Chemistry Paper 2 - 2020 MOKASA JOINT MOCKS EXAMINATION (QUESTIONS AND ANSWERS)

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  1.  
    1. The setup below was used to investigate the reaction between metals and water.

      1achemp2

      1. Identify solid X and state its purpose.
        Solid X . (½ mark)
        Purpose (½ mark)
      2. Write a chemical equation for the reaction that produces the flame. (1 mark)
    2. The set-up below was used to investigate the properties of hydrogen.

      1bchemp2

      1. On the diagram, indicate what should be done for the reaction to occur. (1 mark)
      2. Hydrogen gas is allowed to pass through the tube for some time before it is lit. Explain. (1 mark)
      3. Write an equation for the reaction that occurs in the combustion tube. (1 mark)
      4. When the reaction is complete, hydrogen gas is passed through the apparatus until it cools down. Explain. (2 marks)
      5. What property of hydrogen is being investigated? (1 mark)
      6. What observation confirms the property stated in (v) above? (1 mark)
      7. Why is zinc oxide not used to investigate this property of hydrogen gas?(1 mark)
  2.  
    1. The diagram below represents an incomplete set-up of apparatus that can be used to prepare and collect dry carbon (iv) oxide gas. Complete the diagram and answer the questions that follow.
      2achemp2
      1. Complete the above diagram. (3 marks)
      2. Identify liquid R. .. (1mark)
      3. Write the equation for the reaction taking place in the flask S. (1 mark)
      4. Explain why it is not advisable to use lead (II) carbonate in place of marble chips. (1 mark)
    2. The diagram below is used to investigate the effect of carbon (II) oxide on lead (II) oxide. Study it and answer the questions that follow.

      2bchemp2

      1. Write an equation for the laboratory preparation of carbon (II) oxide. (1 mark)
      2. State and explain the observation in the combustion tube M. (2 marks)
      3. Identify liquid K and state its function. (1 mark)
      4. Why is it necessary burn excess gas at L. (1 mark)
  3.  
    1. Name the following organic compounds.
      1. CH3COOCH2CH3 (1mark)
      2. CH3CH2CHCCHCH2CH3 (1mark)
    2. Study the flow diagram below and use it to answer the questions that follow.

      3bchemp2

      1. Name the compounds;
        U _____ (½ mark)
        Gas X _____ (½ mark)
        Intermediate Y ________ (½ mark)
      2. Name the process which leads to the formation of substance Z from the intermediate Y. (1 mark)
      3. Identify the reagent and the condition for step 1
        Reagent (1 mark)
        Condition . (1 mark)
      4. State one disadvantage for the continued use of items made from compound formed in step 3. (1 mark)
      5. Write a balanced equation for the reaction taking place in step 2. (1 mark)
    3. Below are structures of two cleaning agents
      R – COO-Na+ ---- A
      3cchemp2

      1. Identify the cleaning agent suitable to be used in water containing calcium chloride. (1 mark)
      2. State one advantage of using cleaning agent A. (1 mark)
      3. Name the cleaning agent A. (½ mark)
    4. Ethanol is an important organic solvent. It can be prepared by the fermentation of glucose, C6H12O6. Give two conditions necessary or the reaction to take place. (1 mark)
  4.  
    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.

      4chemp2

      1. Identify the most reactive non-metal. Explain. (2 marks)
      2. What is the name given to the family of elements of which I and J belong? . (½ mark)
      3. Using dots (•) and crosses (×) to represent electrons, show bonding in the compound formed between C and H. (2 marks)
      4. How does the atomic radius of F compare with that of I. Explain. (2 marks)
    2. Study the table below and answer the questions that follow.

      Substance  M N O P Q R
      M.Pt. °C 801 1356 -101 26 -39 113
      B.Pt °C 1410 2850 -36 154 457 445
      Electrical conductivity in solid state Poor Poor Poor Poor Good Poor
      Electrical conductivity in molten state Good Poor Poor Poor Good Poor


      1. Explain why substance M is a good conductor in molten state and not in solid state. (2 marks)
      2. What is the most likely structure of substance N. Explain. (1 ½ marks)
      3. Identify, with reasons, a substance that exists as a liquid at room temperature. . (2 marks)
  5. The flow chart below shows a sequence of reaction involving a mixture of two salts, mixture M. Study it and answer the questions that follow.

