MITIHANI POPOTE EXAMINATIONS SERIES FORM FOUR CHEMISTRY EXAMINATION SERIES 9 (With Marking Guide)

By on 0
FORM FOUR CHEMISTRY EXAMINATION SERIES 9 MITIHANI POPOTE EXAMINATIONS SERIES - FORM FOUR CHEMISTRY SERIES 9

MITIHANI POPOTE EXAMINATIONS SERIES

FORM FOUR CHEMISTRY EXAMINATION SERIES 9

YEAR: 2022

SECTION A (15 Marks)

Answer all questions in this section

1. For each of the items (i) – (x), choose the correct answer from among the given alternatives and write its letter beside the item number in the answer sheet provided.

  1. P and Q are atoms of elements in the same period. P is in group I and Q is in group II which of the following statements is not true about P and Q?
    A. P and Q have the same number of energy levels.
    B. Q has one more proton than P in its nucleus.
    C. P has one more electron than Q in its valency shell.
    D. The atomic number of Q is greater than that of P.
    E. P and Q have equal number of neutrons.
    Answer: E
    Explanation: P (Group I) and Q (Group II) are in the same period, so they have the same number of energy levels (A is true). Q has one more proton (and thus higher atomic number) than P (B and D are true). P has one valence electron, Q has two, so C is false (P has fewer valence electrons). Neutrons depend on isotopes, not necessarily equal (E is not true).
  2. Which of the following pairs of oxides are gaseous at room temperature?
    A. Carbon dioxide and copper (II) oxide
    B. Sulphur dioxide and copper (II) oxide
    C. Copper (II) oxide and lead (II) oxide
    D. Sulphur dioxide and carbon dioxide
    E. Iron (III) oxide and carbon dioxide
    Answer: D
    Explanation: Sulphur dioxide (SO₂) and carbon dioxide (CO₂) are gases at room temperature, while metal oxides like CuO, PbO, and Fe₂O₃ are solids.
  3. In electrolysis, the equivalent of an element is the mass of the element liberated by:
    A. 1 coulomb of electricity
    B. 96,500 coulombs of electricity
    C. 2 coulombs of electricity
    D. 9650 coulombs of electricity
    E. Electrolytic process
    Answer: B
    Explanation: The equivalent weight is the mass liberated by 1 Faraday (96,500 coulombs), as per Faraday’s laws of electrolysis.
  4. What is the name of the alkene shown below?
    CH₃CHCH₂C=CH₂
    C₂H₅
    A. 2-methylpent-4-ene
    B. 2-methylpentene
    C. 4-methylhex-1-ene
    D. 4-ethylpent-1-ene
    E. 4-ethylpent-4-ene
    Answer: D
    Explanation: The structure is CH₃-CH(C₂H₅)-CH₂-C(=CH₂)-H. The longest chain has 5 carbons with a double bond at carbon 1 (pent-1-ene). An ethyl group (C₂H₅) is on carbon 4, making it 4-ethylpent-1-ene.
  5. Which of the following is not true about bases?
    A. Most bases have bitter taste
    B. Bases are slippery when rubbed between fingers
    C. Bases neutralize acids to form salt and water only
    D. Weak base is the one that dissociates completely in solution
    E. Are compounds which have oxide or hydroxide
    Answer: D
    Explanation: Weak bases dissociate partially, not completely, in solution. All other statements about bases are true.
  6. When a burning fuel produces colour it means there is:
    A. Adequate supply of oxygen with production of soot
    B. Inadequate supply of oxygen without production of soot
    C. Inadequate supply of oxygen with production of soot
    D. Inadequate supply of oxygen with production of less heat
    E. Adequate supply of oxygen with production of more heat
    Answer: C
    Explanation: Coloured flames (e.g., yellow) indicate incomplete combustion due to insufficient oxygen, producing soot (carbon particles).
  7. It is possible to collect oxygen by downward displacement of water, because oxygen is:
    A. Denser than water
    B. Soluble in water
    C. Slightly soluble in water
    D. Floats in water
    E. Insoluble in water
    Answer: C
    Explanation: Oxygen is slightly soluble in water, allowing collection by displacing water downward in a gas jar.
  8. If two gas jars labeled A and B contain 22.4 dm³ of oxygen and 22.4 dm³ of nitrogen respectively at STP, then it is true that:
    A. There were 6.02 × 10²³ molecules of oxygen in A and 6.02 × 10²³ molecules of nitrogen in B
    B. There were 6.02 × 10²³ atoms of oxygen in A and 6.02 × 10²³ atoms of nitrogen in B
    C. There were 12.04 × 10²³ molecules of oxygen and nitrogen in their respective jars
    D. 6.02 × 10²³ molecules of oxygen in A and 6.02 × 10²³ molecules of nitrogen in jar A and B respectively
    E. Jars A and B contain 96,500 molecules of oxygen and nitrogen respectively
    Answer: A
    Explanation: At STP, 22.4 dm³ of any gas contains 1 mole (6.02 × 10²³ molecules). Jar A (O₂) and jar B (N₂) each contain 6.02 × 10²³ molecules.
  9. One of the following chemical equations is an example of a precipitation reaction:
    A. AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
    B. NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l)
    C. CaCO₃(s) → CaO(s) + CO₂(g)
    D. Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)
    E. C₂H₆(g) + O₂(g) → 2CO₂(g) + 3H₂O(l)
    Answer: A
    Explanation: Precipitation reactions form an insoluble solid (precipitate). AgCl(s) is insoluble, making this a precipitation reaction.
  10. Which of the following is an agricultural chemical product made by application of chemistry?
    A. Drugs
    B. Pesticides
    C. Clothes
    D. Yeast
    E. Cement
    Answer: B
    Explanation: Pesticides are chemical products used in agriculture to control pests, synthesized through chemical processes.

