SLO-based exercises

Chapter 4 Stoichiometry SLO based solved Exercise 9th class new syllabus

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Get comprehensive solutions for Chapter 4 Stoichiometry from the 9th Class New Syllabus. This SLO-based solved exercise is designed to help students master the concepts of stoichiometry effectively.

(i) How many atoms are present in one gram of H2O?

1 mole of H2O = 18 g and contains 6.022×1023 molecules.
1 molecule of H2O = 3 atoms (2 H + 1 O).

Thus,
Atoms in 1 gram of H2O: 6.022×1023/18×3≈10.02×1022

Correct answer: (a) 10.02×1022 atoms

(ii) Which is the correct formula of calcium phosphide?

The formula of calcium phosphide is based on the charges of Ca2+ and P3−. To balance charges, the formula is Ca3P2

Correct answer: (c) Ca3P2

(iii) How many atomic mass units (amu) are there in one gram?

1 amu = 1.66×10−24g.

Number of amu in 1 g=1/1.66×10−24≈6.022×1023

Correct answer: (b) 6.022×1023

(iv) Structural formula of 2-hexene is CH3−CH=CH−(CH2)2−CH3. What is its empirical formula?

The molecular formula of 2-hexene is C6H12
Empirical formula is obtained by dividing subscripts by their greatest common divisor (6). Empirical formula=CH2

Correct answer: (b) CH2

(v) How many moles are there in 25 g of H2SO4?

Molar mass of H2SO4 = 2+32+(4×16)=98 g/mol

Moles=Mass/Molar mass=25/98≈0.255 moles.

Correct answer: (c) 0.255 moles

(vi) A necklace has 6 g of diamonds in it. What are the number of carbon atoms in it?

Diamonds are made of carbon.
Molar mass of carbon = 12 g/mol.
Number of moles of carbon: Moles=6/12=0.5 moles

Number of carbon atoms: 0.5×6.022×1023≈3.01×1023

Correct answer: (d) 3.01×1023

(vii) What is the mass of Al in 204 g of aluminum oxide (Al2O3)?

Molar mass of Al2O3 = 2(27)+3(16)=102 g/mol
Mass fraction of Al: 2(27)/102=54/102=0.5294

Mass of Al in 204 g of Al2O3: 0.5294×204≈108 g

Correct answer: (d) 108 g

(viii) Which one of the following compounds will have the highest percentage by mass of nitrogen?

  • For CO(NH2)2(urea):
    Molar mass = 12+16+2(14)+4(1)=60
    Nitrogen mass = 28
    Percentage of N = 28/60×100=46.67%
  • For NH4NO3:
    Molar mass = 14+4+14+3(16)=80
    Nitrogen mass = 28.
    Percentage of N = 28/80×100=35%

Correct answer: (a) CO(NH2)2

(ix) When one mole of each of the following compounds is reacted with oxygen, which will produce the maximum amount of CO2?

The number of moles of CO2 depends on the number of carbon atoms in the compound. Among the given options:

  • Methane (CH4): Produces 1 mole of CO2.
  • Ethane (C2H6): Produces 2 moles of CO2.
  • Diamond (C): Produces 1 mole of CO2

Correct answer: (b) Ethane

(x) What mass of 95% Ca(OH)2 will be required to neutralize 50 cm3 of 0.5 M H2SO4?

  • Reaction: Ca(OH)2+H2SO4→CaSO4+2H2O
    1 mole of H2SO4 reacts with 1 mole of Ca(OH)2.
    Moles of H2SO4: 0.5×0.05=0.025 moles
    Mass of pure Ca(OH)2: 0.025×(40+2(16+1))=0.025×74=1.85 g.
  • Mass of 95% pure Ca(OH)2: 1.850.95≈1.95 g

Correct answer: (d) 1.95 g

2. Questions for Short Answers

i. Write down the chemical formula of barium nitride.
The chemical formula of barium nitride is Ba₃N₂.
Explanation: Barium (Ba) is an alkaline earth metal with a +2 oxidation state, and nitride (N) is a nonmetal with a -3 charge. To balance the charges, three barium ions combine with two nitride ions, forming Ba₃N₂.

ii. Find out the molecular formula of a compound whose empirical formula is CH₂O and its molar mass is 180.
Step 1: Calculate the molar mass of the empirical formula (CH₂O).
Molar mass of CH₂O = 12 (C) + 2(1) (H) + 16 (O) = 30 g/mol.