    5chemp2

    1.  
      1. write the formula of the following:
        1. Anion in solid Q (1 mark)
        2. The two salts present in mixture M. (2 marks)
      2. Write an ionic equation for the reaction in step VI. (1 mark)
      3. State and explain two observations made in step V. (3 marks)
    2.  
      1. You are provided with copper solid, sodium carbonate solid, dilute hydrochloric acid, distilled water and dilute nitric (v) acid. Describe how you can prepare crystals of copper (II) carbonate. (3 marks)
      2. Name the industrial process by which the sodium carbonate used in II (a) above can be obtained. (1 mark)
  6.  
    1. From an experiment, 25.0cm3 of hydrochloric acid required 20.0cm3 of 0.02M sodium carbonate for a complete reaction. Calculate:
      1. The number of moles of sodium carbonate used. (1 mark)
      2. The number of moles of hydrochloric acid used. (1 mark)
      3. The molarity of the acid. (1 mark)
    2. A solution of sodium hydroxide was found to contain 12.4g/dm3 of sodium hydroxide. 25cm3 of this solution reacted with 15cm3 of a solution of sulphuric (VI) acid. (Na=23.0, H=1.0, S=32.0, O=16.0)
      1. Find the molarity of the sodium hydroxide solution. (1 mark)
      2. Calculate the number of moles of sodium hydroxide solution used. (1 mark)
      3. Calculate the number of moles of the acid used. (2 marks)
      4. Determine the concentration of the sulphuric (VI) acid solution in g/dm3. . (3marks)
    3.  
      1. State the Charles law. (1 mark)
      2. A certain mass of gas occupies 146 dm3 at 291K and 98.31 kPa. What will be its temperature if its volume is reduced to 133dm3 at 101.325 kPa? (2 marks)
  7.  
    1. Define a saturated solution. (1 mark)
    2. The table below represent the solubilities of sodium nitrate and Sulphur (IV) oxide at different temperatures.

      Temperature ( oC) 10 18 26 34 42

      Solubility of sodium nitrate ( g/ 100g of water)

      20 29 40 53 68

      Solubility of sulphur ( IV) oxide ( g/ 100g of water)

      78 55 45 40 36


      On the grid provided below, plot a graph of solubilities of sodium nitrate and Sulphur (IV) oxide against temperature. (4 marks)

      Using the graph;
      1. Determine the solubility of Sulphur (IV) oxide at 16o (½ mark)
      2. The concentration, in moles per litre, of sodium nitrate at 16o C (assume density of solution is 1 g/cm3) (Na=23, 0=16, N=14). (3 marks)
      3. Mass of crystals formed when a solution of sodium hydroxide is cooled from 40oC to 26oC (2 marks)
      4. What is the relationship between solubility of sodium nitrate and temperature? (1 mark)
    3. Give one advantage of hard water. (½ mark)
    4. Explain why the reaction between 1g of sodium carbonate with 2M hydrochloric acid is faster than between 1g of sodium carbonate with 2M ethanoic acid. (1 mark)


Marking Scheme

  1.  
    1. The setup below was used to investigate the reaction between metals and water.

      1achemp2

      1. Identify solid X and state its purpose. 
        Solid X . (½ mark)

        Anhydrous Calcium Chloride/calcium oxide

        Purpose (½ mark)

        To dry the hydrogen gas.

      2. Write a chemical equation for the reaction that produces the flame. (1 mark)

        2H2(g) + O2(g) -> 2H2O(g)

    2. The set-up below was used to investigate the properties of hydrogen.

       1bchemsp2

      1. On the diagram, indicate what should be done for the reaction to occur. (1 mark)
      2. Hydrogen gas is allowed to pass through the tube for some time before it is lit. Explain. (1 mark)

        to drive away air to avoid an explosion

      3. Write an equation for the reaction that occurs in the combustion tube. (1 mark)

        CuO(s) + H2(g) -> Cu(s) + H2O(l)

      4. When the reaction is complete, hydrogen gas is passed through the apparatus until it cools down. Explain. (2 marks)

        so as to avoid re-oxidation of the hot copper metal by oxygen in the air.

      5. What property of hydrogen is being investigated? (1 mark)

        Reducing property

      6. What observation confirms the property stated in (v) above? (1 mark)

        black CuO turns to brown Cu solid / A colourless liquid is formed

      7. Why is zinc oxide not used to investigate this property of hydrogen gas?(1 mark)

        Zinc is above hydrogen in the reacrivity series/more reactive hence Hydrogen cannot displace Zinc.
  2.  
    1. The diagram below represents an incomplete set-up of apparatus that can be used to prepare and collect dry carbon (iv) oxide gas. Complete the diagram and answer the questions that follow.

