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Chemistry Paper 2 Questions and Answers - Lanjet Joint Mock Exams 2023

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INSTRUCTION TO CANDIDATES

  • Answer all the questions in the spaces provided
  • All working must be clearly shown where necessary.
  1.  
    1. 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 elements.
                                                 ChemMocksQ7
      1. Which element will require the least amount of energy to remove one of the outermost electrons? (1mk)
      2. Select the most reactive non- metal. (1mk)
      3. Which of the elements has the greatest tendency of forming covalent? Explain (2mks)
      4. What name is given to the family of elements to which elements O, T and V belong?(1mk)
      5. An element W has atomic number 15. Indicate the position of W on the grid.  (1mk)
      6. Explain why the atomic radius of S is smaller than that of R.  (1mks)
      7. Explain why the atomic radius of Z is smaller than its ionic radius. (1mk)
    2. Study the information given in the table below and answer question that follow.
       Formula of compound  NaCl  MgCl2  AlCl3  SiCl4 PCl5   SCl2
       Boiling point °C  1470  1420  Sublimes at 1800C  60  75   60 
       Melting point °C  800  710    -70  -90  -80

      1. Give two chlorides that are liquids at room temperature. Give a reason for your answer. (2mks)
      2. Give a possible reason why AlCl3 has much lower boiling point than MgCl2 although both Aluminum and Magnesium are metals. (1mks)
  2. The table below gives standard reduction potentials for some half cells.
     Half-cell  Half-cell equation  Eθ /V
     I  Cr3+ (aq) + e- → Cr2+ (aq)  -0.41
     II  Cd2+ (aq) + 2e- → Cd (s)  -0.4
     III  Na+ (aq) + e- → Na (s)  -2.71
     IV  Cu2+ (aq) + 2e- → Cu (s)  0.34
     V  Pb2+ (aq) + 2e- → Pb (s)  -0.13
     VI  Br2 (aq) + 2e- → 2Br- (aq)  1.07
     VII  2H+(aq) + 2e- → H2(g)   0
     VIII  Fe2+(aq) + 2e- → Fe(s)  -0.44V
     IX  O2(g) + 2H2O (l) + 4e- → 4OH-(aq) +0.40V
     X  H2O2(aq) + 2H+(aq) + 2e- → 2H2O(l) +1.23V

