Chemistry Paper 2 Questions and Answers - Form 4 End Term 2 2021

CHEMISTRY
PAPER 2
TIME: 2 HOURS

INSTRUCTIONS

Answer all the questions
KNEC mathematical tables and silent electronic calculators may be used
All workings must be clearly shown where necessary
Candidates should answer all questions in ENGLISH

A student set-up the following apparatus to prepare carbon (II) oxide from charcoal in the laboratory.
1. State the purpose of potassium hydroxide solution (1mk)
2. Identify gas B (1mk)
3. Name two substances that react together to produce gas B (2mks)
4. Write balanced equations for reactions in
  1. Combustion tube (1mk)
  2. Flask L (1mk)
5. Describe two simple test that you would use to distinguish between Carbon (IV) oxide and Carbon (II) oxide. (2mks)
6. In another experiment, the student reacted charcoal with excess hot concentrated nitric (v) acid.
  1. State one observation made (1mk)
  2. Write balanced equation for the reaction (1mk)
7. State two use of Carbon (II) oxide (1mk)
Use the information in the table below to answer the questions that follow. The letters are not the actual symbols of the elements.

Element Atomic Number M.P(ºC)

A 11 97.8

B 13 660

C 14 1410

D 17 -95

E 20 839
1. Write the electronic arrangement for the ions formed by elements D and A (2mks)
2. Select an element which is :
  1. A poor conductor of electric current (1mk)
  2. The strongest reducing agent (1mk
  3. Has a giant covalent structure (1mk)
  4. In which state will element B exists at 6610c Explain. (1mk)
3. Compare the electrical conductivity of element A and B. Give a reason (1mk)
4. Using dots (.) and crosses (x) to represent the outermost electrons, show the bonding in the compound formed between elements C and D. (2mks)
5. Explain the difference in melting points in elements B and A (2mks)
6. Write an equation for the reaction that takes place between element E and steam. (1mk)
7. Describe how a solid mixture of the Chloride of E and lead (II) Sulphate can be separated into solid sample. (2mks)
Study the flow chart below and answer the questions that follow.
1. Name substance J and draw its structural formula: (2mks)
  Name
  Structural formula
2. What reagents and conditions are necessary for:
  1. Step (III) :
    - Reagent (1mk)
    - Condition
  2. Step II:
    - Reagent (1mk)
    - Condition
3. Name the following
  1. L (1mk)
  2. Gas P (1mk)
  3. Q (1mk)
  4. M (1mk)
4. Write the equation of the reaction that occur in step (IV) (1mk)
5. Give the name of process in step (V) (1mk)
6. If the relative Molecular Mass of R is 21,000, determine the value of n. (C = 12.0, H = 1.0) (2mks)
1. Define an electrolyte (1mk)
2. Explain why the following substances conduct an electric current (2mks)
  1. Magnesium metal
  2. Molten magnesium Chloride
3. Study the reaction scheme below and answer the questions that follow.
  1. Write the formula of P and Q (2mks
  2. Write an ionic equation for the formation of P (1mk)
  3. Name process (i) (1mk)
  4. Write a balanced equation for the formation of white precipitate K (1mk
  5. State the condition required for process (III) (1mk)
  6. Which physical property is exhibited in process (III) (1mk
  7. State one use of magnesium hydroxide (2mks)
    Give one reason
1. At 250c, 50g of potassium nitrate were added to 100g of water to make a saturated solution. What is meant by a saturated solution? (1mk)
2. The table below gives the solubilities of potassium nitrate at different temperatures.
  