      2chemsp2

      1. Complete the above diagram. (3 marks)
      2. Identify liquid R. .. (1mark)

        dilute hydrochloric acid.

      3. Write the equation for the reaction taking place in the flask S. (1 mark)

        CaCO3(s) + 2HCl(aq) -> CaCl2(aq) + CO2(g) + H2O(l)

      4. Explain why it is not advisable to use lead (II) carbonate in place of marble chips. (1 mark)

        Lead II Carbonate forms insoluble salt of Lead II Chloride which coats the carbonate preventing further reaction.

    2. The diagram below is used to investigate the effect of carbon (II) oxide on lead (II) oxide. Study it and answer the questions that follow.

      2bchemp2

      1. Write an equation for the laboratory preparation of carbon (II) oxide. (1 mark)

        HCOOH(s) -H2SO4(l)-> CO3 + H2O(l)

        H2C2O4 -conc H2SO4-> CO(g) + CO2(g) + H2O(l)

      2. State and explain the observation in the combustion tube M. (2 marks)

        Orange solid turns grey. CO reduces hot Lead II Oxide to form lead metal.

      3. Identify liquid K and state its function. (1 mark)

        Calcium hydroxide to absorb the CO2 formed when CO is oxidized.

      4. Why is it necessary burn excess gas at L. (1 mark)

        CO is poisonous hencee should not be released into the atmosphere.
  3.  
    1. Name the following organic compounds.
      1. CH3COOCH2CH3 (1mark)

        Ethylethanoate

      2. CH3CH2CHCCHCH2CH(1mark)

        Hept-3,4-diene


    2. Study the flow diagram below and use it to answer the questions that follow.

      3bchemp2

      1. Name the compounds;

        U - Potassium Ethoxide (½ mark)
        Gas X - Carbon (IV) Oxide (½ mark)
        Intermediate Y - Ethyl Hydrogen Sulphate (½ mark)

      2. Name the process which leads to the formation of substance Z from the intermediate Y. (1 mark)

        Hydrolysis

      3. Identify the reagent and the condition for step 1

        Reagent - Concentrated sulphuric VI acid (1 mark)
        Condition - Heating upto 160oC - 180oC. (1 mark)

      4. State one disadvantage for the continued use of items made from compound formed in step 3. (1 mark)

        Causes environmental pollution as it is non biodegradable and produces poisonous gases when burnt.

      5. Write a balanced equation for the reaction taking place in step 2. (1 mark)

        2C2H5OH(l) -> 2K(s) -> 2C2H5OK(aq) + H2(g)


    3. Below are structures of two cleaning agents
      R – COO-Na+ ---- A
      3cchemp2
      1. Identify the cleaning agent suitable to be used in water containing calcium chloride. (1 mark)

        B

      2. State one advantage of using cleaning agent A. (1 mark)

        Forms scum with hard water / Not readily lather hard water

      3. Name the cleaning agent A. (½ mark)

        Soapy detergent/Soap

    4. Ethanol is an important organic solvent. It can be prepared by the fermentation of glucose, C6H12O6. Give two conditions necessary or the reaction to take place. (1 mark)

      Warming up to 30oC
      yeast

  4.  
    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.

      4chemp2

      1. Identify the most reactive non-metal. Explain. (2 marks)

        Most electronegative / has smallest atomic radius hence readily gains electrons.

      2. What is the name given to the family of elements of which I and J belong? . (½ mark)

        Halogens

      3. Using dots (•) and crosses (×) to represent electrons, show bonding in the compound formed between C and H. (2 marks)
      4. How does the atomic radius of F compare with that of I. Explain. (2 marks)

        I has smaller atomic radius than F. I has more proton than F hance stronger nuclear charge than F.

    2. Study the table below and answer the questions that follow.
      Substance  M N O P Q R
      M.Pt. °C 801 1356 -101 26 -39 113
      B.Pt °C 1410 2850 -36 154 457 445
      Electrical conductivity in solid state Poor Poor Poor Poor Good Poor
      Electrical conductivity in molten state Good Poor Poor Poor Good Poor
      1. Explain why substance M is a good conductor in molten state and not in solid state. (2 marks)

        In solid state, ions of M are in fixed positions.
        In molten state, ions are mobile.

      2. What is the most likely structure of substance N. Explain. (1 ½ marks)

        Grant atomic/covalent structure
        N has highest melting and boiling points due to uniformly of strong covalent bonds.

      3. Identify, with reasons, a substance that exists as a liquid at room temperature. . (2 marks)

        Its melting point is lower than room temperature and boiling point higher than room temperature.

