chemistry MCQs Archives

Ethics and Values in Chemistry: Unit 1 Solved Exercises | 2nd Year Federal Board New Book

June 12, 2025 by samreen

Short Answer Questions:

i. Define cognitive bias.

Answer: Cognitive bias is a systematic error in thinking that influences judgments and decisions based on personal experiences, emotions, or subconscious preferences rather than objective evidence.
Key Concept: Subjective thinking patterns leading to irrational conclusions.
Tip/Trick: Remember: Bias = Brain’s shortcuts. Examples: Confirmation bias (favoring info that agrees with beliefs), availability bias (overweighting recent examples).

ii. What is a false cause fallacy?

Answer: False cause fallacy (or post hoc ergo propter hoc) assumes Event A caused Event B solely because A occurred before B, ignoring other factors.
Example: “I wore a lucky shirt, then passed my exam; the shirt caused my success.”
Key Concept: Confusing correlation with causation.
Tip/Trick: Ask: “Is there actual evidence linking cause and effect, or just timing?”

iii. Describe the straw man fallacy.

Answer: The straw man fallacy misrepresents an opponent’s argument as a weaker, distorted version to make it easier to attack.
Example: Original: “Reduce plastic use.” Straw man: “You want to ban all plastics and collapse industries!”
Key Concept: Intellectual dishonesty through distortion.
Tip/Trick: Spot phrases like “So you’re saying…” followed by an exaggerated claim.

iv. What does the fallacy of exclusion involve?

Answer: Fallacy of exclusion ignores crucial evidence that contradicts a claim, presenting an incomplete or biased view.
Example: “Chemical X is safe” (while hiding studies showing toxicity).
Key Concept: Cherry-picking data to support a narrative.
Tip/Trick: Always ask: “What evidence is missing?”

v. Give an example of a faulty analogy.

Answer: “Regulating chemicals is like banning cars because accidents happen – both stifle progress.”
Why faulty: Cars and chemical regulations aren’t comparable in risk scope or societal impact.
Key Concept: Weak comparisons that ignore critical differences.
Tip/Trick: Check if the analogy shares essential similarities. If not, it’s faulty.

vi. List one pro and one con of chemical substances.

Answer:

Pro: Pharmaceuticals save lives (e.g., antibiotics treat infections).
Con: Pesticides can contaminate ecosystems (e.g., DDT harming birds).
Key Concept: Dual nature of chemicals: lifesaving vs. harmful.
Tip/Trick: Pros relate to human progress; cons to unintended consequences.

vii. Responsibility of scientists/companies in chemical production.

Answer: Ensure safety through rigorous testing, transparent risk disclosure, ethical waste management, and compliance with regulations.
Example: Testing industrial solvents for long-term environmental impact.
Key Concept: Ethical duty to prioritize people and planet over profit.
Tip/Trick: Remember the precautionary principle: “Better safe than sorry.”

viii. Importance of regulations in the chemical industry.

Answer: Regulations enforce safety standards, prevent pollution, hold companies accountable, and protect public/environmental health.
Example: REACH laws in the EU ban carcinogenic chemicals.
Key Concept: Legal frameworks as safeguards against negligence.
Tip/Trick: Link to historical failures (e.g., Bhopal disaster → stricter laws).

ix. What is a claim in a scientific argument?

Answer: A claim is a statement asserting a fact or position, supported by evidence and reasoning.
Example: “Lead pollution reduces children’s IQ scores.”
Key Concept: Foundation of an argument requiring proof.
Tip/Trick: Claims answer “What are you trying to prove?”

x. Example of an assumption in renewable energy debates.

Answer: “Electric vehicles (EVs) are 100% eco-friendly.”
Hidden assumption: EV battery production/mining has no environmental cost.
Key Concept: Unverified premises weakening arguments.
Tip/Trick: Challenge assumptions with: “What evidence supports this?”

Summary Cheat Sheet

Concept	Core Idea	Red Flag
Cognitive Bias	Subjective thinking → errors	“I feel this is true”
False Cause	Sequence ≠ causation	“A happened, then B → A caused B”
Straw Man	Distort → attack	“So you’re saying [extreme]?”
Exclusion Fallacy	Hiding counter-evidence	Ignoring “inconvenient” data
Faulty Analogy	Weak comparisons	“It’s just like [unrelated]!”
Chemical Ethics	Balance innovation and safety	Absolute claims (“always safe”)
Scientific Claim	Assertion needing proof	Unsupported statements

Study Hack: Use real-world examples (e.g., Flint water crisis for regulation importance) to memorize concepts.

i. Explain confirmation bias and its potential impact on scientific research.

Statement:
Explain confirmation bias and its potential impact on scientific research.

Answer:
Confirmation bias is the tendency to favor, interpret, or recall information that confirms preexisting beliefs while ignoring or downplaying contradictory evidence. In scientific research, this manifests when researchers:

Selectively design experiments to yield expected results.
Overvalue data supporting their hypothesis and dismiss anomalies.
Cite only studies that align with their views during literature reviews.

Impact:

False Conclusions: Validates incorrect theories (e.g., linking vaccines to autism based on flawed data).
Wasted Resources: Diverts funding/time toward biased studies.
Erosion of Trust: Undermines scientific credibility when biases are exposed.

Key Concepts Used:

Cognitive psychology (information processing biases).
Scientific integrity (objectivity, reproducibility).
Research ethics (data transparency).

Tips and Tricks:

Red Flag: Ignoring “outlier” data.
Mitigation: Use blind trials, peer review, and preregistration of studies.
Example: In drug trials, confirmation bias might overstate efficacy by excluding non-responsive patients.

ii. Discuss ethical considerations in chemical production/use, balancing benefits and risks.

Statement:
Discuss the ethical considerations in the production and use of chemical substances, highlighting the balance between benefits and risks.

Answer:
Chemical ethics requires weighing societal benefits against health/environmental risks:

Benefits:

Life-saving drugs (e.g., antibiotics).
Food security (fertilizers/pesticides).

Risks:

Pollution (e.g., microplastics in oceans).
Health hazards (e.g., asbestos causing lung cancer).

Ethical Principles:

Precautionary Principle: Avoid chemicals with uncertain long-term effects.
Environmental Justice: Prevent disproportionate harm to marginalized communities (e.g., Flint water crisis).
Transparency: Disclose safety data (e.g., REACH regulations in the EU).

Balance Strategy:

Green Chemistry: Design biodegradable, low-toxicity alternatives.
Lifecycle Analysis: Assess environmental impact from production to disposal.

Key Concepts Used:

Risk-benefit analysis.
Stakeholder accountability (scientists, companies, regulators).
Sustainable development goals.

Tips and Tricks:

Framework: Use “People-Planet-Profit” to evaluate trade-offs.
Case Study: DDT boosted agriculture but caused ecological collapse → banned under Stockholm Convention.

iii. Deconstruct a scientific argument using EVs and air pollution.

Statement:
Deconstruct the structure of a scientific argument using the example of promoting electric vehicles to reduce air pollution.