  Temperature (ºC) 12 20 28 36 44 52
  
  Solubility g/100g of water 22 31 42 55 70 90
  1. Plot a graph of the solubility of potassium nitrate (vertical axis) against temperature (3mks)
  2. Using the graph
    1. Determine the solubility of potassium nitrate at 150c. (1mk)
    2. Determine the mass of potassium nitrate that remained undissolved given that 80g of potassium nitrate were added to 100cm³ of water and water to 40ºc. (2mks
3. Determine the molar Concentration of potassium nitrate at 15ºc.
  (Assume there is no change in density of water at this temperature)
  (K = 39.0, N = 14.0, O = 16.0) (3mks)
1. Aluminium oxide reacts with both acids and bases
  1. Write an equation for the reaction between aluminium oxide and hydrochloric acid (1mk)
  2. Using the equation in (a) above, calculate the number of moles of hydrochloric acid that would react completely with 153.0g of aluminium oxide (Al = 27.0, O = 16.0) (3mks)
2. Sodium hydroxide pellet were accidentally mixed with sodium chloride, 8.8g of the mixture were dissolved in water to make one litre of solution. 50cm3 of the solution was neutralized by 20.0cm3 of 0.25M Sulphuric (vi) acid
  1. Write the equation for the reaction that took place. (1mk)
  2. Calculate the:
    1. Number of moles of the substance that reacted with Sulphuric (vi) acid (2mks
    2. Number of moles of the substance that would react with Sulphuric (vi) acid in the one litre solution. (1mk)
    3. The percentage of sodium chloride in the mixture. (2mks)
The flow chart below illustrates the industrial extraction of lead metal.
Study it and answer the questions that follow.
1. 1. Name the ore that is commonly used in the process (1mk
  2. Explain what takes place in the roasting furnace (1mk)
  3. Identify gas P (1mk)
  4. Write the equation for the main reaction that takes place in the smelting furnace. (1mk)
  5. What is the purpose of adding iron in the smelting furnace? (1mk)
  6. Give two environmental hazards likely to be associated with extraction of lead. (2mks)
2. Explain why hard water flowing in lead pipes may be safer for drinking than soft water flowing in the same. (2mks)
3. State one use of lead other than the making of lead pipes (1mk)

MARKING SCHEME

A student set-up the following apparatus to prepare carbon (II) oxide from charcoal in the laboratory.
1. State the purpose of potassium hydroxide solution (1mk)
  - To absorb excess Carbon (IV) oxide or gas B
  - To absorb unreacted Carbon (IV) oxide
2. Identify gas B (1mk)
  - Carbon (IV) oxide / CO2
3. Name two substances that react together to produce gas B (2mks)
  - Any Carbonate/hydrogen Carbonate and acid
4. Write balanced equations for reactions in
  1. Combustion tube (1mk)
    - CO_2(g) + C_(s)→ 2CO_(g)
  2. Flask L (1mk)
    - KOH_(aq) + CO_2(g) → KHCO_3(aq)
5. Describe two simple test that you would use to distinguish between Carbon (IV) oxide and Carbon (II) oxide. (2mks)
  - CO does not form white precipitate with Ca(OH)₂ while CO2 does
  - CO burns with a blue flame while CO2 does not support combustion.
6. In another experiment, the student reacted charcoal with excess hot concentrated nitric (v) acid.
  1. State one observation made (1mk)
    - Brown fumes produced
    - Black substance dissolves
  2. Write balanced equation for the reaction (1mk)
    HNO_3(aq) + C_(s) → CO_2(g) + 4NO_2(g)
7. State two use of Carbon (II) oxide (1mk)
  - Reducing agent in the extraction of metals from the ore
  - Used as fuels any one correct
  - Manufacture of hydrocarbons
Use the information in the table below to answer the questions that follow. The letters are not the actual symbols of the elements.

Element Atomic Number M.P(ºC)

