Chemistry Paper 2 Questions and Answers - Wahundura Boys Mock Examination 2023

INSTRUCTIONS:

Answer ALL the questions in the spaces provided in the question paper.
All working MUST be clearly shown where necessary.
This paper consists of 10 printed pages.
Mathematical tables and electronic calculators may be used.

QUESTIONS

The grid below represents part of the periodic table. Study it and answer the questions that follow. The letters do not represent the actual symbols of the element.
1. What name is given to the group of elements to which Q and R belong? (1 mark)
2. Write the formula of the compound formed when Q and P combine. (1 mark)
3. Name the type of bond formed in (b) above. (1 mark)
4. How does the atomic radii of O and P compare? Give a reason. (2 marks)
5. Draw a dot (.) and cross (x) diagram for the compound formed between N and F. (1 mark)
6. Explain how you would obtain a pure sample of the carbonate of K from its mixture with Lead carbonate powder. (2 marks)
7. Give one use of element M. (1 mark)
8. The melting point of M is -189°C lower than that of F -102°C. Explain this difference in their melting points. (2 marks)
The list below shows the formulae of some organic compounds. Use letters T1 to T6 to answer the questions that follow.
T₁ – CH₃CH₂CH₂CH₂CH₃
T₂ – CH₃CH₂CH₂COOC₂H₅
T₃ – CH₃CH₂CH₂CH₂OH
T₄ – CH₃CH₂CH₂COOH
T₅ – CH₃CH₂CHCH₂
T6 – CH₃CCCH₃
1. 1. Select two compounds which are not hydrocarbons (1mk)
  2. Would decolorize both bromine water and acidified potassium manganite (VII) (1mk)
  3. Would produce hydrogen gas when reacted with potassium metal (1mk)
2. Select a compound which would produce bubbles of a gas when reacted with sodium carbonate. (1mk)
3. 1. Identify the compound that is likely to undergo additional polymerization.
    Give a reason for your answer. Using two molecules show how polymerization occurs.
    1. Compound (1mk)
    2. Reasons (1mk)
    3. Polymerization (1mk)
  2. Name the process by which compound T2 is formed and identify the compounds that were used to form it.
    1. Process (1mk)
    2. Compounds (1mk)

What is meant by the term molar enthalpy of combustion? (1mks)
The enthalpies of combustion of carbon, hydrogen and ethanol are given below.
C_(s) + O_{2 (g)} → CO_{2 (g)} ∆ H = -393kJmol^-1
H_{2 (g)} + ½ O_{2 (g) →} H₂O (l) ∆H = - 286 kJmol^-1
Enthalpy of combustion of ethanol ∆H = -1369kJ/ mol
1. Draw an energy cycle diagram that links the enthalpy of formation of ethanol to enthalpies of combustion of Carbon, hydrogen and ethanol (2 marks)
2. Determine the enthalpy of formation of ethanol (2 marks)

An experiment was carried out where different volumes of dilute nitric (v) acid and
Aqueous potassium hydroxide both at 25°C were mixed and stirred with a thermometer.
The highest temperature reached by each mixture was recorded in the table below.

Volume of nitric (V) acid (cm³)	4	8	12	16	20	24	28	32	36
Volume of potassium hydroxide cm³	36	32	28	24	20	16	12	8	4
Highest temperature of mixture	19.8	22.2	24.6	27.0	27.0	25.0	23.0	21.0	19.0

Plot a graph of highest temperature (vertical axis) against volume of nitric(v) acid. (horizontal axis) 3mks
Using your graph, determine the;
1. Highest temperature reached ( 1 marks)
2. The volume of the acid that reacted when the highest temperature is reached. (1marks)
3. The amount of heat liberated during the neutralization process
  (Specific heat capacity is 4.2Jg^-1K^-1 and the density of solution is 1.0gcm^-3 (2 marks)
4. The molar enthalpies of neutralization for dilute hydrochloric acid and dilute nitric (v) acid are -55 kJmol^-1 while that of ethanoic acid is -52.2kJ/mol. Explain this observation. (1mks)