    1. Identify with reasons: (2mks)
      1. The strongest oxidizing agent.
      2. The strongest reducing agent.
    2. Draw an electrochemical cell from half-cells V and IV. (3mks)
    3. Write the equation and calculate the electromotive force for the electrochemical cell constructed from half-cells V and IV. (2 marks)
    4. Explain why it is not advisable to use aqueous sodium sulphate as the salt bridge in the electrochemical cell formed between half-cells V and IV. (1mark)
    5. Write the cell notation for an electrochemical cell made using half-cells V and VI. (1 mark)
  3.  
    1. Draw the structures of the following compounds. (2mks)
      1. 2 – methylbut-2-ene
      2. heptanoic acid
    2. Describe a physical test that can be used to distinguish between ethanol and ethene (2mks)
    3. Use the flow chart below to answer the questions that follow.
                                ChemMocksQ8
      1. Name
        1. The type of reaction that occurs in step VII. (1mk)
        2. Substance B (1mk)
      2. What conditions and reagents are necessary to convert CH3CH2OH to CH3CH2COOCH2CH3 in step II
        Conditions (1mk)
        Reagent (1mk)
      3. Give the formula and name of substance C. (1mk)
      4. Give the reagent and conditions necessary for the reaction in step IV. (2mks)
      5.  
        1. Draw and name the structure of polymer P. (1mk)
        2. Name one use of the polymer P. (1mk)
  4. Several students prepared hydrogen gas using different reagent
    Student 1: Used Zinc granules and dil. Nitric (V) acid
    Student 2: Used Zinc granules and dilute sulphuric acid and a catalyst.
    Student 3. Used calcium and dilute sulphuric(VI) acid.
    Student 4: Used copper and dilute hydrochloric acid.
    1. State and explain the observation made in the set-ups for;
      1. Student 2. (1mk)
      2. Student 3 (2mks)
    2. Explain why no hydrogen was collect for set ups of student;
      1. 1 (1mk)
      2. 4 (1mk)
    3. Name the catalyst used by student 2. (1 mk)
    4. Write the equation for the reaction that took place in the set-up for student 2. (1mk)
    5. Explain why group 1 metals are not used to prepare hydrogen gas in the laboratory. (1mk)
    6. State two uses of hydrogen gas. (1 mk)
  5.  
    1. In an experiment to determine the heat of combustion of ethanol the following data was collected.
      Volume of water = 450cm3
      Initial temperatures of water = 25°C Final temperature of water = 46.5°C
      Mass of ethanol + lamp before heating = 125.5g
      Mass of ethanol + lamp after heating = 124.0
      Calculate:
      1. Heat evolved during the experiment (Density of water = 1g/cm3, specific heat capacity of water = 4.2kJ/kg-1k-1. (2 marks)
      2. Molar heat of combustion of ethanol. (2mks)        (C=12,O=16,H=1).
    2. Write the thermochemical equation for the complete combustion of ethanol. (1 mark)
    3. The molar heat of combustion obtained from an experiment like the one above is usually lower than the theoretical value. Explain. (2 marks)
    4. The molar heat of combustion of hydrogen is given as -286Kj/mol-2
      1. Write the thermochemical equation for the reaction.  (1 mark)
      2. Draw an energy level diagram for the reaction in d (i) above.(2 marks)
  6. In an experiment to determine the solubility of potassium chlorate, the following results were obtained.
     Total volume of water added (cm3)  10 20  30  40  50 
     Mass of potassium chlorate (g)  5 5  5  5  5 
     Temperature at which crystals appear (°C)  80 65  55  45  30 
     Solubility of potassium chlorate (g/100 H2O)          

    1. Complete the table to show the solubility of potassium chlorate at different temperatures. (3 marks)
    2. Plot a graph of mass of potassium chlorate per 100g water against temperature at which crystals from. (3 marks)
                MathsMocksQ12
    3. From the graph, determine:
      1. The solubility of potassium chlorate at 40°C. (1 mark)
      2. The temperature at which the solubility of potassium chlorate is 35g/100g water. (1 mark)
    4. Explain the shape of the graph. (1 mark)
    5. State one application of solubility and solubility curves. (1 mark)
  7. In the preparation of Copper carbonate, copper was burnt in air and the product collected. Dilute sulphuric acid was added and the mixture filtered and cooled. Sodium carbonate was added to the filtrate and the content filtered. The residue was washed and dried to give a green powder.
    1. Give the chemical name of the product formed when copper burns in air (1mk)
    2. Write a chemical equation for the formation of product. (1mk)
    3.  
      1. Name filtrate collected after sodium carbonate was added (1mk)
      2. Name the green powder. (1mk)
    4. Write chemical equation for the reaction between product in (a) and acid. (1mk)
    5. Write an ionic equation to show the formation of the green powder (1mk)
    6. Write an equation to show what happened when green powder is strongly heated. (1mk)
    7. Using a diagram, describe how a salt can be obtained from the filtrate in c(i) above. (3mks)
  8. The diagram below is a flow chart for the extraction of copper. Study it and answer the question that follow.
                             ChemMocksQ9
    1. Give the name and formula of the major ore from which copper is extracted. (1mk)
    2. Give the name of the process carried out in step II and III. (1mk)
    3. Write equation for the reactions taking place in step III and IV. (2mks)
    4. Iron (ii) oxide is an impurity during extraction of copper. Write the equation for the reaction to show how it is removed. (1mk)
    5.  
      1. Draw a well labelled diagram to show blister copper is purified to form pure copper. (2mks)
      2. Write the ionic equation for the anode and cathode reaction during purification of copper. (2 mks)