Step 2: Determine the ratio of the molecular formula to the empirical formula.
Ratio=Molar mass of compound / Molar mass of empirical formula=180/30=6.

Step 3: Multiply the empirical formula by the ratio.
Molecular formula = (CH2O)6=C6H12O6 = C₆H₁₂O₆.
The molecular formula of the compound is C₆H₁₂O₆ (glucose).

iii. How many molecules are present in 1.5 g H₂O?
Step 1: Calculate the molar mass of water (H₂O).
Molar mass = 2(1) + 16 = 18 g/mol.

Step 2: Find the number of moles in 1.5 g of H₂O.
Moles = Mass/Molar mass=1.5/18=0.0833 mol

Step 3: Calculate the number of molecules using Avogadro’s number (6.022×1023 molecules/mol)
Number of molecules = 0.0833×6.022×1023=5.02×1022
Thus, there are approximately 5.02×1022

iv. What is the difference between a mole and Avogadro’s number?

  • Mole: A mole is a unit in chemistry that represents a quantity of substance. One mole of any substance contains the same number of particles (atoms, molecules, or ions) as there are in 12 g of carbon-12.
  • Avogadro’s Number: Avogadro’s number is a constant that defines the number of particles in one mole of a substance. It is equal to 6.022×1023 particles/mol

Difference: The mole is a quantity (like a dozen), while Avogadro’s number provides the specific count of particles in one mole.

v. Write down the chemical equation for the given reaction.
Copper + Sulphuric acid → Copper sulphate + Sulphur dioxide + Water
Balanced chemical equation:
Cu+2H₂SO₄→CuSO₄+SO₂+2H₂O

3. Constructed Response Questions

i. Different compounds will never have the same molecular formula but can have the same empirical formula. Explain.

  • The empirical formula represents the simplest whole-number ratio of elements in a compound, whereas the molecular formula shows the exact number of atoms of each element in a molecule.
  • Example: Acetic acid (C₂H₄O₂) and glucose (C₆H₁₂O₆) have the same empirical formula (CH₂O), but their molecular formulas are different.
  • Explanation: Compounds with different molecular structures can share the same empirical formula because the molecular formula is a multiple of the empirical formula.

ii. Write down the chemical formulas of the following compounds.

  1. Calcium phosphate: Ca₃(PO₄)₂
  2. Aluminium nitride: AlN
  3. Sodium acetate: CH₃COONa
  4. Ammonium carbonate: (NH₄)₂CO₃
  5. Bismuth sulphate: Bi₂(SO₄)₃

iii. Why does Avogadro’s number have immense importance in chemistry?
Avogadro’s number (6.022×1023 is essential in chemistry because:

  • It establishes a connection between the microscopic (atoms/molecules) and macroscopic (grams/moles) scales.
  • It allows chemists to calculate the number of particles in a given mass of substance.
  • It is crucial for determining stoichiometric relationships in chemical reactions, enabling precise calculations for reactants and products.

iv. When 8.657 g of a compound were converted into elements, it gave 5.217 g of carbon, 0.962 g of hydrogen, and 2.478 g of oxygen. Calculate the percentage of each element present in this compound.
Step 1: Calculate the total mass of the compound.
Total mass = 5.217+0.962+2.478=8.657 g

Step 2: Calculate the percentage of each element.

  • Carbon: 5.2178.657×100=60.3%
  • Hydrogen: 0.9628.657×100=11.1%
  • Oxygen: 2.4788.657×100=28.6%

Thus, the percentages are:

  • Carbon: 60.3%
  • Hydrogen: 11.1%
  • Oxygen: 28.6%.

4. Descriptive Questions

i. Which conditions must be fulfilled before writing a chemical equation for a reaction?
To write a chemical equation, the following conditions must be fulfilled:

  1. Correct identification of reactants and products: Ensure the substances involved in the reaction are accurately identified.
  2. Balancing the equation: The equation must follow the law of conservation of mass, where the number of atoms for each element is the same on both sides.
  3. Physical states of substances: Indicate the physical states of reactants and products (solid (s), liquid (l), gas (g), or aqueous (aq)).
  4. Reaction conditions: Specify the conditions such as temperature, pressure, or the use of catalysts if required for the reaction.

ii. Explain the concepts of Avogadro’s number and mole.

