Chemistry Paper 2 Questions and Answers - Bunamfan Post Mock 2021 Exams

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INSTRUCTIONS TO CANDIDATES

Answer all the questions in the spaces provided
Mathematical tables and silent electronic calculators may be used
All working must be clearly shown where necessary
This paper consists of 13 printed pages

FOR EXAMINERS USE ONLY

Questions	Maximum Score	Candidate's Score
1	11
2	14
3	12
4	11
5	12
6	10
7	10
TOTAL	80

QUESTIONS

The diagram below shows an experiment to demonstrate the properties of hydrogen as a reducing agent Study it and answer the questions that follow
1. Before lighting hydrogen gas at the jet, it is important to drive off all the air in the combustion tube Explain (1 mark)
2. State what would be observed in the boat containing lead (II) oxide at the end of the experiment (1 mark)
3. Write chemical equations for the reaction taking place;
  1. In the combustion tube (1 mark)
  2. At the jet as the flame burns (1 mark)
4. Why should the supply of hydrogen continue until the apparatus are cool? (1 mark)
5. Why is it important to clamp the glass tube or combustion tube in a slanting position? (1 mark)
6. 1. Cars in Mombasa rust faster than in Kisumu Explain (1 mark)
  2. Give the factors that are necessary for rusting (1 mark)
  3. Name two methods used to prevent rusting (1 mark)
  4. Explain why a nail paced in a sealed tube containing tap water rusts while a nail placed in a sealed tube containing boiled water fails to rust (1 mark)
  5. State two industrial uses of oxygen gas (1 mark)
The grid shown below represents part of the periodic table Study it and answer the question that follow The letters do not represent the actual symbol of the elements
1. What type of bonds would be formed between C and G Explain (2 marks)
2. Write the formulae of the compounds that would be formed between:
  1. D and G (1 mark)
  2. E and G (1 mark)
3. State and explain how the compounds formed in (b) above compare in their melting points in terms of structure and bonding (2 marks)
4. Give the formulae of the oxides of the elements D and F and state the nature of each oxide
  1. D oxide (2 marks)
    Formulae
    Nature
  2. F oxide (2 marks)
    Formulae
    Nature
5. Which of the elements shown does not form an oxide? Explain (1 mark)
6. Which two elements shown on the grid are good conductors of electricity? Explain (2 marks)
7. What name if given to the group of elements represented by letter Y in the periodic table? (1 mark)
1. Brine usually contains soluble calcium and magnesium salts Explain how sodium carbonate is used to purify brine (2 marks)
  The diagram below represents a diaphragm cell used to electrolysed pure brine
  1. Write the equations for the reactions that take place at :-
    1. Cathode (1 mark)
    2. Anode (1 mark)
  2. Name:
    1. Product at U (1 mark)
    2. Another material that can be used instead of titanium (1 mark)
    3. The impurity present in the product at U (1 mark)
    4. State two functions of the diaphragm (2 marks)
  3. Give one industrial use of the product at U (1 mark)
  4. State two environmental hazards associated with extraction of sodium metal (2 marks)
The diagram below illustrates the contact process for the manufacture of sulphuric (VI) acid