Answer:

Component	Example for EVs
Claim	“Electric vehicles (EVs) reduce urban air pollution.”
Evidence	“EVs produce zero tailpipe emissions; gasoline cars emit CO₂, NOₓ, and particulates.”
Reasoning	“Transportation causes 60% of urban air pollution; replacing fossil-fuel vehicles cuts emissions.”
Counterclaim	“EV batteries require mining/power generation, shifting pollution elsewhere.”
Rebuttal	“Renewable-powered grids and battery recycling minimize net pollution (e.g., Tesla Gigafactories).”
Assumption	“EV adoption is scalable and infrastructure exists.”

Scientific Argument Structure:

Claim: Assertion requiring proof.
Evidence: Empirical data (emission studies).
Reasoning: Logical connection (pollution sources → solution).
Counter-Rebuttal: Addressing limitations.

Key Concepts Used:

Claim-evidence-reasoning framework.
Critical analysis of assumptions.
Holistic impact assessment.

Tips and Tricks:

Visualize: Create tables to map argument components.
Test Validity: Ask, “Does evidence directly support the claim?”

iv. Analyze regulations in the chemical industry with examples.

Statement:
Analyze the role of regulations and laws in ensuring ethical practices in the chemical industry, citing specific examples.

Answer:
Regulations enforce ethics through:

Risk Prevention:

REACH (EU): Requires safety assessments for chemicals; banned carcinogens like benzene in consumer products.

Accountability:

Bhopal Gas Tragedy (1984): Led to India’s Environment Protection Act, mandating disaster management plans.

Sustainability:

Montreal Protocol (1987): Phased out ozone-depleting CFCs, promoting safer refrigerants.

Impact:

Pros: Reduced pollution, safer workplaces, innovation in green chemistry.
Cons: Compliance costs; regulatory gaps in developing nations.

Key Concepts Used:

Regulatory frameworks (precautionary principle, polluter-pays).
Historical case studies.
Global vs. local governance.

Tips and Tricks:

Remember: Regulations = “Speed bumps for safety.”
Example Pairing:
Regulation: TSCA (USA)
Outcome: Banned PCBs in 1979 after proof of toxicity.

v. Evaluate pros/cons of pesticides in agriculture.

Statement:
Evaluate the pros and cons of using pesticides in agriculture, considering both human health and environmental impacts.

Answer:

Aspect	Pros	Cons
Human Health	↑ Food security (prevents famine)	Chronic diseases (cancer from glyphosate)
Environment	↑ Crop yields by 20-50%	Biodiversity loss (bees from neonicotinoids)
Economic	↓ Crop losses = affordable food	$15.6B/year in US health costs from exposure

Balanced Solutions:

Integrated Pest Management (IPM): Combine natural predators + minimal targeted pesticides.
Biodegradable Pesticides: e.g., Pyrethrins (plant-derived, low persistence).

Key Concepts Used:

Cost-benefit analysis.
Ecotoxicology (bioaccumulation, trophic cascades).
Sustainable agriculture.

Tips and Tricks:

Rule of Thumb: “No free lunch” – all chemicals have trade-offs.
Data Point: WHO estimates 3 million pesticide poisonings/year.

Summary Cheat Sheet

Question	Core Concept	Key Example
i	Bias → flawed research	Vaccine-autism retracted study
ii	Ethics = Benefit/Risk balance	DDT: malaria vs. ecosystem collapse
iii	Argument = Claim + Evidence + Reasoning	EV emissions reduction
iv	Regulations as safeguards	Bhopal → stricter laws
v	Pesticides: productivity vs. harm	Neonicotinoids and bee decline

Exam Strategy:

For ethics questions, always discuss trade-offs.
Use real-world examples to demonstrate depth (e.g., Flint for regulations, Silent Spring for pesticides).

Unit 2 Matter Solved Exercise 10th Federal board

June 11, 2025 by samreen

Short Questions

i. Explain why the temperature remains constant during the phase change from ice to water.

Answer:
The temperature remains constant during the melting of ice because the heat energy absorbed is used to break the intermolecular forces between solid particles instead of increasing kinetic energy.

Key Words Used:
Phase change, constant temperature, latent heat, intermolecular forces

ii. What is the name given to the phase change when a solid is converted directly to a gas?

Answer:
The process is called sublimation.

Key Words Used:
Sublimation, solid to gas, phase change

iii. What is the difference between evaporation and boiling?

Answer:
Evaporation occurs at any temperature from the surface of a liquid, while boiling occurs at a fixed temperature and throughout the liquid.

Key Words Used:
Evaporation, boiling, surface, fixed temperature

iv. Interpret a heating curve for water, identifying key phase changes.

Answer:
The heating curve shows temperature rising during solid, liquid, and gas phases, and remaining constant during melting and boiling points where phase changes occur.

Key Words Used:
Heating curve, melting point, boiling point, phase changes, temperature plateau

v. Explain the effect of increasing temperature on the pressure of a gas in a sealed container.

Answer:
Increasing temperature increases the kinetic energy of gas molecules, leading to more frequent and forceful collisions with the container walls, which increases pressure.

Key Words Used:
Kinetic energy, gas molecules, collisions, pressure increase, sealed container

vi. How does increasing the external pressure affect the boiling point of a liquid?

Answer:
Increasing external pressure raises the boiling point of a liquid because more energy is required for the vapor pressure to match the external pressure.

Key Words Used:
External pressure, boiling point, vapor pressure, energy requirement

vii. Describe how molecular mass influences the rate of diffusion.

Answer:
Gases with lower molecular mass diffuse faster than gases with higher molecular mass, as described by Graham’s law of diffusion.

Key Words Used:
Molecular mass, diffusion, Graham’s law, lighter gases

viii. Give an example of sublimation and explain its practical application.

Answer:
Example: Dry ice (solid CO₂) sublimates into gas.
Application: Used in fog machines and for preserving frozen items during shipping.

Key Words Used:
Sublimation, dry ice, fog machine, preservation

ix. Why is the diffusion of gases faster at higher temperatures?

Answer:
At higher temperatures, gas particles gain more kinetic energy and move faster, leading to a higher diffusion rate.

Key Words Used:
Kinetic energy, temperature, faster movement, diffusion rate

x. How does Avogadro’s law relate to the volume and number of moles of gas?

Answer:
Avogadro’s law states that equal volumes of gases at the same temperature and pressure contain an equal number of moles.

Key Words Used:
Avogadro’s law, volume, moles, temperature, pressure

Long Answer Questions

i. Describe in detail the kinetic particle theory and how it explains the phase changes of melting, freezing, boiling, and condensation.

Answer:
The kinetic particle theory explains that matter is made up of small particles (atoms or molecules) that are in constant motion. The behavior of these particles changes with temperature and energy:

Melting: When a solid is heated, its particles gain kinetic energy and vibrate more vigorously until they overcome the forces holding them together, causing a change to liquid.
Freezing: As a liquid cools, particles lose energy, move slower, and eventually arrange into fixed positions to form a solid.
Boiling: In liquids, increasing temperature causes particles to move faster. At the boiling point, particles throughout the liquid have enough energy to form gas bubbles and escape.
Condensation: When gas cools, particles lose kinetic energy, move closer together, and turn into liquid due to attractive forces.

