Chemistry Paper 1 Questions and Answers - Moi Kabarak High School Mock 2020/2021

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INSTRUCTIONS TO STUDENTS

  • Answer ALL the questions in the spaces provided.
  1. State the process that takes place when;             (3 marks)
    1. Natural fats or oils are hydrolysed using alkalis.
    2. Sulphur is added to natural rubber and heated to form cross links
    3. A heavy nuclide is broken down by a fast moving neutron.
  2. The atomic number of element A is 11 and that of B is 8.
    1. Write down the possible formulae of the compound formed between A and B.  (1 mark)
    2. Draw a diagram using dots(•) and crosses (x) to show the bonding in the compound formed.   (1 mark)
  3. An element has isotopic species A and B each with a mass number 39 and 40 respectively. The percentage of A is 60% and B is 40% for an isotopic element X. Calculate the relative atomics mass of X. (2 marks)
  4.  
    1. Define the term solubility.  (1 mark)
    2. 70g of salt W were added to 80cm3 of water at 25°C. After stirring 10g of crystals of salt were filtered out. Determine the solubility of salt W at 25°C.    (2 marks)
  5.  
    1. Define molar heat solution.   (1 mark)
    2. The lattice energy of sodium bromide and hydration energies of sodium and bromide ions are 733,406 and 335kj/mol respectively.
      1. Determine the heat of solution of sodium bromide. (1 mark)
      2. Sketch an energy level diagram of the process.       (2 marks)
  6. The table below gives some experimental results on four samples of water. Use the information to answer the questions that follow.
        Drops of soap needed to form lather  
     Sample of water (50cm2)  Before boiling  After boiling
     A          25         15
     B           8          8
     C          18          8
     D          25         25
    1. Which sample(s) contain permanent hardness? Explain.    (1½ marks)
    2. Which samples are likely to contain calcium hydrogen carbonate? Explain.  (1½marks)
  7. Describe how you would prepare dry sample of lead (II) chloride starting with lead (II) carbonate.  (3 marks)
  8.  The following elements belong to the same group of periodic table. (Letters do not represent the actual symbols)
     element   Atomic radius (nm)   lonic radius (nm)   First ionization
    (KJ mol-1
     P    0.137      0.066      736
     Q    0.089      0.031      900
     R    0.174      0.099      590