  • Avogadro’s Number: Avogadro’s number (6.022×1023 is the number of particles (atoms, molecules, or ions) in one mole of a substance. It bridges the gap between the microscopic scale and the macroscopic scale.
  • Mole: A mole is a unit of measurement used in chemistry to represent 6.022×1023 particles of a substance. It is the amount of a substance that contains as many entities as there are atoms in 12 grams of carbon-12.

iii. How many grams of CO₂ will be produced when we react 10 g of CH₄ with excess of O₂ according to the following equation?
CH4+2O2→CO2+2H2OCH₄ + 2O₂ → CO₂ + 2H₂O

  1. Molar masses:
    • CH₄ = 16 g/mol
    • CO₂ = 44 g/mol
  2. Moles of CH₄:
    Moles = Mass/Molar mass=10/16=0.625 mol
  3. Moles of CO₂:
    From the equation, 1 mole of CH₄ produces 1 mole of CO₂.
    Moles of CO₂ = 0.625 mol.
  4. Mass of CO₂:
    Mass = Moles × Molar mass = 0.625×44=27.5 g

Answer: 27.5 g of CO₂ will be produced.

iv. How many moles of coal are needed to produce 10 moles of CO according to the following equation?
3C+O2+H2O→H2+3CO3C + O₂ + H₂O → H₂ + 3CO

From the equation, 3 moles of carbon (C) produce 3 moles of CO.
Thus, to produce 10 moles of CO: Moles of coal=103=3.33 moles.\text{Moles of coal} = \frac{10}{3} = 3.33 \, \text{moles}.

Answer: 3.33 moles of coal are needed.

v. How much SO₂ is needed in grams to produce 10 moles of sulphur?
2H2S+SO2→2H2O+3S

From the equation, 1 mole of SO₂ produces 1.5 moles of sulphur.
To produce 10 moles of sulphur: Moles of SO₂=10/1.5=6.67 moles

Molar mass of SO₂ = 32 (S) + 2(16) = 64 g/mol.
Mass = Moles × Molar mass = 6.67×64=426.88 g

Answer: 426.88 g of SO₂ are needed.

vi. How much ammonia is needed in grams to produce 1 kg of urea fertilizer?
2NH3+CO2→CO(NH2)2+H2O

  1. Molar masses:
    • NH₃ = 17 g/mol
    • CO(NH₂)₂ (urea) = 60 g/mol
  2. Moles of urea:
    Moles = Mass/Molar mass=1000/60=16.67 mol
  3. Moles of NH₃:
    From the equation, 2 moles of NH₃ produce 1 mole of urea.
    Moles of NH₃ = 16.67×2=33.34 mol.
  4. Mass of NH₃:
    Mass = Moles × Molar mass = 33.34×17=566.78 g

Answer: 566.78 g of ammonia is needed.

vii. Calculate the number of atoms in the following:

(a) 3 g of H₂:
Moles of H₂ = Mass/Molar mass=3/2=1.5 mol
Number of molecules = 1.5×6.022×1023=9.033×1023
Each molecule of H₂ contains 2 atoms, so:
Number of atoms = 9.033×1023×2=1.8066×1024
Number of molecules = 3.4×6.022×1023=2.0475×1024
Each molecule of N₂ contains 2 atoms, so:
Number of atoms = 2.0475×1024×2=4.095×1024
Molar mass of C₆H₁₂O₆ = 6(12)+12(1)+6(16)=180 g/mol
Number of molecules = 0.0556×6.022×1023=3.348×1022
Each molecule contains 6+12+6=246 + 12 + 6 = 24 atoms.
Number of atoms = 3.348×1022×24=8.035×1023

5. Investigative Questions

i. How many moles of water are needed for a single adult?
Volume of water per glass = 400 cm3
Density of water = 1 g/cm3
Mass of water = 400×8=3200 g

Molar mass of water = 18 g/mol.
Moles of water = Mass/Molar mass=3200/18=177.78 mol

Answer: 177.78 moles of water are needed.

ii. How many moles of SiO₂ are present in the glass?
Assuming the mass of glass is provided, moles = Mass of glass/Molar mass of SiO₂

where Molar mass of SiO₂=28+2(16)=60 g/mol

State of matter and phase changes new book slo base exercise solved

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solved exercises based on the new SLO (Student Learning Outcomes) syllabus for “State of Matter and Phase Changes.” This comprehensive guide includes detailed solutions, simple explanations, and key concepts to help students master the topic effectively.