1. The standard electrode potentials for the elements chloride and magnesium are:
  Cl_{2 (aq)} + 2é → 2Cí_(aq) E^θ= +1.36V
  Mg²⁺_(aq) + 2é → Mg_(s) E^θ= –2.36V
  1. Which one for the two elements will act as an oxidizing agent? Explain your choice. (2 marks)
  2. Calculate the electromotive force of a cell where the overall reaction is:
    Cl_2(aq) + Mg_(s) → MgCl_2(aq) (1mark)
2. The table below gives the standard electrode potentials for divalent metals represented by the letters P, Q, R and S (not their symbols of elements). Use it to answer the question that follow.
  Metal E^θ (volts)
  P +1.50
  Q +0.44
  R +0.34
  S –0.76
  1. Which one of the metals cannot be displaced from a solution of its ions by any other metals in the table? Explain. (2 marks)
  2. Metals P and Q were connected to from a cell as shown in the diagram below.
    1. On the diagram label the metals P and Q , the flow of electrons and indicate the ions in solution (2 marks)
    2. Write equations (half equations) of the reactions taking place at the electrodes.
      1. Electrode P (1 mark)
      2. Electrode Q (1 mark)
    3. State two functions of the salt bridge. (2 marks)
    4. What must be observed about the choice of a salt bridge? (1 mark)
  3. A metallic couple of the metal S and Z produced a voltage of +1.71volts.
    (Assume that S has the higher negative electrode potential)
    1. Calculate the standard electrode potential for metal Z. (1 mark)
    2. Arrange the metals P, Q, R and Z in their decreasing order of reactivity. (1 mark)
The flow chart below shows some reactions starting with lead (II) nitrate. Study it and answer the questions that follow.
1. 1. State the conditions necessary in Step 4 (1mk)
  2. Identify
    1. Reagent K (1/2mk)
    2. Gas Q (1/2mk)
    3. Acidic products S and R. (1mk)
  3. Write
    1. The ionic equation for the reaction in step 6. (1mk)
    2. The equation for the reaction in Step 4. (1mk)
2. The use of materials made by Lead in roofing and water pipes is being discouraged. State
  1. Two reasons why these materials have been used in the past. (2mks)
  2. One reason why their use is discouraged. (1mk)
3. The reaction between Lead (II) Nitrate and sulphuric (vi) acid starts and stops immediately. Explain (2mks)
1. A student was supplied with a colourless liquid suspected to be water.
  1. Describe one chemical test that could have been used to show that the liquid was water (2mk)
  2. How could it have been shown that the liquid was pure water? (1mk)
2. The flow chart below shows the various stages of water treatment. Study it and answer the questions that follow
  1. Which substances are likely to be removed in filtration unit I? (1mk)
  2. What is the purpose of process Y (1mk)
  3. What is the purpose of the addition of sodium hypochlorite (1mk)
3. It was confirmed that magnesium sulphate was present in the tap water
  1. What type of hardness was present in the water? (1mk
  2. Explain one method that can be used to remove the water hardness. (2mks)
4. The set-up below was used to collect gas F, produced by the reaction between water and calcium metal.
  1. Name gas F (1mk)
  2. At the end of the experiment, the solution in the beaker was found to be a weak base. Explain why the solution is a weak base. (2 marks)
  3. Give one laboratory use of the solution formed in a beaker. (1 mark)
1. 1. Name the allotropes of sulphur (1mk)
  2. Sulphur is mined using the Frasch process which uses super-heated water at 170°c and hot compressed air.
    1. Explain how water at 170°c is obtained. (1mk)
    2. State one role of the super-heated water (1mk)
    3. State and explain what happens when wet petals of red flowers are put in a gas jar full of sulphur (iv) oxide (2mark
    4. Write an equation for the reaction of sulphur (IV) oxide and concentrated Nitric (V) acid. (1mark)
    5. 1. Name the catalyst used in contact process (1mark)
      2. An equilibrium exists as
        2SO_2(g) + O_2(g) 2SO_3(g)
        State and explain what happens if
        
        More oxygen is added to the system (2 marks)
        
        Pressure is decreased (2 marks)

MARKING SCHEME

1. Alkaline earth metals (1mk)
2. Q²P² → QP – NB: metal should be followed by a non-metal and not vice versa. (1mk)
3. Ionic bond. (1mk)
4. The atomic radius of P is smaller than that of O. P has higher/stronger nuclear
  force of attraction than O. P has more number of protons than O.
  NB: Comparative words MUST be used. (2mk)
5. NB: outermost electrons in the atoms of F must be shown (1mk)
6. Add water to the mixture of K carbonate and lead carbonate and stir. K carbonate
  dissolves while lead carbonate does not.
  Filter to obtain K carbonate solution as a filtrate and lead carbonate as the residue.
  Evaporate the filtrate to obtain crystals of carbonate of K
  Wash the residue with distilled water and dry between filter papers. (2mks)
7. Used in light bulbs to provide an inert environment to prevent oxidation.
  NB: reject used to make light bulbs.
  Used as an insulator in arch – welding. (1mk)
8. M is a monoatomic gas while F is a diatomic gas; the Van der waal forces in M are weaker than in F hence the low m.p.t (2mks)
1. 1. T₂ , T₃ , T₄ any two (1mk)
  2. T₅ and T₆ (1mk
  3. T₃ and T₄ (1mk)
2. T₄ (1mk)
3. 1. T₅ or T₆ (1mk)
  2. Reason: it is unsaturated (1mk)
  3. Polymerization (1mk)
  4. 1. Process: Esterification
    2. Compounds (1mk)
      1. Butanoic acid (CH3CH2CH2COOH)
      2. Ethanol (C2H5OH)
1. The amount of heat liberated when one mole of a substance is burnt completely in excess oxygen.
  rej- heated in oxygen
  rej- heated required to burn ….
  NB: burning must be complete
2. 1. Correct energy cycle with arrows pointing right 1mk
    Balancing all the equations – 1mark
    NB: If an energy level diagram (axis labelled) is drawn with correct arrows award. (1marks
  2. ∆H₁ = ∆H₂ + ∆H₃2(-393) + 3(-286) = ∆H₂ + - 1369
    ∆H_f =∆H₂ = -786 + - 858 + 1369 kJmol^-1 (J) must be capital
    = -275 kJ/Mol (2mks)
    Penalize ( ½ marks) if units missing.
    Penalize ( ½ mark if –ve sign is missing.
3. 1. NB: Straight lines ½ mk each with extrapolation
    Plotting 1mk
    Axis label ½ mk each
    1. x^oC – must be read from the extrapolated value from the graph. (1 mk)
    2. Vcm³ – must be read from the graph correctly. ( 1 mk)\
    3. ∆H = MC∆T
      