2. Match the items in LIST A with the correct responses in LIST B, by writing the letter of the correct response beside the item number in the answer sheet provided.

List A List B Answer
The strongest oxidizing agent A. Chlorine
B. Iodine
C. Astatine
D. Fluorine
E. F > Cl > Br > I > As
F. Bromine
G. Oxygen
H. I > Br > Cl > F		 D
The third oxidizing agent F
The weakest oxidizing agent C
The second oxidizing agent A
Decreasing oxidizing power E

Explanation: Oxidizing power of halogens decreases down Group VII: F > Cl > Br > I > As. Fluorine is the strongest, astatine the weakest.

SECTION B (70 Marks)

Answer all questions in this section

3. (a) State whether each change below is a physical change or chemical change:

  1. Glass bottle breaking: Physical – No new substances formed, only shape changes.
  2. Coal burning in air: Chemical – Forms CO₂ and other products, altering composition.
  3. Dissolving sugar in ethanol: Physical – Sugar remains chemically unchanged, only dissolves.
  4. Butter and sugar being made into toffee: Chemical – Heating causes new compounds to form.
  5. Wet hair drying: Physical – Water evaporates, no chemical change in hair.

(b) Coal contains the impurity of sulphur. When sulphur burns in air it forms sulphur dioxide. What volume of this polluting gas is produced at S.T.P when 1.0 g of sulphur burns?

Reaction: S(s) + O₂(g) → SO₂(g). Moles of S = 1.0 / 32 = 0.03125 mol. 1 mol S produces 1 mol SO₂. Volume of SO₂ = 0.03125 × 22.4 = 0.7 dm³.
Answer: 0.7 dm³.

4. (a) Write down the names and formulae of three common acids in the laboratory:

Name Formula
Hydrochloric acid HCl
Sulphuric acid H₂SO₄
Nitric acid HNO₃

(b) Write down the products formed when each of the following pair of compounds reacts:

  1. Acid and metal: Salt and hydrogen gas (e.g., Zn + 2HCl → ZnCl₂ + H₂).
  2. Acid and metal carbonate: Salt, water, and carbon dioxide (e.g., CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂).
  3. Acid and metal hydroxide: Salt and water (e.g., NaOH + HCl → NaCl + H₂O).

(c) Describe a test for identifying the gaseous product in b(i) and b(ii):

  • Hydrogen (b(i)): Produces a “pop” sound when a burning splint is brought near.
  • Carbon dioxide (b(ii)): Turns limewater (Ca(OH)₂) milky due to CaCO₃ formation.

5. (a) Hydrated sodium carbonate (Na₂CO₃·YH₂O) solution was made by dissolving 178 g of its crystals to make a litre of solution. 20 cm³ of the solution was found to neutralize 25 cm³ of a molar solution of nitric acid solution. Show all procedures to find the value of Y in the formula of hydrated carbonate.