(i) Matter is present in neon signs in the state of:

  • Options: (a) Supercritical fluid
    (b) Plasma
    (c) Gas
    (d) Liquid crystal
  • Correct Answer: (b) Plasma
  • Explanation:
    Neon signs operate by ionizing neon gas with electricity. This ionization creates plasma, a state of matter consisting of freely moving electrons and ions that emit light.

(ii) Hazardous effects of shopping bags are studied in:

  • Options: (a) Geochemistry
    (b) Inorganic chemistry
    (c) Analytical Chemistry
    (d) Environmental Chemistry
  • Correct Answer: (d) Environmental Chemistry
  • Explanation:
    Environmental chemistry studies chemical processes in the environment, including pollution and the non-biodegradability of plastic shopping bags.

(iii) The man-made polymer is:

  • Options: (a) Starch
    (b) Polystyrene
    (c) Protein
    (d) Cellulose
  • Correct Answer: (b) Polystyrene
  • Explanation:
    Polystyrene is a synthetic polymer used in packaging materials. Starch and cellulose are natural biopolymers, and protein is a natural macromolecule.

(iv) The allotropic form of sulfur is:

  • Options: (a) Brass
    (b) Rhombic
    (c) Graphite
    (d) Bronze
  • Correct Answer: (b) Rhombic
  • Explanation:
    Rhombic sulfur is the most stable crystalline form of sulfur. Brass and bronze are alloys, and graphite is an allotrope of carbon.

(v) Which liquid among the following is a colloidal solution?

  • Options: (a) Milk
    (b) Slaked lime used for whitewash
    (c) Vinegar solution
    (d) Mixture of AgCl in water
  • Correct Answer: (a) Milk
  • Explanation:
    Milk is a colloid where fat droplets are dispersed in water. Slaked lime is a suspension, vinegar is a true solution, and AgCl forms a precipitate in water.

(vi) Which of the following is a heterogeneous mixture?

  • Options: (a) A solution of calcium in hydroxide water
    (b) A solution of potassium nitrate in water
    (c) Hot chocolate
    (d) Concrete mixture
  • Correct Answer: (d) Concrete mixture
  • Explanation:
    Heterogeneous mixtures have non-uniform compositions. Concrete is an example, with distinct phases of sand, cement, and water. The other options are homogeneous mixtures.

(vii) A state of matter whose properties are between those of liquids and crystalline solids:

  • Options: (a) Liquid crystal
    (b) Supercritical fluid
    (c) Plasma
    (d) Dark matter
  • Correct Answer: (a) Liquid crystal
  • Explanation:
    Liquid crystals have properties of both liquids (flow) and solids (ordered molecular structure). They are commonly used in LCDs.

(viii) When the tiny particles of a substance are dispersed through a medium, the mixture is named as:

  • Options: (a) True solution
    (b) Colloid
    (c) Suspension
    (d) Heterogeneous mixture
  • Correct Answer: (b) Colloid
  • Explanation:
    A colloid is a mixture where particles are small enough to stay dispersed and not settle, like in milk or fog. Suspensions have larger particles that settle, and true solutions are homogeneous.

(ix) A solution of KClO3 has a solubility of about 13.2g per 100 cm³ at 40∘C. How will its solubility be affected if you decrease the temperature?


Options:
(a) The solubility will increase.
(b) The solubility will decrease.
(c) The solubility will remain the same.
(d) The solubility will first increase with temperature and then it will decrease.

Correct Answer: (b) The solubility will decrease.
Explanation: Solubility of most solid solutes, such as KClO3, decreases with a decrease in temperature because solubility depends on the kinetic energy of particles, which is reduced at lower temperatures.