                                                                            MARKING SCHEME

  1.  
    1. 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 elements.
                                                 ChemMocksQ7
      • Which element will require the least amount of energy to remove one of the outermost electrons? (1mk)
        • V
      • Select the most reactive non- metal. (1mk)
        • S
      • Which of the elements has the greatest tendency of forming covalent? Explain (2mks)
        • Q - has four valence electrons which takes part in the bonding.
          What name is given to the family of elements to which elements O, T and V belong?(1mk)
        • Alakali metals
      • An element W has atomic number 15. Indicate the position of W on the grid.  (1mk)
        • 2.8.5
      • Explain why the atomic radius of S is smaller than that of R.  (1mks)
        • S - has a higher nuclear charge/protons than R hence pulls the outtermost energy level closer
      • Explain why the atomic radius of Z is smaller than its ionic radius. (1mk)
        • Z - gains electrons to form ions. Due to repulsion force of the incoming electrons and electrons in the energy levels of the atom.
    2. Study the information given in the table below and answer question that follow.
       Formula of compound  NaCl  MgCl2  AlCl3  SiCl4 PCl5   SCl2
       Boiling point °C  1470  1420  Sublimes at 1800C  60  75   60 
       Melting point °C  800  710    -70  -90  -80

      1. Give two chlorides that are liquids at room temperature. Give a reason for your answer. (2mks)
        • SiCl4, PCl2, SCl2 (any two)
        • Melting point below room temperaturen (25°C)
      2. Give a possible reason why AlCl3 has much lower boiling point than MgCl2 although both Aluminum and Magnesium are metals. (1mks)
        • Aluiminium chloride forms simple molecular structure
        • MgCl2 forms a giant ionic structure with strong electrosstatic forces.
  2. The table below gives standard reduction potentials for some half cells.
     Half-cell  Half-cell equation  Eθ /V
     I  Cr3+ (aq) + e- → Cr2+ (aq)  -0.41
     II  Cd2+ (aq) + 2e- → Cd (s)  -0.4
     III  Na+ (aq) + e- → Na (s)  -2.71
     IV  Cu2+ (aq) + 2e- → Cu (s)  0.34
     V  Pb2+ (aq) + 2e- → Pb (s)  -0.13
     VI  Br2 (aq) + 2e- → 2Br- (aq)  1.07
     VII  2H+(aq) + 2e- → H2(g)   0
     VIII  Fe2+(aq) + 2e- → Fe(s)  -0.44V
     IX  O2(g) + 2H2O (l) + 4e- → 4OH-(aq) +0.40V
     X  H2O2(aq) + 2H+(aq) + 2e- → 2H2O(l) +1.23V