Study it and answer the questions that follow
1. Name three possible identities of solid A (1½ marks)
2. 1. Name two impurities removed by the purifier (1 mark)
  2. Why is it necessary to remove the impurities? (1 mark)
3. Write down the equation for the reaction that takes place in the catalytic converter (1 mark)
4. 1. Name two catalysts that can be used in the converter (2 marks)
  2. Which of the two catalysts is most commonly used and why? (1 mark)
5. Why is sulphur (VI) oxide not absorbed directly into water? (1 mark)
6. Give the equation for the reaction that takes place in the absorption chamber (1 mark)
7. Name the main pollutant in the contact process (½ mark)
8. Name one method by which the pollution is controlled in the contact process (1 mark)
Study the table below and answer the questions that follow;
Reduction Half-reaction Eq(Volts)
Ag⁺(aq) + e^- ® Ag(s) + 080
Cu²⁺(aq) + 2e^- ® Cu(s) + 034
2H⁺(aq) + 2e^- ® H2(g) 000
Zn²⁺(aq) + 2e^- ® Zn(s) -076
Na⁺(aq) + e^- ® Na(s) -271
1. Which is the strongest reducing agent in the above half equations? Explain (2 marks)
2. Calculate the electromotive force of a cell consisting of Zinc and silver electrodes immersed in solutions of their respective ions (2 marks)
3. Give the cell representation of the cell in (b) above (1 mark)
4. The diagram below represents an experiment set up used for the electrolysis of aqueous copper (II) sulphate solution Study it and answer the questions that follow;
  1. Name electrodes X and Y (2 marks)
  2. Name gas W (1 mark)
  3. Write the overall equation of the reactions taking place at electrodes X and Y (1 mark)
  4. If a current of 04A was passed through the cell for 15 minutes, calculate the mass of copper that would be liberated (Relative atomic mass of copper = 64, 1F = 96,500C) (3 marks)
The scheme below shows a series of reactions starting with ethanol Study it and answer the questions that follow
1. Give the type of reaction, the reagent(s) and the condition(s) necessary for step 1 to take place (1 mark)
2. Write the equation for the reaction that takes place in step L (1 mark)
3. Name product V and give the equation responsible for its formation (2 marks)
4. Give the reagent(s) and condition(s) necessary for step W to take place (1 mark)
5. Give the IUPAC name and structural formula of compound X (1 mark)
6. Name compound K and state the type of reaction involved in its formation (2 marks)
7. If the relative molecular mass of K is 44800, determine the value of n (C = 12, H = 1) (2 marks)
The set up below is used to measure the change in mass during the course of the reaction between dilute hydrochloric acid (excess) and marble chips at 22°C

Changes in mass were noted at one minute intervals and were as follows
1. Give an equation for the reaction taking place in the flask (1 mark)
2. Why did the mass of the flask change with time? (1 mark)
3. What is the role of cotton wool at the mouth of the flask? (1 mark)
4. Plot a graph of loss in mass (Y-axis) against time (X-axis) Label the curve 22°C (3 marks)
  
  Time (min)
  
  1
  
  2
  
  3
  
  4
  
  5
  
  6
  
  7
  
  Loss in mass(g)
  
  0.26
  
  0.46
  
  0.60
  
  0.69
  
  0.73
  
  0.73
  
  0.73
5. On the graph same axis as in (d) above, sketch the graph you would expect to obtain if the experiment was repeated at 35°C Label the curve 35°C (2 marks)
6. State what would happen if the marble chips were replaced with the same mass of marble powder Explain (2 marks)
7. Why is it not advisable to use sulphuric (VI) acid in place of hydrochloric acid in this experiment? (1 mark)

MARKING SCHEME

1. This is to avoid an explosion because a mixture of hydrogen and air is highly explosive1
2. Grey solid observed 1
3. 1. PbO(s) + H₂(g) → Pb(s) + H₂O(l)1
  2. 2H₂(g) + O₂(g) → 2H₂O(l)/(g)1
4. To prevent re-oxidation of the hot metallic lead by atmospheric oxygen1
5. To prevent water formed in the reaction form running back into the hot part of the glass tube that can cause it to crack1
6. 1. Mombasa is around the Indian Ocean whose water is salty while Kisumu is around lake Victoria whose water is fresh½
    Salt accelerates rusting hence cars in Mombasa will rust faster than in Kisumu½
  2. Water ½ and oxygen ½
  3. Oiling, greasing, painting, galvanizing, electroplating, sacrificial protection, use of silica gel.(any two for 1mk)
  4. Tube of tap water contains dissolved oxygen while tube of boiled water has no oxygen. 1
  5. - A mixture of oxygen and acetylene burns with hot flame used in welding and cutting of metals
    - Oxygen mixed with hydrogen is used in rocket fuel
    - Oxygen is used in steel making where it oxidizes impurities in molten iron.
    - Oxygen is used in hospitals for patients with breathing problems
    - Oxygen is used by high mountain climbers and deep sea divers. any two for 1mk
1. Covalent1 Both elements are non-metals1
2. 1. DG₂1
  2. EG₃1
3. DG₂ has higher melting point than EG3 1
  DG₂ has giant ionic structure with strong ionic bonding1
  EG₃ has a molecular stricture with weak van der waals forces1
4. 1. DO1 Basic oxide1
  2. FO₂1 acidic .oxide1
    