    1. State whether the elements are metals or non-metals. Explain your answer.   (2 marks)
    2. Which element is the most reactive? Explain.      (2 marks)
  9. An aqueous solution of hydrogen chloride can be prepared as shown in the diagram below.
             Preparation of aqueous solution of hydrogen chloride
    1. Give two reasons for using an inverted funnel.   (1 mark)
    2. Few drops of Lead (II) nitrate solution were added to 4cm3 of the solution obtained above, followed by excess aqueous ammonia. Explain the observation made.    (2 marks)
  10. Nitrogen reacts with oxygen according to the equation.
    N2(g) + O2(g) double arrows  2NO(g),∆H = +197KJ/mole
    What is the effect of increase of the following on the position of the equilibrium?
    Explain.
    1. Pressure  (1½ marks)
    2. Temperature   (1½ marks)
  11. The standard reduction potentials of two half cells are;
    Ag+(aq) + e  →  Ag(s) ; Eθ = +0.80v
    Mg2+(aq) + 2e−   → Mg(s) Eθ = −2.37
    1. Draw a well labelled diagram of an electrochemical cell that can be constructed using the two half cells.
      (2 marks)
    2. Determine the e.m.f of the above cell.  (1 mark)
  12. A white solid L changes to yellow Solid R when strongly heated but on cooling becomes white again. When L is reacted with dilute nitric(v) acid effervescence occurs.
    1. Identify L.     (1 mark)
    2. Write the equation for the reaction of L and nitric(v) acid.    (1 mark)
    3. Name and write the formula of the salt formed when solid R dissolved in sodium hydroxide solution.
      (2 marks)
  13. Study the experimental set up of apparatus shown below.
            Studying experimental set up of an apparatus
    1. State the observation made in the combustion tube as the experiment progressed.   (1 marks)
    2. Using an equation, explain the change that occurred in the conical flask after a long time.  (2 marks)
    3. Why was the gas burned at point x?   (1 mark)
  14. The table below shows the pH values of solution J to N. 
     Solution   J    K   L    M   N 
     pH  5  13   2  10   7
    Which solution
    1. contains the largest concentration of hydroxide ions? Explain. (1 mark)
    2. is likely to be a solution of ethanoic acid? Explain. (1 mark)
  15.  
    1. Using dots (•) and crosses (x) show bonding in; (C = 2, 0 = 16, H = 1)     (2 marks)
      1. Water
      2. Carbon(IV) oxide
        (b)
    2. Why is water a liquid at room temperature while carbon (IV) oxide is a gas at room temperature? (1 mark)
  16. A gaseous compound consists of 86% carbon and 14% hydrogen by mass. At s.t.p, 3.2dm3 of the compound has a mass of 6g. (C = 12 H = 1 molar gas volume at s.t.p = 22.4dm3)
    1. Calculate its empirical formula   (1 mark)
    2. Calculate its molecular formula      (2 marks)
  17.  
    1. Identify the following cleansing agents.
      1. CH3(CH2)12CH2 -COO-Na+
      2. Cleansing agent
    2. Which cleansing agent is more suitable for washing in water containing magnesium sulphate.   (1 mark)
    3. State one advantage of using the cleansing agent in (b) above.     (1 mark)
  18. The structure below represents a segment of a polymer. Use it to answer the questions that follow.
             Structure representing segments of a monomer
    1. Draw the structure of the monomer.  (1 mark)
    2. Given that the molecular mass of the polymer is 21000 find the value of n.  (2 marks)
  19. 50cm3 of oxygen gas diffused through a porous plug in 80 secs. How long will it take 100cm3 of sulphur (IV) oxide to diffuse through the same plug? (S = 32 0= 16)      (3 marks)
  20. When a current of 0.5 amperes was passed for 32 minutes and 10 seconds through fused chloride of metal P 0.44 of P was deposited. Determine the charge of the ion of metal P. (IF = 96,500C, P =88)       (3 marks)
  21. When calcium carbonate was added to a solution of dry hydrogen chloride in methyl benzene there was no observable reaction. Explain.    (2 marks)
  22. Study the set up below and answer the questions that follow.
             Studying a set up
    1. Explain why it is important to heat the water before heating the magnesium ribbon.    (1 mark)
    2. Name gas P.       (1 mark)
    3. Write a balanced equation for the reaction which takes place in the combustion tube.     (1 mark)
  23. The chief ore of aluminium is bauxite which mainly contains Al2O3.2H20. The ore is initially purified before aluminium is extracted electrolitically.
    1. Identify the main impurities associated with this ore.      (1 mark)
    2. Sodium hydroxide solution is used in the purification process. State its role.     (1 mark)
    3. Given an equation for the reaction that forms Aluminium oxide (Alumina) from aluminium hydroxide.
      (1 mark)
  24. 3g of 257Lr whose half-life is 8 days, remains after undergoing radioactive decay for 32 days. Find the original amount of substance.         (2 marks)
  25. Study the flow chart below and answer the questions that follow.
             Studying a flow chart
    1. Identify solution P.    (1 mark)
    2. Write a chemical equation to show how solid R is formed.     (1 mark)
    3. State the observation made in process II.      (1 mark)
  26. If 25.0cm3 of 0.1 MH2S04 solution neutralized a solution containing 1.06g of sodium carbonate in 250cm3 of solution, calculate,
    1. The molarity of sodium carbonate solution (Na=23, 0=16,C=12)       (1½marks)
    2. Volume of sodium carbonate solution used.   (1½ marks)