  5. The flow chart below shows a sequence of reaction involving a mixture of two salts, mixture M. Study it and answer the questions that follow.

    5chemp2

    1.  
      1. write the formula of the following:
        1. Anion in solid Q (1 mark)

          O2-(aq)

        2. The two salts present in mixture M. (2 marks)

          ZnSO4
          CuCO3

      2. Write an ionic equation for the reaction in step VI. (1 mark)

        Ba2+(aq) + SO42-(aq) -> BaSO4(s)

      3. State and explain two observations made in step V. (3 marks)

        - Blue color of solution fades
        - Deposits of red-brown solids.
        Magnesium displaces copper II ions since it is more reactive than copper.


    2.  
      1. You are provided with copper solid, sodium carbonate solid, dilute hydrochloric acid, distilled water and dilute nitric (v) acid. Describe how you can prepare crystals of copper (II) carbonate. (3 marks)

        Clean copper metal using dilute HCl(aq)
        React excess copper with dilute HNO3, filter and retain the filtrate.
        Add distilled water to NaCO3, Stir to obtain Na2CO3 solution.
        Add Cu(NO3)2(aq) to Na2CO2(aq) to obtain CuCO3(s) and NaNO3(aq)
        Filter to obtain CuCO3(s) residue. Wash the residue with distilled water and dry between filter papers.


      2. Name the industrial process by which the sodium carbonate used in II (a) above can be obtained. (1 mark)

        Solvay process
  6.  
    1. From an experiment, 25.0cm3 of hydrochloric acid required 20.0cm3 of 0.02M sodium carbonate for a complete reaction. Calculate:
      1. The number of moles of sodium carbonate used. (1 mark)
        6aichemsp2
      2. The number of moles of hydrochloric acid used. (1 mark)
        6aiichemsp2
      3. The molarity of the acid. (1 mark)
        6aiiichemsp2
    2. A solution of sodium hydroxide was found to contain 12.4g/dm3 of sodium hydroxide. 25cm3 of this solution reacted with 15cm3 of a solution of sulphuric (VI) acid. (Na=23.0, H=1.0, S=32.0, O=16.0)
      1. Find the molarity of the sodium hydroxide solution. (1 mark)
        6bichemsp2
      2. Calculate the number of moles of sodium hydroxide solution used. (1 mark)
        6biichemsp2
      3. Calculate the number of moles of the acid used. (2 marks)
        6biiichemsp2
      4. Determine the concentration of the sulphuric (VI) acid solution in g/dm3. . (3marks)
        6bvchemsp2
    3.  
      1. State the Charles law. (1 mark)

        The volume of a fixed mass of gas is directly proportional to its absolute temperature at constant pressure.

      2. A certain mass of gas occupies 146 dm3 at 291K and 98.31 kPa. What will be its temperature if its volume is reduced to 133dm3 at 101.325 kPa? (2 marks)

        6ciichemsp2
  7.  
    1. Define a saturated solution. (1 mark)

      A solution that cannot dissolve anymore solute at a particular temperature.

    2. The table below represent the solubilities of sodium nitrate and Sulphur (IV) oxide at different temperatures.
      Temperature ( oC) 10 18 26 34 42

      Solubility of sodium nitrate ( g/ 100g of water)

      20 29 40 53 68

      Solubility of sulphur ( IV) oxide ( g/ 100g of water)

      78 55 45 40 36

      On the grid provided below, plot a graph of solubilities of sodium nitrate and Sulphur (IV) oxide against temperature. (4 marks)


      7bchemsp2

      Using the graph;

      1. Determine the solubility of Sulphur (IV) oxide at 16o (½ mark)

        58g/100g of water. (must show on the graph)


      2. The concentration, in moles per litre, of sodium nitrate at 16o C (assume density of solution is 1 g/cm3) (Na=23, 0=16, N=14). (3 marks)
        7biichemsp2
      3. Mass of crystals formed when a solution of sodium hydroxide is cooled from 40oC to 26oC (2 marks)
        7biiichemsp2
      4. What is the relationship between solubility of sodium nitrate and temperature? (1 mark)

        As temperature increases, solubility of NaNO3 increases.

    3. Give one advantage of hard water. (½ mark)

      Provides calcium essential nutrient / used in brewing

    4. Explain why the reaction between 1g of sodium carbonate with 2M hydrochloric acid is faster than between 1g of sodium carbonate with 2M ethanoic acid. (1 mark)

      HCl is a strong acid, CH3COOH is a weak acid. CH3COOH partially dissociates while HCL dissociates fully. Some energy is used in fully ionising CH3COOH.

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