Key Words Used:
Kinetic particle theory, motion, melting, freezing, boiling, condensation, energy, temperature, phase change

ii. Interpret a cooling curve, identifying and explaining the significance of the flat regions on the curve.

Answer:
A cooling curve shows how the temperature of a substance decreases over time as heat is removed. It consists of sloped and flat regions:

Sloped regions: Indicate temperature decrease in a single phase (e.g., gas cooling to liquid, or liquid cooling to solid).
Flat regions (plateaus): These occur during phase changes (condensation or freezing) where temperature remains constant even though heat is being removed. During this time, energy is released as intermolecular forces form.

Key Words Used:
Cooling curve, temperature, phase change, freezing, condensation, energy release, flat regions, heat removal

iii. Explain how diffusion works in gases and discuss the factors affecting the rate of diffusion, including molecular mass and temperature.

Answer:
Diffusion is the movement of gas particles from an area of high concentration to an area of low concentration, resulting in uniform distribution. In gases, particles move randomly and rapidly, allowing them to spread out and mix.

Factors affecting diffusion:

Molecular Mass: According to Graham’s law, lighter gases diffuse faster than heavier ones.
Temperature: Higher temperatures increase particle kinetic energy, which speeds up diffusion.
Pressure and Medium: Diffusion is faster at lower pressures and in less dense mediums.

Key Words Used:
Diffusion, gas particles, molecular mass, temperature, kinetic energy, Graham’s law, concentration gradient

🔍 THINK TANK Questions & Answers

1. Analyze the impact of altitude on the boiling point of water and how it affects cooking times. Provide a detailed explanation based on kinetic particle theory and external pressure.

Answer:
At higher altitudes, atmospheric pressure is lower. According to the kinetic particle theory, boiling occurs when the vapor pressure of a liquid equals the external (atmospheric) pressure. At high altitudes, water boils at a lower temperature because less energy is needed to match the reduced pressure. However, since the temperature is lower, cooking food (which relies on high-temperature boiling water) takes longer.

Example: At Mount Everest, water boils around 70°C, not 100°C, so food takes more time to cook.

Key Words Used:
Altitude, atmospheric pressure, vapor pressure, boiling point, kinetic particle theory, cooking time

2. Discuss the importance of understanding diffusion rates in the development of pharmaceuticals.

Answer:
Understanding diffusion rates is crucial in pharmaceutical development because drug molecules must diffuse through biological membranes (like cell walls) to reach their target sites. Faster diffusion means quicker drug action, which is vital for treatments like pain relief or emergency medication. Factors such as molecular size, solubility, and temperature influence diffusion.

Example: Inhalers for asthma use gases with high diffusion rates for rapid relief.

Key Words Used:
Diffusion, pharmaceuticals, membranes, drug delivery, molecular size, solubility, absorption

3. Evaluate the environmental and practical implications of using sublimation in various industries, such as air fresheners and 3D printing, considering both benefits and potential drawbacks.

Answer:
Sublimation is used in several industries due to its clean and residue-free phase change:

Benefits:
- Air fresheners: Use sublimation to slowly release fragrance into the air without melting.
- Freeze drying: Used in food and pharmaceuticals to preserve without heat damage.
- 3D Printing: Sublimation materials enable precise layer-by-layer building.
Drawbacks:
- Sublimation materials can be costly.
- Some sublimates (like dry ice) can cause environmental or safety issues if not handled properly.

Key Words Used:
Sublimation, industry, air freshener, 3D printing, freeze drying, environment, benefits, drawbacks

Ethics and Values in Chemistry: Unit 1 MCQs Solved | Federal Board FSc Part 2 New Book

June 11, 2025 by samreen

Question i:

Statement:
What is cognitive bias?

Options:
a) The process of making decisions based on logical reasoning.
b) The tendency to make decisions based on personal characteristics and beliefs.
c) The evaluation of arguments using empirical evidence.
d) The method of constructing arguments using logical fallacies.

Correct Answer:
b

Explanation:
Cognitive bias refers to systematic errors in thinking that arise from personal beliefs, experiences, or emotions, leading to irrational judgments. Option b is correct because cognitive biases stem from subjective influences (e.g., stereotypes, emotions) rather than objective analysis.

a is incorrect: Logical reasoning opposes cognitive bias, which is inherently illogical.
c is incorrect: Cognitive biases often ignore empirical evidence in favor of preconceived notions.
d is incorrect: Logical fallacies are flawed argument structures, while cognitive biases are unconscious mental shortcuts.

Tips and Tricks:

Key phrase: “tendency” – Cognitive biases are unconscious tendencies, not deliberate methods.
Remember: If an option describes objectivity (e.g., “logical reasoning,” “empirical evidence”), it likely contradicts cognitive bias.

Question ii:

Statement:
What is a hasty generalization fallacy?

Options:
a) Drawing a conclusion based on a large, representative sample.
b) Drawing a conclusion based on insufficient evidence.
c) Drawing a conclusion by misrepresenting an opponent’s argument.
d) Drawing a conclusion based on a false cause-and-effect relationship.

Correct Answer:
b

Explanation:
Hasty generalization occurs when a broad conclusion is made from inadequate or unrepresentative data. Option b directly defines this fallacy (e.g., “All crows are black” after seeing two crows).

a is incorrect: Large samples support reliable generalizations, making this the opposite of hasty generalization.
c describes the straw man fallacy.
d describes the post hoc fallacy.

Tips and Tricks:

Spot keywords: “insufficient evidence,” “small sample size,” or “jumping to conclusions.”
Avoid confusion: If an option mentions “large sample” (a) or “cause-and-effect” (d), it refers to other fallacies.

Question iii:

Statement:
What does the post hoc ergo propter hoc fallacy assume?

Options:
a) One event is caused by another simply because it follows it.
b) One event is unrelated to another.
c) One event is the result of a thorough investigation.
d) One event is part of a larger series of events.

Correct Answer:
a

Explanation:
The post hoc fallacy (Latin: “after this, therefore because of this”) assumes Event A causes Event B solely because B occurs after A (e.g., “I wore a red shirt, then my team won; therefore, my shirt caused the win”).

b is incorrect: The fallacy assumes a false connection, not unrelatedness.
c is incorrect: This describes evidence-based reasoning, not a fallacy.
d is incorrect: While events may be part of a series, post hoc specifically confuses sequence with causation.

Tips and Tricks:

Translate the Latin: Post hoc = “after this.” If the answer highlights temporal sequence as causation, it’s correct.
Real-world example: Superstitions (e.g., “I broke a mirror, then got into an accident; the mirror caused the accident”).

Question iv:

Statement:
Which fallacy involves attacking a distorted version of an opponent’s claim?