(x) You are studying the rate of hydrolysis of organic compound starch under different conditions of temperature. In which branch of chemistry will this topic fall?


Options:
(a) Organic Chemistry
(b) Analytical Chemistry
(c) Biochemistry
(d) Physical Chemistry

Correct Answer: (d) Physical Chemistry
Explanation: Physical chemistry deals with studying the rate of chemical reactions and how external factors, such as temperature, influence these reactions. Hydrolysis of starch involves the study of reaction rates under physical conditions.

Short Answer Questions

1. Why is there a need to divide Chemistry into many branches? Give three reasons.
Answer: Chemistry is divided into branches to make it easier to study and apply:

  1. Specialization: Each branch focuses on a specific area, like organic chemistry studies carbon compounds, while analytical chemistry deals with testing and measurements.
  2. Understanding Complexity: Different chemical reactions and processes are complex and require specialized study.
  3. Practical Applications: Dividing chemistry allows us to apply knowledge to specific fields, such as medicine (biochemistry) or materials science (physical chemistry).

2. Reactions may take place due to electrons outside the nucleus or inside the nucleus. Which branches of chemistry cover these two types of reactions?
Answer:

  1. Electron-based reactions: These are covered in branches like organic and inorganic chemistry. They involve the sharing or transfer of electrons.
  2. Nuclear-based reactions: These are covered in nuclear chemistry, which studies changes within the nucleus, such as radioactive decay or fission.

3. What types of problems are solved in analytical chemistry?
Answer: Analytical chemistry solves problems related to:

  • Identifying the composition of unknown substances.
  • Determining the concentration of specific chemicals in a sample.
  • Monitoring the quality and purity of materials in industries.

4. Both graphite and graphene have hexagonal layered structures. What is the difference?
Answer:

  • Graphite: Consists of multiple layers of carbon atoms arranged in hexagonal structures. The layers are weakly bonded, making graphite soft and slippery.
  • Graphene: Consists of a single layer of carbon atoms in a hexagonal structure. It is stronger, more conductive, and lightweight compared to graphite.

5. Why are supercritical fluids important?
Answer: Supercritical fluids (like carbon dioxide at high pressure) are important because:

  • They are used as solvents in chemical processes.
  • They allow for efficient extraction of compounds (e.g., caffeine from coffee).
  • They are environmentally friendly compared to conventional solvents.

6. In which state does matter exist in the Sun?
Answer: Matter in the Sun exists in the plasma state, where atoms are ionized into positive ions and free electrons due to extremely high temperatures.

7. What is the importance of graphene?
Answer: Graphene is important because it:

  • Has excellent electrical conductivity, making it useful in electronics.
  • Is extremely strong yet lightweight, used in materials science.
  • Has potential applications in energy storage, sensors, and medicine.

8. Which form of matter do most of the material things in this world belong to?
Answer: Most materials in the world are in the solid state, where atoms are tightly packed and maintain a fixed shape.

Constructed Response Questions

1. How does a supercritical state look like?
Answer: A supercritical state is a phase where a substance behaves like both a gas and a liquid. It has no distinct boundary between liquid and gas phases and is often clear and dense, like a thick gas.

2. In what way is plasma created in a fluorescent tube?
Answer: In a fluorescent tube:

  • Electric current flows through low-pressure gas (like mercury vapor).
  • The energy excites the gas atoms, ionizing them into plasma, emitting ultraviolet light.
  • This UV light interacts with the phosphor coating inside the tube, producing visible light.

3. Most of the molecules we study in biochemistry are organic in nature. Where does the difference exist in organic and biochemistry branches of chemistry?
Answer:

  • Organic Chemistry: Focuses on all carbon-containing compounds, whether living or non-living.
  • Biochemistry: Studies chemical processes and compounds specific to living organisms, like enzymes and DNA.

4. Give the reason for the brilliance shown by a diamond. Can you improve it?
Answer: Diamonds show brilliance because:

  • They have a high refractive index, bending light multiple times inside the crystal.
  • Light reflects and refracts, creating sparkle.
    Improvement: Brilliance can be enhanced by cutting the diamond precisely to optimize light reflection.