A 11 97.8

B 13 660

C 14 1410

D 17 -95

E 20 839
1. Write the electronic arrangement for the ions formed by elements D and A (2mks)
  - 2.8.8,
  - 2.8
2. Select an element which is :
  1. A poor conductor of electric current (1mk)
    - D
  2. The strongest reducing agent (1mk)
    - A
  3. Has a giant covalent structure (1mk)
    - C
  4. In which state will element B exists at 6610c Explain. (1mk)
    - Liquid - The melting point is below 6610c
3. Compare the electrical conductivity of element A and B. Give a reason (1mk)
  - B is a better electric conductor than A, because it has more delocalized electrons than A.
4. Using dots (.) and crosses (x) to represent the outermost electrons, show the bonding in the compound formed between elements C and D. (2mks)
5. Explain the difference in melting points in elements B and A (2mks)
  - B has a higher melting point than A because B has more delocalized electrons than A.
  - Therefore B has stronger metallic bond than A thus high melting point.
6. Write an equation for the reaction that takes place between element E and steam. (1mk)
  - E_(s) + H₂O_(g) → EO_(s) + H_2(g)
7. Describe how a solid mixture of the Chloride of E and lead (II) Sulphate can be separated into solid sample. (2mks)
  - Add water to the mixture, Stir, E Chloride dissolves while Lead (II) Sulphate does not. Filter and wash the residue with distilled water.
  - Evaporate the filtrate to obtain solid E Chloride
Study the flow chart below and answer the questions that follow.
1. Name substance J and draw its structural formula: (2mks)
  Name
  - Propane
2. Structural formula
3. What reagents and conditions are necessary for:
  1. Step (III) :
    - Reagent (1mk)- Conc Sulphuric (VI) acid/Conc H2SO4
    - Condition - 160 – 1800c
  2. Step II:
    - Reagent (1mk) - Chlorine gas / C/ (g)
    - Condition - Ur light / sunlight
4. Name the following
  1. L (1mk) - Carbon (IV) oxide
  2. Gas P (1mk) - Hydrogen gas
  3. Q (1mk) - Propan-1-oic acid
  4. M (1mk) - 1-Bromopropane / 2 – Bromopropane
5. Write the equation of the reaction that occur in step (IV) (1mk)
  - 2C₃H₇OH_(l) + 9O_2(g)→ 6CO_2(g) + 8H₂O_(l)
6. Give the name of process in step (V) (1mk)
  - Addition polymerization / polymerization
7. If the relative Molecular Mass of R is 21,000, determine the value of n. (C = 12.0, H = 1.0) (2mks)
  - (3 x 12) + (1 x 6) = 42
    42n = 21,000
    N = ^21,000/₄₂= 500 units
1. Define an electrolyte (1mk)
  - Are substances which when molten or dissolved in water conduct an electric current and decomposes.
2. Explain why the following substances conduct an electric current (2mks)
  1. Magnesium metal - Magnesium metal conducts since it contains free ions
  2. Molten magnesium Chloride
3. Study the reaction scheme below and answer the questions that follow.
  1. Write the formula of P and Q (2mks
    - P – PbSO₄
    - Q – Mg (NO₃)₂
  2. Write an ionic equation for the formation of P (1mk)
    - Pb²⁺_(aq) + SO4^2-_(aq) → PbSO_4(s)
  3. Name process (i) (1mk)
    - Precipitation / Double decomposition
  4. Write a balanced equation for the formation of white precipitate K (1mk)
    - Pb(NO₃)_(aq) + 2HCl_(aq) → PbCl_2(s) + 2HNO_3(aq)
  5. State the condition required for process (III) (1mk)
    - Heat/warm
  6. Which physical property is exhibited in process (III) (1mk)
    - Effect of temperature on solubility
    - It is used as anti-acid medicine because Mg(OH)₂ is a non-toxic base.
  7. State one use of magnesium hydroxide (2mks)
    - Give one reason
1. At 250c, 50g of potassium nitrate were added to 100g of water to make a saturated solution. What is meant by a saturated solution? (1mk)
  - A solution which cannot dissolve any more solute at a particular temperature.
2. The table below gives the solubilities of potassium nitrate at different temperatures.
  