Options:
a) Confirmation Bias
b) Hasty Generalizations
c) The Straw Man Fallacy
d) Redefinition

Correct Answer:
c

Explanation:
The straw man fallacy misrepresents an opponent’s argument to make it easier to attack (e.g., oversimplifying “Reduce carbon emissions” to “You want to destroy the economy!”).

a is incorrect: Confirmation bias is seeking evidence to support preexisting beliefs, not misrepresenting arguments.
b is incorrect: Hasty generalization involves flawed sampling, not distortion of claims.
d is incorrect: Redefinition changes word meanings but isn’t a formal fallacy.

Tips and Tricks:

Visualize the name: A “straw man” is a weak dummy substitute for the real argument.
Identify distortion: If an option describes twisting or exaggerating an opponent’s view, it’s likely straw man.

Summary of Correct Answers:

Question	Correct Answer
i	b
ii	b
iii	a
iv	c

Key Study Tip: Memorize fallacies using real-life examples. For instance:

Cognitive bias → Believing a news article aligns with your views without fact-checking (confirmation bias).
Hasty generalization → “My neighbor’s dog bit me; all dogs are aggressive!”
Post hoc → “It rained after I washed my car; my car wash caused the rain.”
Straw man → “You support renewable energy? So you’d leave us all in the dark!”

Question iv:

Statement:
Which fallacy involves attacking a distorted version of an opponent’s claim?

Options:
a) Confirmation Bias
b) Hasty Generalizations
c) The Straw Man Fallacy
d) Redefinition

Correct Answer:
c) The Straw Man Fallacy

Explanation:
The Straw Man Fallacy occurs when someone misrepresents or oversimplifies an opponent’s argument to make it easier to attack. For example:

Original argument: “We should reduce fossil fuel use.”
Straw man distortion: “You want to ban all cars and destroy the economy!”
Why others are incorrect:
a) Confirmation bias involves favoring information that confirms preexisting beliefs.
b) Hasty generalizations draw conclusions from insufficient evidence.
d) Redefinition changes word meanings but isn’t a formal fallacy.

Tips and Tricks:

Visualize a “straw man” dummy: Attacking a weak, fake version of the real argument.
Key phrase: “distorted version” = immediate link to Straw Man.

Question v:

Statement:
What does the principle of Occam’s Razor advocate?

Options:
a) Choosing the most complex explanation for an event
b) Choosing the simplest explanation for an event
c) Choosing an explanation based on tradition
d) Choosing an explanation based on authority

Correct Answer:
b) Choosing the simplest explanation for an event

Explanation:
Occam’s Razor states that when multiple explanations exist, the one with the fewest assumptions is most likely correct. Simplicity minimizes unnecessary complexity.
Why others are incorrect:

a) Complexity often introduces unwarranted assumptions.
c) Tradition may perpetuate errors (e.g., appeal to tradition fallacy).
d) Authority doesn’t guarantee truth (e.g., appeal to authority fallacy).

Tips and Tricks:

Remember: “The simplest solution is usually the best.”
Example: Preferring gravity over invisible angels to explain falling objects.

Question vi:

Statement:
What is an example of the appeal to tradition fallacy?

Options:
a) Believing a theory is valid because an expert supports it
b) Believing a practice is correct because it has always been done that way
c) Believing an argument because it cannot be tested
d) Believing a hypothesis because it is the simplest explanation

Correct Answer:
b) Believing a practice is correct because it has always been done that way

Explanation:
Appeal to tradition assumes longevity implies validity (e.g., “Bloodletting works because doctors did it for centuries”).
Why others are incorrect:

a) Describes appeal to authority.
c) Relates to untestable claims, not tradition.
d) Describes Occam’s Razor.

Tips and Tricks:

Spot phrases like “we’ve always done this” or “it’s traditional.”
Tradition ≠ correctness (e.g., historical use of lead in makeup).

Question vii:

Statement:
Which of the following is a pro of chemical substances?

Options:
a) They always have a negative impact on health
b) They reduce carbon footprints through clean energy technologies
c) They are always safe for workers
d) They never cause environmental pollution

Correct Answer:
b) They reduce carbon footprints through clean energy technologies

Explanation:
Chemicals enable green technologies (e.g., lithium-ion batteries for electric cars, catalytic converters).
Why others are incorrect:

a) and d) use absolutes (“always,” “never”) – chemicals have nuanced impacts.
c) Safety depends on handling/regulations, not inherent properties.

Tips and Tricks:

Reject absolute terms; focus on context-specific benefits.
Link “clean energy” to chemical innovation (solar panels, biofuels).

Question viii:

Statement:
What is a con of weak or outdated regulations regarding chemicals?

Options:
a) They protect public health effectively
b) They foster innovation in chemical processes
c) They fail to address current risks
d) They reduce compliance costs for companies

Correct Answer:
c) They fail to address current risks

Explanation:
Outdated regulations ignore modern threats (e.g., nanoplastics, PFAS “forever chemicals”) due to evolving science.
Why others are incorrect:

a) Weak regulations endanger health.
b) Innovation requires safety frameworks to avoid disasters (e.g., Bhopal gas tragedy).
d) Reduced costs for companies ≠ public benefit.

Tips and Tricks:

“Fail to address” signals unmanaged dangers.
Historical cases: Asbestos regulations lagged decades behind evidence.

Question ix:

Statement:
What role do premises play in a scientific argument?

Options:
a) They oppose the main claim
b) They provide the foundation for the claim
c) They represent the conclusion
d) They are unsupported assumptions

Correct Answer:
b) They provide the foundation for the claim

Explanation:
Premises are evidence-based statements supporting a conclusion (e.g., “CO₂ traps heat [premise 1]; human activity emits CO₂ [premise 2] → thus, humans cause warming [claim]”).
Why others are incorrect:

a) Counterclaims oppose; premises support.
c) Conclusions follow from premises.
d) Premises should be empirically validated.

Tips and Tricks:

Premises = “building blocks” of arguments.
Test: “Does this statement back up the main idea?”

Question x:

Statement:
In the context of written articles, what would be a counterclaim for promoting electric vehicles?

Options:
a) Electric cars produce no emissions
b) Urban areas suffer from high air pollution
c) Electric cars still have high environmental costs due to battery production

Correct Answer:
c) Electric cars still have high environmental costs due to battery production

Explanation:
A counterclaim challenges the main argument. Promoting EVs often highlights zero tailpipe emissions (a), but battery production involves mining, energy use, and waste (c).
Why others are incorrect:

a) Supports EV promotion.
b) Justifies EVs as a solution to pollution.

Tips and Tricks:

Counterclaims introduce drawbacks/limitations.
Key conflict: “Environmental costs” vs. perceived sustainability.

Answer Summary:

Q	Correct	Key Concept
iv	c	Straw Man Fallacy
v	b	Occam’s Razor
vi	b	Appeal to Tradition
vii	b	Pros of Chemicals
viii	c	Regulation Cons
ix	b	Premises in Arguments
x	c	Counterclaims

Unit 2 Matter class 10th new Federal board Solved Mcqs

June 10, 2025 by samreen

MCQs with Answers and Explanations

1. When a gas changes directly into a solid, the process is called:

a) Evaporation
b) Condensation
c) Sublimation
d) Deposition ✅

Explanation:
Deposition is the direct conversion of a gas into a solid without passing through the liquid state (e.g., frost formation).