Reaction: Na₂CO₃ + 2HNO₃ → 2NaNO₃ + H₂O + CO₂. Moles of HNO₃ = 1 M × 0.025 dm³ = 0.025 mol. Moles of Na₂CO₃ = 0.025 / 2 = 0.0125 mol in 20 cm³. Moles in 1 L = (0.0125 / 0.02) × 1 = 0.625 mol. Molar mass = 178 / 0.625 = 284.8 g/mol. Molar mass of Na₂CO₃ = 106 g/mol. Mass of YH₂O = 284.8 - 106 = 178.8 g. Y × 18 = 178.8, Y ≈ 10.
Answer: Y = 10.

(b) Name the indicator you would choose for the following titration:

  1. Hydrochloric acid versus ammonia solution: Methyl orange – Strong acid vs. weak base, pH changes sharply near 4-5.
  2. Acetic acid versus sodium hydroxide: Phenolphthalein – Weak acid vs. strong base, pH changes near 8-10.

6. (a) Define the following terms:

  1. Empirical formula: Simplest whole-number ratio of atoms in a compound.
  2. Molecular formula: Actual number of atoms in a molecule, a multiple of the empirical formula.

(b) Chemical analysis shows that the empirical formula of the compound is CH₂O and its relative molar mass is 60:

  1. Calculate its molecular formula:
    Empirical mass = 12 + 2×1 + 16 = 30. n = 60 / 30 = 2. Molecular formula = (CH₂O)₂ = C₂H₄O₂.
  2. Name the compound formed and write its open structural formula:
    Name: Ethanoic acid (acetic acid). Structure: CH₃COOH (CH₃-C(=O)-OH).

(c) Write balanced chemical equations of the reaction between the compound named in 6(b)(ii) with:

  1. Ethanol:
    CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O
  2. Sodium hydroxide:
    CH₃COOH + NaOH → CH₃COONa + H₂O

7. (a) In our daily life activities we use different types of fuels for various purposes. What is the energy value of a fuel?

Answer: The energy value is the amount of energy released per unit mass or volume when a fuel undergoes complete combustion.

(b) Name two examples of each of the following types of fuels:

  1. Solid fuel: Coal, wood.
  2. Gaseous fuel: Methane, propane.
  3. Liquid fuel: Petrol, diesel.

(c)

  1. Why is coal not recommended as a domestic fuel?
    Answer: Produces smoke and pollutants (e.g., SO₂), causing health and environmental issues.
  2. List two advantages of liquid fuel over solid fuels:
    • Easier to transport and store (e.g., in tanks).
    • Burns more cleanly, producing less ash.
  3. What are two gaseous fuels used in industries?
    Answer: Natural gas, hydrogen.

8. (a) Distinguish between the following:

  1. Endothermic reaction from exothermic reaction:
    Endothermic: Absorbs heat, ΔH positive. Exothermic: Releases heat, ΔH negative.
  2. Reversible reaction from irreversible reaction:
    Reversible: Can proceed in both directions (e.g., N₂ + 3H₂ ⇌ 2NH₃). Irreversible: Proceeds in one direction (e.g., combustion).

(b) The equation at which ammonia is manufactured is:

N₂(g) + 3H₂(g) ⇌ 2NH₃(g) ΔH = -46.2 kJ/mol
The equilibrium concentration of ammonia increases as the temperature is lowered:

  1. Is heat evolved or absorbed when ammonia is formed?
    Answer: Heat is evolved (exothermic, negative ΔH).
  2. What will be the effect on the equilibrium concentration of ammonia if temperature and pressure are increased?
    Answer: Increased temperature shifts equilibrium left (less NH₃, as reaction is exothermic). Increased pressure shifts right (more NH₃, as 4 moles gas → 2 moles).

(c) List factors which can alter the rate of a chemical reaction (four factors):

  • Temperature
  • Concentration
  • Catalyst
  • Surface area

9. (a) Give the name of the metal which meets the following information:

  1. The metal which must be kept in kerosene to protect it from air and water: Sodium – Highly reactive, oxidizes rapidly.
  2. The metal which is found in limestone: Calcium – Limestone is CaCO₃.
  3. The metal in green colour which gives a black residue on heating or black oxide: Copper – CuCO₃ (green) forms CuO (black).
  4. The metal of which its oxide is yellow when hot and white when cold: Zinc – ZnO behaves this way.

(b) The following chemical substances were found in a school laboratory of Nindi secondary school, which warning sign is likely to be found on each of the following containers:

  1. Mosquito spray: Flammable – Contains volatile organic compounds.
  2. Concentrated sulphuric acid: Corrosive – Causes severe burns.
  3. A bottle of lead nitrate: Toxic – Lead compounds are harmful if ingested or inhaled.