Marking Scheme

  1. State the process that takes place when;             (3 marks)
    1. Natural fats or oils are hydrolysed using alkalis.
      • Saponification
    2. Sulphur is added to natural rubber and heated to form cross links
      • Vulcanization
    3. A heavy nuclide is broken down by a fast moving neutron.
      • Nuclear fission
  2. The atomic number of element A is 11 and that of B is 8.
    1. Write down the possible formulae of the compound formed between A and B.  (1 mark)
      • A2B
    2. Draw a diagram using dots(•) and crosses (x) to show the bonding in the compound formed.   (1 mark)
      Diagram on bonding of a certain compound
  3. An element has isotopic species A and B each with a mass number 39 and 40 respectively. The percentage of A is 60% and B is 40% for an isotopic element X. Calculate the relative atomics mass of X. (2 marks)
    R.A.M = (39×60)+(40×40)   ✓½
                          100
                  2340 + 1600     ✓½
                        100
              = 3940    ✓½
                  100
              =39.40    ✓½
  4.  
    1. Define the term solubility.  (1 mark)
      • Amount of solute that can form a saturated Solution 100g of water at a given temperature.
    2. 70g of salt W were added to 80cm3 of water at 25°C. After stirring 10g of crystals of salt were filtered out. Determine the solubility of salt W at 25°C.    (2 marks)
      70−10 =60g
      If 60g → 80g of water
         ?     → 100g of water
         = 60×100
                80
         =75g/100g of water
         
  5.  
    1. Define molar heat solution.   (1 mark)
      • The amount of heat change involved when one mole of a solute completely dissolves in water/solvent.
    2. The lattice energy of sodium bromide and hydration energies of sodium and bromide ions are 733,406 and 335kj/mol respectively.    (1 mark)
      1. ∆Hsol=Hlatt + Hhyd
        =+733 + (−406 + −335)

        =−8KJ/mole
      2. Sketch an energy level diagram of the process.       (2 marks)
        Energy level diagram of process of heating sodium bromide solution
  6. The table below gives some experimental results on four samples of water. Use the information to answer the questions that follow.
        Drops of soap needed to form lather  
     Sample of water (50cm2)  Before boiling  After boiling
     A          25         15
     B           8          8
     C          18          8
     D          25         25
    1. Which sample(s) contain permanent hardness? Explain.    (1½ marks)
      • B and D ✓1
        The drops of soap needed to form lather✓½ remain the same/did not change even after boiling.
    2. Which samples are likely to contain calcium hydrogen carbonate? Explain.  (1½marks)
      • A and C✓1
        The drops of soap needed to form lather decreased after boiling.✓½
  7. Describe how you would prepare dry sample of lead (II) chloride starting with lead (II) carbonate.  (3 marks)
    • To some amount of dilute nitric(v)acid✓½in a beaker
    • Add lead(II)carbonate as you stir till in excess✓½
    • Filter✓½ to obtain lead (II) nitrate as filtrate
    • Add some sodium chloride solution✓½/any other soluble chloride to lead(II)nitrate solution
    • Filter✓½ to obtain lead(II)chloride as residue
    • Wash the residue with distilles water and dry between filter paper✓½
  8.  The following elements belong to the same group of periodic table. (Letters do not represent the actual symbols)
     element   Atomic radius (nm)   lonic radius (nm)   First ionization
    (KJ mol-1
     P    0.137      0.066      736
     Q    0.089      0.031      900
     R    0.174      0.099      590