Tip:
Deposition is the reverse of sublimation. “Depo” = “down” to solid.

2. Which factor does NOT affect the rate of evaporation?

a) Surface area
b) Temperature
c) Humidity of air
d) Color of the liquid ✅

Explanation:
Evaporation depends on surface area, temperature, and air movement/humidity. The color of the liquid doesn’t affect evaporation.

Tip:
Focus on physical and environmental factors for evaporation—not aesthetic properties like color.

3. Which law explains that volume of a gas is inversely proportional to pressure at constant temperature?

a) Boyle’s Law ✅
b) Charles’s Law
c) Avogadro’s Law
d) Dalton’s Law

Explanation:
Boyle’s Law: P∝1/V when T is constant.

Tip:
Remember: Boyle = Pressure & Volume, and “Boil” compresses volume.

4. Which of the following occurs only at a fixed temperature?

a) Evaporation
b) Boiling ✅
c) Sublimation
d) Condensation

Explanation:
Boiling happens at the boiling point (fixed temperature). Evaporation occurs over a range of temperatures.

Tip:
Evaporation = surface phenomenon, Boiling = bulk and fixed temp.

5. When temperature of a gas increases at constant volume, its pressure:

a) Decreases
b) Increases ✅
c) Remains constant
d) Becomes zero

Explanation:
By Gay-Lussac’s Law, pressure is directly proportional to temperature at constant volume.

Tip:
Think of a pressure cooker: heat it, pressure rises!

6. Which of the following has the fastest rate of diffusion?

a) Oxygen
b) Carbon dioxide
c) Hydrogen ✅
d) Nitrogen

Explanation:
Rate of diffusion ∝ 1/Molar Mass. Hydrogen has the lowest molar mass → highest diffusion rate.

Tip:
Use Graham’s Law: lighter gas = faster diffusion.

Bonus Quick Trick Table

Process	Description	Trick to Remember
Sublimation	Solid → Gas	“Sub” up in smoke
Deposition	Gas → Solid	Gas “deposits” as solid
Boiling	Liquid → Gas (bulk)	Happens at boiling point
Evaporation	Liquid → Gas (surface)	Below boiling point
Condensation	Gas → Liquid	Think: cloud formation

MCQ 7: Kinetic Particle Theory and Pressure

Q7. According to kinetic molecular theory, why does the pressure of a gas increase when temperature increases (at constant volume)?

a) The volume increases
b) The particles move faster and hit the walls more frequently ✅
c) The number of particles increases
d) The particles get bigger

Answer: ✅ b) The particles move faster and hit the walls more frequently

Explanation:
As temperature increases, kinetic energy of gas particles increases. They move faster and collide more frequently and forcefully with the container walls, thus increasing pressure.

Tip:
Remember:

T↑ ⇒ KE↑ ⇒ Collisions↑ ⇒ Pressure↑
Think of a balloon in the sun—it expands due to pressure increase.

MCQ 8: Diffusion of Gases

Q8. Which factor affects the rate of diffusion of gases most significantly?

a) Molar mass of gas ✅
b) Color of gas
c) Amount of gas
d) Size of the container

Answer: ✅ a) Molar mass of gas

Explanation:
According to Graham’s Law, lighter gases diffuse faster than heavier ones. Rate ∝ 1/Molar mass

Tip:
Hydrogen diffuses faster than oxygen because it is lighter.
Use:

Rate1/Rate2=M2/M1

MCQ 9: Sublimation and Phase Change

Q9. Which everyday product uses sublimation?

a) Salt in water
b) Dry ice used in smoke machines ✅
c) Cooking oil
d) Ice cubes in freezer

Answer: ✅ b) Dry ice used in smoke machines

Explanation:
Dry ice (solid CO₂) skips the liquid phase and turns directly into gas—a classic example of sublimation.

Tip:
Sublimation = Substance skips liquid stage

🔍 Summary of Tips (7 to 9)

Concept	Tip / Mnemonic
Pressure ↑ with Temp ↑	Hotter gas = faster particles = more pressure
Diffusion	Lighter gas = faster diffusion (Graham’s Law)
Sublimation	Solid → Gas = “Sub” up in the air

Federal Board Class 10th Chemistry (New Book) – Chapter 1: History of Chemistry Exercise Solved

June 1, 2025 by samreen

MCQS

i. What is the principle of conservation of mass?

Options:
a) Mass is created during a chemical reaction
b) Mass is destroyed during a chemical reaction
c) Mass remains constant during a chemical reaction
d) Mass can be converted into energy

Answer:
c) Mass remains constant during a chemical reaction

Explanation:
The principle of conservation of mass states that mass is neither created nor destroyed in a chemical reaction; it is only rearranged. This was first formulated by Antoine Lavoisier.

Tips/Tricks:

Remember the phrase: “Matter cannot be created or destroyed.”
Eliminate options suggesting mass is created/destroyed (a, b). Option (d) refers to mass-energy equivalence (Einstein’s theory), which is not the conservation of mass.

ii. What does the peer review process ensure in scientific research?

Options:
a) Faster publication
b) Accuracy and validity of findings
c) Higher funding
d) Reduced experimentation

Answer:
b) Accuracy and validity of findings

Explanation:
Peer review involves evaluation by experts in the field to ensure the research is credible, methodologically sound, and free of errors before publication.

Tips/Tricks:

Focus on the purpose of peer review: quality control. Options (a), (c), and (d) are unrelated to its primary goal.

iii. Which of the following was an 18th-century chemical paradigm?

Options:
a) Atomic theory
b) Phlogiston theory
c) Quantum mechanics
d) Periodic table

Answer:
b) Phlogiston theory

Explanation:
The phlogiston theory (17th–18th century) proposed that a fire-like element (“phlogiston”) was released during combustion. It was later disproven by Lavoisier.

Tips/Tricks:

Note the time frame: “18th century.” Atomic theory (a) and the periodic table (d) emerged later. Quantum mechanics (c) is 20th-century.

iv. What does the periodic table of elements organize?

Options:
a) Elements by alphabetical order
b) Elements by their properties and atomic number
c) Elements by colour
d) Elements by discovery date

Answer:
b) Elements by their properties and atomic number

Explanation:
The periodic table arranges elements in order of increasing atomic number and groups them by similar chemical properties.

Tips/Tricks:

Recall that atomic number (proton count) is the primary organizing factor.

v. What does a 95% confidence level mean in scientific reporting?

Options:
a) Results are 95% accurate
b) There is a 5% chance the results are incorrect
c) 95% of scientists agree
d) The experiment is repeated 95 times

Answer:
b) There is a 5% chance the results are incorrect

Explanation:
A 95% confidence level means there is a 5% probability that the observed results occurred by random chance.

Tips/Tricks:

“Confidence level” relates to statistical probability, not accuracy (a) or consensus (c).

vi. Which model of the atom includes a central nucleus?

Options:
a) Plum-pudding model
b) Rutherford model
c) Bohr model
d) Quantum mechanical model

Answer:
b) Rutherford model

Explanation:
Rutherford’s gold foil experiment (1911) revealed the atom’s dense nucleus, replacing the plum-pudding model (a).

