)2SO4
    The reaction neutralizes H2SO4, producing a salt.
  3. MgO:
    H2SO4 reacts with MgO to form magnesium sulfate and water:
    MgO+H2SO4→MgSO4+H2O
    This reaction shows that magnesium oxide acts as a basic oxide.
  4. MgCO3:
    H2SO4 reacts with MgCO3 to produce magnesium sulfate, carbon dioxide, and water:
    MgCO3+H2SO4→MgSO4+CO2+H2O
    This is a typical reaction of acids with carbonates.

(iv) What happens when a base reacts with a non-metallic oxide? What do you infer about the nature of non-metallic oxide?

When a base reacts with a non-metallic oxide, a salt and water are formed. For example:
2NaOH+CO2→Na2CO3+H2O
This reaction indicates that non-metallic oxides are acidic in nature, as they react with bases to form salts and water.

(v) State the reason for showing acidic character by both dry HCl gas and HCl solution in water.

  • Dry HCl Gas: Dry HCl does not ionize because there is no water to dissociate it into H+ and Cl−. It does not show acidic properties in the absence of water.
  • HCl in Water: In water, HCl ionizes completely to form H+ ions, which are responsible for its acidic character:
    HCl→H++Cl−

Thus, the presence of water is essential for HCl to exhibit acidic properties.

(vi) Differentiate between an acid and its conjugate base.

  • Acid: A substance that donates a proton (H+) in a chemical reaction.
  • Conjugate Base: The species that remains after the acid has donated its proton.

Example:
In the reaction:
CH3COOH⇋CH3COO−+H+

  • CH3COOH is the acid.
  • CH3COO− is its conjugate base.

Acids and their conjugate bases differ by one proton.

5. Investigative Questions

(i) Why is significant CO2 passing through limewater on this statement?

When CO2 gas is passed through limewater (Ca(OH)2, it initially reacts to form insoluble calcium carbonate (CaCO3), which turns the solution milky:
CO2+Ca(OH)2→CaCO3+H2O
If more CO2CO_2 is passed, the calcium carbonate reacts further to form soluble calcium bicarbonate, causing the milkiness to disappear:
CaCO3+CO2+H2O→Ca(HCO3)2
This demonstrates that the reaction depends on the concentration of CO2 and the solubility of the products.

(ii) What is observed when CO2 is passed through limewater for a short duration (a) and for a long duration (b)?

  • (a) Short Duration: Limewater turns milky due to the formation of insoluble calcium carbonate:
    CO2+Ca(OH)2→CaCO3+H2O
  • (b) Long Duration: The milkiness disappears because calcium carbonate reacts with excess CO2 and water to form soluble calcium bicarbonate:
    CaCO3+CO2+H2O→Ca(HCO3)2

This reaction is used as a test for the presence of CO2 gas.

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