      NB: final answer must have –ve sign otherwise penalise (½ mk) (1mk)
    4. Ethanoic acid is a weak acid therefore heat is used to ionize it before neutralization occurs.
1. 1. Cl₂1 mk It has a positive standard electrode potential hence a higher tendency to gain electrons 1mk
  2. Cl_2(aq) + 2é→ 2Cl^-_(aq) E^θ = +1.36V
    Mg_(s) → Mg²⁺ _(aq)+ 2é E^θ = +2.36V
    E^θ = +3.72
    E^θ = +3.72V
2. 1. Metal S: 1mk it has the highest negative e.m.f hence a high oxidizing power therefore low tendency to gain electrons and be displaced1 mk
  2. 2. P: P²⁺_(aq)+ 2é → P(s)
      Q: Q_(s)→ Q²⁺ _(aq)+ 2é
    3. It completes the circuit 1 mk
      It ensures electrical neutrality and balance of ions between the two cells 1 mk
    4. The salt in the bridge should not react with ions in the solution
  3. 1. E^θ cell = E^θ reduction - E^θ oxidation
      +1.71 = Z – – 079
      Z = +1.71 – 0.76
      = + 0.95V
    2. Q, R, Z, P (1 marks)
1. 1. Heat
  2. 1. K₂CO₃ //Na₂CO₃ // (NH₄)₂ CO₃ // Names 1/2
    2. Oxygen 1/2
  3. 1. Pb²⁺ _(aq) + CO^₂-_{3 (aq) →} PbCO_{3 (s)}(1mk)
      PbO_(s) + H₂ (g) → Pb _(s) + H₂O _(l)
2. 1. Cheap / corrosion resistant /durable any two
  2. Lead is poisonous / harmful
3. The reaction produces insoluble lead (II) sulphate which coats the surface if Lead (II) Nitrate preventing further reaction.
1. 1. When blue anhydrous cobalt (II) chloride paper is dipped in a sample of the liquid, it turns to pink√.
    White anhydrous copper (II) sulphate turns to blue√ when sample of the liquid is added.
  2. When the liquid is heated to boil, its boiling point is 100°C at sea level/one atmosphere pressure√.
    When the liquid is cooled to solidify, its freezing point is 0°C at sea level/one atmosphere pressure√.
    When the density of liquid is determined it is 1gcm^-3 at 4°C √
2. 1. Large solid particles like rock/sang√
  2. Causes small suspended particles to settle√.
  3. To kill germs/microorganisms√
3. 1. Permanent hardness√
  2. Addition of sodium carbonate√ that precipitates Ca²⁺ and Mg²⁺ ions
    Distillation√ to remain with MgSO₄ / CaSO₄ as residue√.
    Use ion-exchange permutit√ which will remove Ca²⁺ and Mg²⁺ ions√.
4. 1. Hydrogen/H₂√
  2. Calcium hydroxide is slightly soluble√ in water. It is partially dissociated into few Ca²⁺ and OH^-(aq) ions. √
  3. Test for the presence of CO2 gas√
    Preparation of ammonia gas.
1. 1. Name the allotropies of sulphur (1mk
    Rhombic sulphur√½
    Monoclinic sulphur √½
  2. Sulphur is mined using the Frasch process which uses super-heated water at 1700c and hot compressed air.
    Explain how water at 1700c is obtained. (1mk)
    Heating water at 10 atmosphere pressure √1mk
    OR
    Heating water at high pressure.√1mk
    State one role of the super-heated water (1mk)
    To melt the sulphur deposits√1mk
  3. State and explain what happens when wet petals of red flowers are put in a gas jar full of sulphur (IV) oxide (2marks)
    The red petals turn white√1mk
    Sulphur (IV) oxides bleaches the flower petals √1mk
  4. Write an equation for the reaction of sulphur(IV) oxide and concentrated Nitric (V) acid (1mark)
  5. 1. Name the catalyst used in contact process (1mark)
      Vanadium (V) oxide √1mk
      OR
      Platinum√1mk
    2. An equilibrium exists as
      2SO_2(g) + O_2(g) 2SO_3(g)
      1. Because adding more oxygen increase the concentration of reactants in the forward reaction√1mk
      2. Equilibrium moves to the left 1mk decrease in pressure leads to increase in volume/no of molecules therefore equilibrium moves to the side with decreased number if molecules