    1. State whether the elements are metals or non-metals. Explain your answer.   (2 marks)
      • Metals✓1
        They have smaller ionic radius than atomic radius✓1
    2. Which element is the most reactive? Explain.      (2 marks)
      • R✓1
        It has largest atomic radius hence lose electrons most easily✓1
  9. An aqueous solution of hydrogen chloride can be prepared as shown in the diagram below.
             Preparation of aqueous solution of hydrogen chloride
    1. Give two reasons for using an inverted funnel.   (1 mark)
      • To prevent the suck back
      • To increase the surface area over which the gas dissolves in water
    2. Few drops of Lead (II) nitrate solution were added to 4cm3 of the solution obtained above, followed by excess aqueous ammonia. Explain the observation made.    (2 marks)
      • A white precipitate is formed
      • Pb2+ ions react with Clions to form the insoluble PbCl2
  10. Nitrogen reacts with oxygen according to the equation.
    N2(g) + O2(g) double arrows  2NO(g),∆H = +197KJ/mole
    What is the effect of increase of the following on the position of the equilibrium?
    Explain.
    1. Pressure  (1½ marks)
      • No effect
        The number of molecules on both sides of the reaction are the same/total volumes of reactants and products are equal.
    2. Temperature  (1½ marks)
      • Shifts to the right
        Forward reaction is favoured as an endothermic process will proceed.
  11. The standard reduction potentials of two half cells are;
    Ag+(aq) + e  →  Ag(s) ; Eθ =+0.80v
    Mg2+(aq) + 2e−   → Mg(s) Eθ = −2.37
    1. Draw a well labelled diagram of an electrochemical cell that can be constructed using the two half cells.
      (2 marks)
      Labelled diagram of Electrochemical cellusing half cells
    2. Determine the e.m.f of the above cell.  (1 mark)
      e.m.f = Eθred −  Eθoxide
              =+0.80 −(−2.37)
              =+3.17v
  12. A white solid L changes to yellow solid R when strongly heated but on cooling becomes white again. When L is reacted with dilute nitric(v) acid effervescence occurs.
    1. Identify L.     (1 mark)
      ZnCO3/Zinc Carbonate
    2. Write the equation for the reaction of L and nitric(v) acid.    (1 mark)
      ZnCO3(s) +2HNO3(aq) → Zn(NO3)2(aq) +CO2(g) +H2O(l)
    3. Name and write the formula of the salt formed when solid R dissolved in sodium hydroxide solution.
      (2 marks)
      • Sodium Zincate
        Na2ZnO2
  13. Study the experimental set up of apparatus shown below.
            Studying experimental set up of an apparatus
    1. State the observation made in the combustion tube as the experiment progressed.   (1 marks)
      • Black Copper(II)Oxide changes to red brown copper.
    2. Using an equation, explain the change that occurred in the conical flask after a long time.  (2 marks)
      Ca(OH)2(aq) + CO2(g) → CaCO3(s) + H2O(l)
      CaCO3(s) +H2O(l) + CO2(g) → Ca(HCO3)2(aq)
      White precipitate which dissolves in excess CO2
    3. Why was the gas burned at point x?   (1 mark)
      • To prevent CO from escaping to the atmosphere hence polluting it as it is poisonous.
  14. The table below shows the pH values of solution J to N. 
     Solution   J    K   L    M   N 
     pH  5  13   2  10   7
    Which solution
    1. contains the largest concentration of hydroxide ions? Explain. (1 mark)
      • K
        It is a strong alkali which dissociate completely in water.
    2. is likely to be a solution of ethanoic acid? Explain. (1 mark)
      • J
        It is a weak acid
  15.  
    1. Using dots (•) and crosses (x) show bonding in; (C = 2, 0 = 16, H = 1)     (2 marks)
      1. Water
        H20//H-1, O-2.4
        Bonding in water
      2. Carbon(IV) oxide
        CO2//C=2.4, O=2.6
        Chemical Bonding for Carbon dioxide
    2. Why is water a liquid at room temperature while carbon (IV) oxide is a gas at room temperature? (1 mark)
      • Water has stronger hydrogen bonds between its molecules unlike carbon(IV)oxide has weak van der waals forces.
  16. A gaseous compound consists of 86% carbon and 14% hydrogen by mass. At s.t.p, 3.2dm3 of the compound has a mass of 6g. (C = 12 H = 1 molar gas volume at s.t.p = 22.4dm3)
    1. Calculate its empirical formula   (1 mark)
       Elements   C   H 
       % Mass  86   14 
       RAM  12   1
       Moles  86/12 =7.166   14/1=14 
       


      Mole ratio
       7.166
       7.166
        1
        1
         14  
       7.166
       1.95
        2