  Temperature (ºC) 12 20 28 36 44 52
  
  Solubility g/100g of water 22 31 42 55 70 90
  1. Plot a graph of the solubility of potassium nitrate (vertical axis) against temperature (3mks)
  2. Using the graph
    1. Determine the solubility of potassium nitrate at 150c. (1mk)
      - 25g per 100g of water
    2. Determine the mass of potassium nitrate that remained undissolved given that 80g of potassium nitrate were added to 100cm³ of water and water to 40ºc. (2mks)
      - Mass dissolved = 62g
        Mass of undissolved = 80 – 62 = 18g
3. Determine the molar Concentration of potassium nitrate at 15ºc.
  (Assume there is no change in density of water at this temperature)
  (K = 39.0, N = 14.0, O = 16.0) (3mks)
  - R.F.M of KNO₃ =101
    Moles of KNO₃in 100g water = 25 = 0.2475 moles
    101
    Moles in 1000g of water = 0.2475 x 1000
    100
    = 2.475 moles
1. Aluminium oxide reacts with both acids and bases
  1. Write an equation for the reaction between aluminium oxide and hydrochloric acid (1mk)
    - Al₂O_3(s) + 6HCl_(aq) → 2AlCl_3(aq) + 3H₂O_(l)
  2. Using the equation in (a) above, calculate the number of moles of hydrochloric acid that would react completely with 153.0g of aluminium oxide (Al = 27.0, O = 16.0) (3mks)
    - R.F.M of Al2O₃
      (27 x 2) + (16 x 3) = 102
      Moles of Al₂O₃ = 153 = 1.5 moles
      102
2. Sodium hydroxide pellet were accidentally mixed with sodium chloride, 8.8g of the mixture were dissolved in water to make one litre of solution. 50cm3 of the solution was neutralized by 20.0cm3 of 0.25M Sulphuric (vi) acid
  1. Write the equation for the reaction that took place. (1mk)
    2NaOH_(aq) + H₂SO_4(aq) → Na₂SO_4(aq) + 2H₂O_(l)
  2. Calculate the:
    1. Number of moles of the substance that reacted with Sulphuric (vi) acid (2mks
      - Mole ratio of NaOH: H2SO4 = 2: 1
        Moles of H₂SO₄ reacted = 20 x 0.25 = 0.005 moles
        1000
        Moles of NaOH reacted = 2 X 0.005 = 0.01moles
    2. Number of moles of the substance that would react with Sulphuric (vi) acid in the one litre solution. (1mk)
      - If 50cm³ of NaOH = 0.01 moles
        1000cm³ of NaOH = 1000 X 0.01
        50
        = 0.2 moles
    3. The percentage of sodium chloride in the mixture. (2mks)
      - Molar mass of NaOH = 40 gmol^-1
        Mass of NaOH reacted = 40 x 0.2 = 8g
        Mass of NaCl = 8.8 – 8.0 = 0.8g
        % of NaCI = 0.8 x 100 = 9.090%
        8.8
The flow chart below illustrates the industrial extraction of lead metal.
Study it and answer the questions that follow.
1. 1. Name the ore that is commonly used in the process (1mk)
    - Galena
  2. Explain what takes place in the roasting furnace (1mk)
    - Some of the Sulphide is converted into Lead Oxide and Sulphur (IV) oxide
  3. Identify gas P (1mk)
    - Carbon (II) oxide or carbon (IV) oxide
  4. Write the equation for the main reaction that takes place in the smelting furnace. (1mk)
    - PbO_(l) + C_(s) → Pb_(l) + CO_(g)
  5. What is the purpose of adding iron in the smelting furnace? (1mk)
    - To reduce unreacted Pbs to Pb
  6. Give two environmental hazards likely to be associated with extraction of lead. (2mks)
    - Sulphur (IV) oxide – causes acid rain
      Lead – causes lead poisoning
2. Explain why hard water flowing in lead pipes may be safer for drinking than soft water flowing in the same. (2mks)
  - Hard water contains Mg²⁺ / Ca²⁺ ions. These ions form a protective layer of calcium Sulphate or Magnesium Carbonate hence does not dissolve lead.
    Soft water does not form these deposits.
3. State one use of lead other than the making of lead pipes (1mk)
  - Radioactive shielding
  - Lead acid accumulators
  - Making roof