Tips/Tricks:

Bohr (c) and quantum models (d) came later and built on Rutherford’s nucleus discovery.

vii. What does repeatability in scientific experiments refer to?

Options:
a) Different results under the same conditions
b) Same results under the same conditions
c) Different methods
d) Multiple publications

Answer:
b) Same results under the same conditions

Explanation:
Repeatability means the same team can replicate results using identical methods and conditions.

Tips/Tricks:

“Repeat” = same conditions. “Reproducibility” (next question) involves different conditions.

viii. What is reproducibility in scientific experiments?

Options:
a) Different results under the same conditions
b) Same results using different methods
c) Results not verified
d) Repetition by the same scientist

Answer:
b) Same results using different methods

Explanation:
Reproducibility means independent teams can achieve similar results with different methods or setups.

Tips/Tricks:

Contrast with repeatability: reproducibility is broader (different labs/methods).

ix. What paradigm replaced the phlogiston theory?

Options:
a) Atomic theory
b) Theory of combustion
c) Quantum mechanics
d) Periodic table

Answer:
b) Theory of combustion

Explanation:
Lavoisier’s theory of combustion (involving oxygen) replaced the phlogiston theory in the late 18th century.

Tips/Tricks:

Link phlogiston to combustion. Atomic theory (a) and periodic table (d) are unrelated.

x. Which property does the periodic table help to predict?

Options:
a) Colour of elements
b) Properties of elements
c) Weight of elements
d) Discovery date of elements

Answer:
b) Properties of elements

Explanation:
The periodic table’s arrangement reveals trends in chemical properties (e.g., reactivity, electronegativity).

Tips/Tricks:

Focus on “properties,” as other options (a, c, d) are not primary purposes of the table.

Short Questions:

i. Explain the principle of conservation of mass in chemical reactions.

Answer:
The principle of conservation of mass states that mass is neither created nor destroyed in a chemical reaction. The total mass of the reactants (substances before the reaction) is always equal to the total mass of the products (substances after the reaction). This law was formulated by Antoine Lavoisier, who demonstrated it through experiments.

Example:
When magnesium burns in oxygen, the mass of magnesium oxide formed equals the combined mass of magnesium and oxygen used.

Key Points:

Mass remains constant.
Atoms are rearranged, not destroyed.
Lavoisier proved this through experiments.

ii. What is the role of empirical evidence in scientific research?

Answer:
Empirical evidence refers to data collected through observation and experimentation rather than just theories. It is crucial in science because:

Supports or disproves hypotheses – Scientists rely on experiments to verify ideas.
Ensures objectivity – Results must be measurable and repeatable.
Forms the basis of scientific laws – Repeated observations lead to established facts (e.g., conservation of mass).

Example:
Lavoisier’s experiments on combustion provided empirical evidence against the phlogiston theory.

iii. Describe the peer review process and its importance in science.

Answer:
The peer review process involves experts evaluating a scientific study before it is published.

Steps:

A scientist submits research to a journal.
Experts in the field review it for accuracy, validity, and methodology.
If approved, it is published; if not, corrections are suggested.

Importance:

Ensures high-quality, reliable research.
Prevents false or misleading claims.
Maintains trust in scientific knowledge.

iv. How did the phlogiston theory explain combustion?

Answer:
The phlogiston theory (17th–18th century) proposed that:

A fire-like substance called phlogiston was present in combustible materials.
During burning, phlogiston was released into the air.
Materials stopped burning when all phlogiston was gone.

Limitation:

It failed to explain why metals gained mass when burned (later explained by oxygen theory).

v. What is the significance of Rutherford’s model of the atom?

Answer:
Rutherford’s nuclear model (1911) was significant because:

It disproved the plum-pudding model (which said atoms were uniform).
It introduced the concept of a dense, positively charged nucleus.
It showed that most of the atom is empty space with electrons orbiting.

Experiment:
Gold foil experiment—alpha particles were deflected, proving the nucleus existed.

vi. How does the periodic table organize elements?

Answer:
The periodic table organizes elements by:

Atomic number (proton count) – Elements are arranged in increasing order.
Groups (columns) – Elements with similar properties (e.g., alkali metals in Group 1).
Periods (rows) – Shows trends like increasing reactivity.

Example:

Group 17 (Halogens): Highly reactive nonmetals (e.g., chlorine, fluorine).
Period 3: Contains sodium (Na), magnesium (Mg), etc.

vii. Define scientific paradigm with an example.

Answer:
A scientific paradigm is a widely accepted framework that guides research.

Example:

Phlogiston theory (old paradigm for combustion).
Oxygen theory (new paradigm by Lavoisier).

Key Idea:
When new evidence challenges a paradigm, a scientific revolution occurs (e.g., shift from phlogiston to oxygen).

viii. What does a confidence level in scientific research indicate?

Answer:
A confidence level (e.g., 95%) indicates:

The probability that results are not due to random chance.
A 95% confidence level means there is a 5% chance of error.
It helps scientists assess reliability (e.g., in drug trials).

Example:
If a study says “95% confidence,” it means the conclusion is likely correct 19 out of 20 times.

ix. Differentiate between repeatability and reproducibility in experiments.

Answer:

Repeatability	Reproducibility
Same results when the same scientist repeats the experiment under identical conditions.	Same results when different scientists repeat the experiment using different methods/labs.
Example: A chemist replicates their own experiment.	Example: Multiple labs confirm a discovery independently.

Importance:

Repeatability ensures consistency.
Reproducibility validates broader reliability.

x. Why is skepticism important in the scientific community?

Answer:
Skepticism is crucial because:

It prevents blind acceptance of claims without evidence.
Encourages testing and verification (e.g., debunking phlogiston theory).
Leads to better theories (e.g., oxygen replacing phlogiston).

Example:
Scientists questioned the phlogiston theory until Lavoisier provided better evidence for oxygen.

Long Questions:

Long Answer Questions (Detailed Solutions)

i. Transition from Phlogiston Theory to Oxygen Theory of Combustion

1. Phlogiston Theory (17th–18th Century)

Explanation:
Proposed by Georg Ernst Stahl.
Suggested that combustible materials contained “phlogiston” (a fire-like substance).
During burning, phlogiston was released into the air.
Limitations:
Could not explain why metals gained mass after burning (e.g., magnesium oxide).
Contradicted empirical evidence.

2. Oxygen Theory (Late 18th Century)

Lavoisier’s Contributions:
Demonstrated that combustion requires oxygen (not phlogiston).
Showed that metals combined with oxygen from the air, increasing their mass.
Introduced the law of conservation of mass.
Impact on Chemistry:
Disproved phlogiston theory, leading to modern chemical nomenclature.
Established quantitative methods in chemistry (measuring reactants/products).

3. Key Example:

Experiment: Heating mercury oxide produced oxygen, proving it was part of combustion.

Exam Tip: Focus on Lavoisier’s experiments and how they debunked phlogiston.

ii. Development of Atomic Models

1. Plum-Pudding Model (J.J. Thomson, 1897)

Description:
Atom as a “pudding” of positive charge with electrons embedded (like raisins).
Limitation: Could not explain atomic stability.