    1. Identify with reasons: (2mks)
      1. The strongest oxidizing agent.
        H202 → most electropositive
      2. The strongest reducing agent.
        Na → most electropositive
    2. Draw an electrochemical cell from half-cells V and IV. (3mks)
        ChemMocksQ12
    3. Write the equation and calculate the electromotive force for the electrochemical cell constructed from half-cells V and IV. (2 marks)
      • Pb(s) + Cu2+(aq) → Pb2+(aq) + Cu(s) 
         + 0.34 − (− 0.13) = + 0.47V
    4. Explain why it is not advisable to use aqueous sodium sulphate as the salt bridge in the electrochemical cell formed between half-cells V and IV. (1mark)
      • Lead (ii) ions will form insoluble lead (ii) sulphate with the sulphate ions.
    5. Write the cell notation for an electrochemical cell made using half-cells V and VI. (1 mark)
      • Pb(s)Ι Pb2+(aq)ΙΙCu2+(aq)Ι Cu(s)  Eθ = +0.47V
  3.  
    1. Draw the structures of the following compounds. (2mks)
      1. 2 – methylbut-2-ene
                                           ChemMocksQ13
      2. heptanoic acid
                                   ChemMocksQ14
    2. Describe a physical test that can be used to distinguish between ethanol and ethene (2mks)
      • Burn each separately with a nono-luminous flame.
      • Ethanol burns with a blue flame
      • Etheneburns with a yellow sooty flame
    3. Use the flow chart below to answer the questions that follow.
                                ChemMocksQ8
      1. Name
        1. The type of reaction that occurs in step VII. (1mk)
        2. Substance B (1mk)
          • Chloroethane
      2. What conditions and reagents are necessary to convert CH3CH2OH to CH3CH2COOCH2CH3 in step II
        Conditions (1mk)
        • Warming 
        • Drops of Concentrated Sulphuric acid
          Reagent (1mk)
        • Propanoic acid
      3. Give the formula and name of substance C. (1mk)
        • CH3CH2ONa     Sodium ethoxide
      4. Give the reagent and conditions necessary for the reaction in step IV. (2mks)
        • Reagent ⇒ Hydrogen gas
        • Condition ⇒ Nickel/daudanium catalyst
                              150°C − 250°C (any within the range)                           
      5.  
        1. Draw and name the structure of polymer P. (1mk)
           ChemMocksQ15
        2. Name one use of the polymer P. (1mk)
          • Used as packaging bags
  4. Several students prepared hydrogen gas using different reagent
    Student 1: Used Zinc granules and dil. Nitric (V) acid
    Student 2: Used Zinc granules and dilute sulphuric acid and a catalyst.
    Student 3. Used calcium and dilute sulphuric(VI) acid.
    Student 4: Used copper and dilute hydrochloric acid.
    1. State and explain the observation made in the set-ups for;
      1. Student 2. (1mk)
        • More bubbbling/effervescence occurred
        • Vigorous reaction due to the presence of catalyst that speeds up the reaction.
      2. Student 3 (2mks)
        • Bubbling occured and then stopped
        • Due to formation of insoluble CaSo4 that coats the calcium
    2. Explain why no hydrogen was collect for set ups of student;
      1. 1 - Hydrogen gas produced was oxidised by dilute nitric (v) acid to water (1mk)
      2. 4 - Copper is less raective than hydrogen hence cannot displace it(1mk)
    3. Name the catalyst used by student 2. (1 mk)
      • Crystals copper(ii) sulphate
    4. Write the equation for the reaction that took place in the set-up for student 2. (1mk)
      • Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)
    5. Explain why group 1 metals are not used to prepare hydrogen gas in the laboratory. (1mk)
      • Will react with dilute acids explosively
    6. State two uses of hydrogen gas. (1 mk)
      • Manufacture of margarine
      • As rocket fuel
      • Manufacture of ammonia
      • In oxy-hydrogen flame
      • In weather ballons
  5.  
    1. In an experiment to determine the heat of combustion of ethanol the following data was collected.
      Volume of water = 450cm3
      Initial temperatures of water = 25°C Final temperature of water = 46.5°C
      Mass of ethanol + lamp before heating = 125.5g
      Mass of ethanol + lamp after heating = 124.0
      Calculate:
      1. Heat evolved during the experiment (Density of water = 1g/cm3, specific heat capacity of water = 4.2kJ/kg-1k-1. (2 marks)
         450 x 4.2 x 21.5 = − 40.635kJ
        1000
      2. Molar heat of combustion of ethanol. (2mks)        (C=12,O=16,H=1).
        Mass of ethanol = 1.5g
        RMM of ethanol ⇒ C2H5OH = 24 + 6 + 16 = 46
        1.5g → 40.635KJ
        4.6g →   
        4.6 x 40.635 = 1246.14KJ/mol
                 1.5                       
    2. Write the thermochemical equation for the complete combustion of ethanol. (1 mark)
      C2H5OH(l) + 3O2(g) → CO2(g) + H2O   ΔH = −1246.14 KJ/mol
    3. The molar heat of combustion obtained from an experiment like the one above is usually lower than the theoretical value. Explain. (2 marks)
      1. Some of the heat produced was absorbed by the apparatus
      2. Some heat got lost to the sorrounding environments
    4. The molar heat of combustion of hydrogen is given as -286Kj/mol-2
      1. Write the thermochemical equation for the reaction.  (1 mark)
        H2(g) + ½O2(g) → 2H2O    ΔH = − 286kJ/mol
      2. Draw an energy level diagram for the reaction in d (i) above.(2 marks)
               ChemMocksQ16
  6. In an experiment to determine the solubility of potassium chlorate, the following results were obtained.
     Total volume of water added (cm3)  10 20  30  40  50 
     Mass of potassium chlorate (g)  5 5  5  5  5 
     Temperature at which crystals appear (°C)  80 65  55  45  30 
     Solubility of potassium chlorate (g/100 H2O)  50 25  16.7  12.5  10 