5. Explain the dissolution of NaCl in water.
Answer:
When NaCl dissolves in water:

  • Water molecules surround Na⁺ and Cl⁻ ions due to their polarity.
  • The positive side of water (H⁺) attracts Cl⁻ ions, and the negative side (O⁻) attracts Na⁺ ions.
  • These ions are separated and evenly distributed in the water, forming a solution.

Short Questions

6. Why do different compounds have different solubilities in water at a particular temperature?
Answer: Different compounds have different solubilities because:

  • Their molecular structures and forces vary (ionic, covalent, or hydrogen bonding).
  • The temperature affects how much energy is available to break bonds between molecules.
  • The nature of the solvent (like water being polar) interacts differently with solutes.

7. Why can NaCl be crystallized from water just like KNO3?
Answer: Both NaCl and KNO3 dissolve in water to form a solution. By cooling the solution or evaporating water, the solubility decreases, and the ions come together to form crystals.

8. Why is graphite slippery to touch? What property of graphite enables it to be used as a lubricant?
Answer:

  • Graphite is slippery because its carbon atoms form layers that slide over each other easily due to weak forces between them.
  • This property makes it an excellent lubricant, reducing friction in machinery.

Descriptive Questions

1. Mention the branch of Chemistry for each topic:
(a) Rate of a reaction: Physical Chemistry (studies reaction rates and factors affecting them).
(b) Digestion of food in the human body: Biochemistry (focuses on chemical processes in living organisms).
(c) Properties of plasma: Physical Chemistry (examines the fourth state of matter).
(d) Ecosystem: Environmental Chemistry (studies the chemical processes affecting ecosystems).
(e) Reactions during fireworks: Inorganic Chemistry (explains reactions involving metals and salts).
(f) Measurement of absorption of wavelengths: Analytical Chemistry (focuses on spectroscopic techniques).

2. What are allotropic forms? Explain the allotropic forms of carbon and sulfur. How does coal differ from diamond?
Answer:

  • Allotropes: Different physical forms of the same element, having different structures.
  • Carbon Allotropes:
    • Diamond: Hard, transparent, with a 3D rigid structure.
    • Graphite: Soft, slippery, made of layers.
    • Fullerene: Spherical molecules (like a ball).
  • Sulfur Allotropes:
    • Rhombic Sulfur: Solid at room temperature.
    • Monoclinic Sulfur: Forms at higher temperatures.
  • Coal vs. Diamond:
    • Coal: Impure, made of carbon with other substances.
    • Diamond: Pure carbon in a crystalline form with strong covalent bonds.

3. What are supercritical fluids? How are they different from ordinary liquids?
Answer:

  • Supercritical Fluids: Substances at a temperature and pressure where they have properties of both gases and liquids.
  • Difference:
    • Supercritical fluids are denser than gases but flow like liquids.
    • They are used as solvents (e.g., in caffeine extraction).

4. Define solubility of a solute. How does the solubility of solutes change with temperature?
Answer:

  • Solubility: The maximum amount of solute that can dissolve in a solvent at a specific temperature.
  • Effect of Temperature:
    • For solids: Solubility increases with temperature.
    • For gases: Solubility decreases as temperature rises.

5. What types of movements are present in gaseous and liquid molecules?
Answer:

  • Gases: Molecules move freely in all directions with high speed (random motion).
  • Liquids: Molecules move slower than gases and can slide past each other (flow).

6. Differentiate between inorganic and organic chemistry.
Answer:

  • Organic Chemistry: Studies compounds containing carbon (e.g., fuels, plastics).
  • Inorganic Chemistry: Studies compounds without carbon (e.g., salts, metals).

Investigative Questions

1. Describe the process in which potassium nitrate is purified by crystallizing it in water.
Answer:

  1. Dissolve KNO3 in hot water to make a saturated solution.
  2. Filter the solution to remove impurities.
  3. Allow the solution to cool slowly.
  4. KNO3 crystals form as the solubility decreases.
  5. Separate the crystals and dry them.

2. Graphene is called a miracle material. Which of its properties makes it very useful in electronics?
Answer:
Graphene is highly useful in electronics because:

  • It is an excellent conductor of electricity.
  • It is extremely thin and lightweight.
  • It has high flexibility and strength, making it ideal for advanced devices like flexible screens and super-fast processors.

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