2. Rutherford’s Nuclear Model (1911)

Gold Foil Experiment:
Alpha particles deflected by a dense nucleus.
Proved atoms are mostly empty space.
Key Change: Introduced the central nucleus (protons + neutrons).

3. Bohr Model (1913)

Improvements:
Electrons orbit in fixed energy levels (shells).
Explained atomic spectra (e.g., hydrogen’s emission lines).

4. Quantum Mechanical Model (Modern Model)

Key Features:
Electrons exist in probability clouds (orbitals).
Uses quantum numbers to describe electron location.

Exam Tip: Compare each model’s strengths/weaknesses and experimental evidence.

iii. Periodic Table as a Paradigm in Chemistry

1. Organization Principles:

Atomic Number: Elements arranged by proton count.
Groups (Columns): Similar chemical properties (e.g., Group 1 = Alkali Metals).
Periods (Rows): Trends in reactivity and atomic size.

2. Predictive Power:

Mendeleev’s Predictions: Left gaps for undiscovered elements (e.g., gallium, germanium).
Modern Applications:
Predicts reactivity (e.g., fluorine = most reactive nonmetal).
Guides synthesis of new elements (e.g., synthetic elements like Tennessine).

3. Impact on Research:

Unified chemistry by classifying elements systematically.
Enabled discoveries like noble gases (Group 18).

Exam Tip: Highlight Mendeleev’s contributions and modern applications.

iv. Importance of Repeatability and Reproducibility

1. Definitions:

Repeatability: Same results under identical conditions (same lab).
Reproducibility: Same results under different conditions (other labs).

2. Role in Scientific Integrity:

Prevents Fraud: Ensures data is not fabricated (e.g., cold fusion controversy).
Validates Theories:
Example: Lavoisier’s experiments were repeated to confirm oxygen theory.
Failed Reproducibility: Phlogiston theory collapsed when others couldn’t verify it.

3. Case Study:

Millikan’s Oil Drop Experiment: Repeated globally to confirm electron charge.

Exam Tip: Contrast repeatability (same team) vs. reproducibility (independent teams).

v. Confidence Levels and Uncertainty in Chemistry Experiments

1. Definitions:

Confidence Level (e.g., 95%): Probability that results are not due to chance.
Uncertainty: Margin of error in measurements (e.g., ±0.01g).

2. Expression in Research:

Statistical Tools:
Standard deviation: Measures data spread.
p-value: Likelihood of observed results occurring randomly.
Example:
A drug trial with “95% confidence” means results are reliable 19/20 times.

3. Practical Example:

Titration Experiments:
Report average volume with ± uncertainty (e.g., 24.30 ± 0.05 mL).
Repeats reduce uncertainty.

Exam Tip: Link confidence levels to real chemistry experiments (e.g., titration).

Hydrogen Bonding MCQs with Answers & Explanations MDCAT practice

June 1, 2025 by samreen

1. Which of the following best explains why HF has a higher boiling point than HCl, despite HCl having a higher molecular weight?

A) HF has stronger London dispersion forces.
B) HF forms extensive hydrogen bonding, whereas HCl does not.
C) HCl is more polar than HF.
D) HF has a lower dipole moment than HCl.

Answer: B
Explanation: HF exhibits strong hydrogen bonding due to the high electronegativity of fluorine and the small size of hydrogen, leading to stronger intermolecular forces than HCl (which only has dipole-dipole interactions). London forces (A) are weaker in HF compared to HCl, but H-bonding dominates. Polarity (C) and dipole moment (D) are not the primary reasons for the boiling point difference.

2. In which of the following pairs is hydrogen bonding NOT possible?

A) H₂O and CH₃OH
B) NH₃ and CH₃NH₂
C) CH₄ and H₂
D) HF and HCOOH

Answer: C
Explanation: Hydrogen bonding requires a hydrogen atom covalently bonded to F, O, or N and a lone pair on another electronegative atom. CH₄ (methane) and H₂ lack both conditions, so no H-bonding occurs. All other options involve at least one H-bond donor (H attached to F/O/N) and acceptor (lone pair on F/O/N).

3. Why does formic acid (HCOOH) dimerize in the vapor phase, whereas acetic acid (CH₃COOH) forms longer chains?

A) Formic acid has stronger covalent bonds.
B) Steric hindrance in acetic acid prevents cyclic dimer formation.
C) Acetic acid has weaker hydrogen bonds.
D) Formic acid lacks a methyl group, allowing symmetric dimerization.

Answer: D
Explanation: Formic acid forms a cyclic dimer via two H-bonds, while acetic acid’s bulky methyl group disrupts this symmetry, leading to linear polymeric chains. Steric hindrance (B) is a factor, but the key difference is the absence of the methyl group in formic acid (D).

4. Which of the following has the highest strength of hydrogen bonding?

A) O–H···O (in water)
B) N–H···N (in ammonia)
C) F–H···F (in HF)
D) O–H···N (in water-ammonia mixtures)

Answer: C
Explanation: F–H···F is the strongest because fluorine is the most electronegative, creating the highest polarity and shortest bond length. The order of H-bond strength is typically F–H···F > O–H···O > N–H···N.

5. Ice floats on water because:

A) Hydrogen bonds in ice break upon melting.
B) Ice has a lower density due to an open hexagonal lattice stabilized by H-bonds.
C) Water molecules expand upon freezing.
D) Covalent bonds in ice are weaker than in liquid water.

Answer: B
Explanation: Ice has a hexagonal structure with H-bonds holding molecules farther apart than in liquid water, reducing density. (A) is incorrect because H-bonds persist in liquid water (but are more dynamic). (C) is partially true but not the primary reason. (D) is false—covalent bonds remain unchanged.

6. Which compound shows intramolecular hydrogen bonding?

A) Ethanol (C₂H₅OH)
B) Ortho-nitrophenol
C) Para-nitrophenol
D) Glycerol

Answer: B
Explanation: Ortho-nitrophenol forms an intramolecular H-bond between the –OH and –NO₂ groups, preventing intermolecular bonding. Para-nitrophenol (C) forms intermolecular H-bonds, while ethanol (A) and glycerol (D) only exhibit intermolecular H-bonding.

7. Why does NH₃ have a lower boiling point than H₂O despite both having hydrogen bonding?

A) NH₃ has weaker H-bonds due to lower electronegativity of N.
B) Water forms two H-bonds per molecule, while NH₃ forms only one.
C) NH₃ is lighter than H₂O.
D) Water has a bent structure, enhancing H-bonding.

Answer: A & D (Both are correct, but A is more fundamental)
Explanation: The electronegativity difference (O > N) makes O–H···O bonds stronger than N–H···N. Additionally, water’s bent structure allows for two H-bonds per molecule, whereas NH₃ forms only one. (C) is irrelevant because molecular weight is secondary to H-bond strength.