    e) A½ It is a noble gas with the outermost energy level fully occupied by electrons½
    f) D and E1 they contain delocalised electrons1
    g) Transition elements/Transition metals1
1. add aqueous sodium carbonate 1 to precipitate ½ calcium carbonate and magnesium carbonate and filter. ½
  1. Cathode
    - 2H⁺(aq) + 2e → H₂(g) (1 mark)
  2. Anode
    - 2Cl^-(aq) → Cl₂(g) +2e^-(1 mark
2. Name:
  1. Product at U
    - Sodium Hydroxide/ NaOH 1
  2. Another material that can be used instead of titanium (mark)
    - Graphite/platinum 1 reject carbon
  3. The impurity present in the product at U (1mark)
    - sodium chloride/ Nacl 1
  4. State two functions of the diagram (2marks)
    - To prevent mixing of chlorine gas with sodium hydroxide. To allow free movement of ions. 1
    - It prevents the mixing of chlorine gas and hydrogen gas. 1
3. Give one industrial use of the product at U. (1 mark)
  - Manufacture of soap/detergents 1
  - Used to make bleaching agents
  - Used to make bleaching agents
  - Used in purification of bauxite
  - In paper industry
    (Accept any one correct)
4. - Chlorine gas produced is very poisonous and it affects the respiratory system of animals
  - Causes acid rain that causes corrosion of buildings / yellowing of plants etc.
1. Sulphur, iron (II) sulphide, zinc (II) sulphide, lead (II) sulphide, copper (i) sulphide
  any 3
2. 1. Dust ½, arsenic compounds /arsenic oxide½
  2. To avoid poisoning of the catalyst 1
3. 2SO₂(g) + O₂(g) → 2SO₃(g)1
4. 1. - Vanadium (V) oxide 1
    - Platinum /platinised asbestos 1
  2. - Vanadium (V) oxide½
    - It is cheaper and not easily poisoned ½
5. The reaction is highly exothermic causing the solution to boil forming mist1 of sulphuric (VI) acid spray which is corrosive
6. Sulphur (IV) oxide ½
7. - Recycling the unreacted gases 1
  - Reacting the unreacted gases with oxides or carbonates of metals or with heated carbon
    any one
1. Na(s)/Sodium metal 1
  - It has the highest negative reduction potential 1 /(Eº)
2. +0.80 - (-0.76)½ = + 0.80 + 0.76 = + 1.56V1
3. Zn(s) /Zn2+(aq) //Ag+(aq) /Ag(s)1
4. 1. X - Cathode1 Y - anode1
  2. Oxygen1
  3. 4OH-(aq) + 2Cu²⁺(aq) → 2Cu(g) + 2H₂O(l) + O₂(g)1
  4. Q = It Q = 0.4 x (15 x 60) ½
    = 360C½
    Cu²⁺(aq) + 2e^- → Cu(s)½
    2 x 96500 = 64g
    360 = ?
    360 x 64½ = 0.1194g1
    19300
1. Type of reaction: Dehydration½
  Reagent : Concentrated Sulphuric (VI) acid ½
  Condition: 170ºC - 180ºC (single value in that range) ½
2. Mg(s) + 2CH₃COOH(aq) → (CH₃COOH)₂Mg(aq) + H₂(g)1
3. V - Butylethanoate1
  - CH₃COOH(aq) + CH₃CH₂CH₂CH₂OH(l) → CH₃COOCH₂CH₂CH₂CH₃(aq) + H₂O(l)1
4. Reagent: Soda lime½
  - Condition: Heat½
5. Name: Tetrachloromethane/ carbon tetrachloride ½
  - Structure:½
6. Name: Polyethene/polythene½
  - Type of reaction: Addition reaction/Addition polymerization1
7. Molecular mass of -CH2 - CH2 -
  - = 14 + 14
    = 28½
    n = 44800½ = 1600
1. CaCO₃(s) + 2HCl(aq) → CaCl₂(aq) + H₂O(l) + CO₂(g)1
2. The carbon (IV) oxide formed escaped into the atmosphere1
3. To prevent acid from spraying out1
4. In the graph paper (3mks)
5. 1mk for curve 35°C
6. - The reaction rate would increase½
  - Marble powder offers a larger surface area than chips, which causes the rate of reaction to increase1
7. There would be formation of insoluble calcium sulphate that would coat calcium carbonate (Marble chips) stopping the reaction1