    1. Complete the table to show the solubility of potassium chlorate at different temperatures. (3 marks)
    2. Plot a graph of mass of potassium chlorate per 100g water against temperature at which crystals from. (3 marks)
                MathsMocksQ12
    3. From the graph, determine:
      1. The solubility of potassium chlorate at 40°C. (1 mark)
        • 12g/100gH2O
      2. The temperature at which the solubility of potassium chlorate is 35g/100g water. (1 mark)
        • 72°C
    4. Explain the shape of the graph. (1 mark)
      • Solubility increase with increase in temperature
    5. State one application of solubility and solubility curves. (1 mark)
      • Fractional distillation
  7. In the preparation of Copper carbonate, copper was burnt in air and the product collected. Dilute sulphuric acid was added and the mixture filtered and cooled. Sodium carbonate was added to the filtrate and the content filtered. The residue was washed and dried to give a green powder.
    1. Give the chemical name of the product formed when copper burns in air (1mk)
      • Copper (iv) oxide
    2. Write a chemical equation for the formation of product. (1mk)
      • 2Cu(s) + O2(g) → 2CuO(s)
    3.  
      1. Name filtrate collected after sodium carbonate was added (1mk)
        • Sodium sulphate
      2. Name the green powder. (1mk)
        • Copper (ii) carbonate
    4. Write chemical equation for the reaction between product in (a) and acid. (1mk)
      • CuO(s) + H2SO4(aq) → CuSO4 + H2O(s)
    5. Write an ionic equation to show the formation of the green powder (1mk)
      • Cu2+(aq) + CO2−3(aq) → CuCO3(s)
    6. Write an equation to show what happened when green powder is strongly heated. (1mk)
      • CuCO3(s) → CuO(s) + CO2(g)
    7. Using a diagram, describe how a salt can be obtained from the filtrate in c(i) above. (3mks)
                                                            ChemMocksQ18
  8. The diagram below is a flow chart for the extraction of copper. Study it and answer the question that follow.
                             ChemMocksQ9
    1. Give the name and formula of the major ore from which copper is extracted. (1mk)
      • Copper pyrites CuFeS2
    2. Give the name of the process carried out in step II and III. (1mk)
      I - Froth floatation
      II - Roasting
    3. Write equation for the reactions taking place in step III and IV. (2mks)
      • 2 CuFeS2(s) + 3O2(g) → 2Cu2S(s) + 2FeO(s) + 2SO2(g)
      • 2Cu2S(s) + 2CuO → 6Cu + SO2
    4. Iron (ii) oxide is an impurity during extraction of copper. Write the equation for the reaction to show how it is removed. (1mk)
      • FeO(s) + SiO2(s) → FeSiO3
    5.  
      1. Draw a well labelled diagram to show blister copper is purified to form pure copper. (2mks)
                    ChemMocksQ19
      2. Write the ionic equation for the anode and cathode reaction during purification of copper. (2 mks)
        • Cu(s) → Cu2+(aq) + 2e− Anode
        • Cu2+ 2e− → Cu(s) Cathode

 

 

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