Transition Elements Solved Exercise PTB

December 28, 2024September 25, 2024 by samreen

Explore the solved exercise of Transition Elements from Punjab Textbook Board (PTB). Get detailed solutions, explanations, and notes tailored for college students to master key concepts of chemistry effectively.

Enhance your understanding of Transition Elements with this comprehensive solved exercise guide tailored for Punjab Textbook Board (PTB) students. Covering essential topics like electronic configurations, oxidation states, complex compounds, catalytic properties, and magnetic behavior, this guide provides step-by-step solutions to textbook exercises. Perfect for exam preparation, it includes solved MCQs, short questions, long questions, and conceptual problems. Aligned with the PTB syllabus, this resource simplifies the study of transition metals for easy learning and academic success.

(a) Binding energy
The binding energy of transition elements is influenced by the number of unpaired electrons in the d-orbitals. More unpaired electrons lead to stronger metallic bonds, increasing the binding energy.

Q.4 How does the electronic configuration of the valence shell affect the following properties of the transition elements?

(b) Paramagnetism
Paramagnetism in transition metals arises due to the presence of unpaired d-electrons. The more unpaired electrons there are, the stronger the paramagnetic property of the element.

(c) Melting points
The melting points of transition metals generally increase with the number of unpaired d-electrons, as this leads to stronger metallic bonding. However, this trend can vary across the series.

(d) Oxidation states
Transition elements exhibit variable oxidation states due to the similar energy levels of their 3d and 4s electrons. As the number of valence electrons available for bonding increases, the number of possible oxidation states also increases.

Q.5 Explain the following terms giving examples.

(a) Ligands
Ligands are ions or molecules that can donate a pair of electrons to the central metal atom/ion to form a coordination bond. Example: In [Cu(NH₃)₄]²⁺, ammonia (NH₃) acts as a ligand.

(b) Coordination sphere
The coordination sphere consists of the central metal atom/ion and the ligands directly attached to it. For example, in [Fe(CN)₆]⁴⁻, the coordination sphere is Fe and six cyanide ions (CN⁻).

(c) Substitutional alloy
A substitutional alloy forms when atoms of one element replace atoms of another element in a metal’s crystal lattice. Example: Brass is a substitutional alloy of copper and zinc.

(d) Central metal atom
The central metal atom is the atom in a coordination complex to which ligands are bonded. For example, in [Co(NH₃)₆]³⁺, cobalt (Co) is the central metal atom.

Q.6 Describe the rules for naming coordination complexes and give examples.

Answer:

Cation before anion: The name of the cationic part comes before the anionic part.
Ligands named first: Ligands are named before the central metal atom. Neutral ligands use their molecule name, while anionic ligands use the suffix ‘-o’.

Example: H₂O becomes aqua, NH₃ becomes ammine, Cl⁻ becomes chloro.

Number of ligands: Prefixes like mono-, di-, tri-, etc., indicate the number of each type of ligand.
Metal name: The metal is named, followed by its oxidation state in Roman numerals.

Example: [Cr(H₂O)₆]³⁺ is named as hexaaquachromium(III) ion.

For anionic complexes: The metal’s name ends with the suffix ‘-ate’.

Example: [Co(CN)₆]³⁻ is named as hexacyanocobaltate(III).

Q.7 What is the difference between wrought iron and steel? Explain the Bessemer’s process for the manufacture of steel.

Answer:

Wrought iron is a nearly pure form of iron with less than 0.08% carbon content, making it soft and malleable. It is used for decorative ironwork.
Steel contains more carbon (0.1% to 2%), making it stronger and harder than wrought iron. It is widely used in construction and manufacturing.

Bessemer’s process:
The Bessemer process is a method for making steel by blowing air through molten pig iron to oxidize and remove impurities like carbon, silicon, and manganese. The process helps in producing steel rapidly and at a lower cost.

Q.8 Explain the following giving reasons.

(a) Why does damaged tin-plated iron get rusted quickly?
Answer: When tin-plated iron is damaged, the exposed iron reacts with water and oxygen, forming rust. Since tin is less reactive than iron, the iron oxidizes (rusts) faster when exposed in the presence of tin, acting as a sacrificial element.

(b) Under what conditions does aluminum corrode?
Answer: Aluminum corrodes when exposed to moist environments containing salts or acids. However, aluminum forms a protective layer of aluminum oxide (Al₂O₃) that prevents further corrosion under normal conditions.

(c) How does the process of galvanizing protect iron from rusting?
Answer: Galvanizing involves coating iron with a layer of zinc. Zinc acts as a sacrificial anode, meaning it corrodes in place of the iron. Even if the zinc coating is damaged, the exposed iron remains protected as the zinc continues to corrode preferentially.

Q.9 How chromate ions are converted into dichromate ions?

Answer:
Chromate ions CrO42- are converted into dichromate ions Cr2O7^2- in acidic conditions by the following equilibrium reaction:

2 CrO4^2- + 2 H^+ → Cr2O72- + H2O

This conversion involves the protonation of chromate ions, leading to the formation of dichromate ions.

Q.10 Describe the preparation of KMnO₄ and K₂CrO₄.

Answer:

Preparation of Potassium Permanganate (KMnO₄):

Oxidation of Manganese Dioxide (MnO₂): Manganese dioxide is fused with potassium hydroxide (KOH) in the presence of an oxidizing agent like potassium nitrate (KNO₃):
2 MnO2 + 4 KOH + O2 → 2 K2MnO4 + 2 H2O
Conversion of Potassium Manganate to Potassium Permanganate: Potassium manganate ((K_2MnO_4)) is oxidized in an acidic or neutral medium to form potassium permanganate:
3 K2MnO4 + 2 H2O → 2 KMnO4 + MnO2 + 4 KOH

Preparation of Potassium Chromate (K₂CrO₄):

Oxidation of Chromite Ore (FeCr₂O₄): Chromite ore is heated with sodium carbonate (Na₂CO₃) in the presence of air or oxygen, yielding sodium chromate ((Na₂CrO₄)):
4 FeCr2O4 + 8 Na2CO3 + 7 O2 → 8 Na2CrO4 + 2 Fe2O3 + 8 CO2
Conversion to Potassium Chromate: Sodium chromate is treated with potassium chloride (KCl), forming potassium chromate:
Na2CrO4 + 2 KCl → K2CrO4 + 2 NaCl

Q.11 Give systematic names to the following complexes:

(a) [Fe(CO)₅]
Answer: Pentacarbonyliron(0)

(b) [Co(NH₃)₆]Cl₃
Answer: Hexaamminecobalt(III) chloride

(c) [Fe(H₂O)₆]²⁺
Answer: Hexaaquairon(II) ion

(d) Na₃[CoF₆]
Answer: Sodium hexafluorocobaltate(III)

(e) K₃[Cu(CN)₄]
Answer: Potassium tetracyanocuprate(I)

(f) K₂[PtCl₆]
Answer: Potassium hexachloroplatinate(IV)

(g) [Pt(OH)₂(NH₃)₄]SO₄
Answer: Tetraamminehydroxoplatinum(IV) sulfate

(h) [Cr(OH)₃(H₂O)₃]
Answer: Trihydroxotriaquachromium(III)