10. (a) Copy and complete the following table. It shows the products of electrolysis of aqueous solutions using carbon (inert) electrodes.

Solution Product at Anode Product at Cathode
Copper (II) sulphate Oxygen (O₂) Copper (Cu)
Sodium chloride Chlorine (Cl₂) Hydrogen (H₂)
Dilute sulphuric acid Oxygen (O₂) Hydrogen (H₂)

(b) What current must be supplied in a refinery to produce one metric ton (1000 kg) of copper electrolytically within 24 hours?

Mass = 1000 kg = 10⁶ g. Moles of Cu = 10⁶ / 63.5 = 15748.03 mol. Cu²⁺ + 2e⁻ → Cu, so electrons = 15748.03 × 2 = 31496.06 mol. Charge = 31496.06 × 96500 = 3.039 × 10⁹ C. Time = 24 × 3600 = 86400 s. Current = 3.039 × 10⁹ / 86400 ≈ 35173.61 A.
Answer: Approximately 35174 A.

(c) Suggest one method of separating the following mixtures:

  1. Green solution from leaves: Chromatography – Separates pigments based on solubility.
  2. Ammonium chloride from sand: Sublimation – NH₄Cl sublimes, leaving sand.
  3. Ethanol and distilled water: Fractional distillation – Ethanol boils at 78°C, water at 100°C.
  4. Cooking oil and drinking water: Separating funnel – Immiscible liquids separate by density.

11. (a) For each of the following plants, which nutrient do you think is missing?

  1. The plant has poor root growth: Phosphorus – Essential for root development.
  2. Plant does not flower, parts of the leaves are dead: Potassium – Promotes flowering and cell health.
  3. The plant has very pale-yellow leaves: Nitrogen – Needed for chlorophyll production.
  4. The plant has yellow leaves and very poor growth: Magnesium – Component of chlorophyll, vital for growth.

(b) Distinguish manure from fertilizer:

Manure: Organic, from animal/plant waste, improves soil structure but has variable nutrient content. Fertilizer: Inorganic, synthetic, provides specific nutrients in precise amounts.

(c) With the aid of a chemical equation, briefly explain how:

  1. Temporary hardness of water can be removed by boiling:
    Ca(HCO₃)₂(aq) → CaCO₃(s) + H₂O(l) + CO₂(g)
    Explanation: Boiling decomposes calcium bicarbonate into insoluble CaCO₃, removing hardness.
  2. Permanent hardness of water can be removed by chemical means:
    CaSO₄(aq) + Na₂CO₃(aq) → CaCO₃(s) + Na₂SO₄(aq)
    Explanation: Sodium carbonate precipitates Ca²⁺ as CaCO₃, removing hardness.

12. (a) Briefly explain four causes that contribute to water pollution:

  • Industrial discharge: Chemicals and heavy metals contaminate water bodies.
  • Agricultural runoff: Fertilizers and pesticides leach into rivers.
  • Sewage: Untreated waste introduces pathogens and nutrients.
  • Oil spills: Hydrocarbons from spills harm aquatic ecosystems.

(b) Give any three points of Dalton’s atomic theory:

  • Elements are made of indivisible atoms.
  • Atoms of the same element are identical in mass and properties.
  • Atoms combine in simple whole-number ratios to form compounds.

SECTION C (15 Marks)

Answer one (1) question from this section

13. (a) Describe the extraction of sodium from its ore and write all the reaction equations:

Description: Sodium is extracted from sodium chloride (NaCl) via electrolysis in the Downs cell. Molten NaCl is mixed with CaCl₂ to lower the melting point. A carbon anode and iron cathode are used. Sodium is produced at the cathode, and chlorine at the anode.

Reactions:

  • Overall:
    2NaCl(l) → 2Na(l) + Cl₂(g)
  • Cathode:
    Na⁺ + e⁻ → Na
  • Anode:
    2Cl⁻ → Cl₂ + 2e⁻

(b) State four uses of sodium metal:

  • Used in sodium-vapour lamps for street lighting.
  • As a coolant in nuclear reactors.
  • In the manufacture of sodium compounds (e.g., NaOH).
  • As a reducing agent in organic synthesis.

No comments

Post a Comment

Subscribe to: Post Comments (Atom)
© all rights reserved
made with by templateszoo