      E.F =CH2
    2. Calculate its molecular formula      (2 marks)
      If 3.2dm3   → 6g
         22.4dm3 → ?
      22.4 × 6   =42 ✓1
           3.2
      MF=(EF)n
        n=R.M.M
             E.F.M
          =42/14=3 ✓½
      MF =(CH2)3
           =C3H ✓½
  17.  
    1. Identify the following cleansing agents.
      1. CH3(CH2)12CH2 -COO-Na+
        • Soapy detergent
      2. Cleansing agent
        • Soapless detergent
    2. Which cleansing agent is more suitable for washing in water containing magnesium sulphate.   (1 mark)
         Soapless detergent or Cleansing agent
    3. State one advantage of using the cleansing agent in (b) above.     (1 mark)
      • It does not pollute the environment as it is biodegradable.
      • Does not form scum with hard water.
  18. The structure below represents a segment of a polymer. Use it to answer the questions that follow.
             Structure representing segments of a monomer
    1. Draw the structure of the monomer.  (1 mark)
      Photo of structure of a monomer
    2. Given that the molecular mass of the polymer is 21000 find the value of n.  (2 marks)
      R.M.M of monomer =42
      n=21,000 =500
             42
  19. 50cm3 of oxygen gas diffused through a porous plug in 80 secs. How long will it take 100cm3 of sulphur (IV) oxide to diffuse through the same plug? (S = 32 0= 16)      (3 marks)
    If 50cm3 → 80sec
      100cm3→ ?
    100×80 =160sec
        50
    Sulphuric dioxide diffusing a plug
    160 √32
    TSO   √64
    TSO= 160 × 8
                      √32
              =226.27417sec
  20. When a current of 0.5 amperes was passed for 32 minutes and 10 seconds through fused chloride of metal P 0.44 of P was deposited. Determine the charge of the ion of metal P. (IF = 96,500C, P =88)       (3 marks)
    Q=IF
      =0.5×((32×60)+10)
      =0.5×1930
      =965c
    It 965c→0.44g
          ?   →88
    965×88=193,000c
       0.44
    If IF=96,500c
        ?=193,000c
    193,000 =2F
     96,500
    Thus the charge =2+
  21. When calcium carbonate was added to a solution of dry hydrogen chloride in methyl benzene there was no observable reaction. Explain.    (2 marks)
    • Hydrogen Chloride gas does not dissociate in methyl benzene solvent hence the solution formed does not react with the Calcium Carbonate, thus no observable reaction.
  22. Study the set up below and answer the questions that follow.
             Studying a set up
    1. Explain why it is important to heat the water before heating the magnesium ribbon.    (1 mark)
      • To generate steam so as to drive out all the air inside the apparatus
    2. Name gas P.       (1 mark)
      • Hydrogen gas
    3. Write a balanced equation for the reaction which takes place in the combustion tube.     (1 mark)
      Mg(s) +H2O(g)→MgO(s) + H2(g)
  23. The chief ore of aluminium is bauxite which mainly contains Al2O3.2H20. The ore is initially purified before aluminium is extracted electrolitically.
    1. Identify the main impurities associated with this ore.      (1 mark)
      • Iron(III)oxide / Fe2O3
      • Silicon(IV)oxide/ SiO2
    2. Sodium hydroxide solution is used in the purification process. State its role.     (1 mark)
      It reacts with acidic SiO2 and amphoteric Al2O3 so that Fe2O3 is removed as red mad
    3. Given an equation for the reaction that forms Aluminium oxide (Alumina) from aluminium hydroxide.
      (1 mark)
      2Al(OH)3(g) arrow Al2O3(s) + 3H2O(l)
                                 ∆                          
                        
  24. 3g of 257Lr whose half-life is 8 days, remains after undergoing radioactive decay for 32 days. Find the original amount of substance.         (2 marks)
    3g   8days   6g  8days  12g   8days  24g  8days   48g
    Original Mass=48g
  25. Study the flow chart below and answer the questions that follow.
             Studying a flow chart
    1. Identify solution P.    (1 mark)
      • Cu(NO3)2/Copper(II)nitrate
    2. Write a chemical equation to show how solid R is formed.     (1 mark)
      Cu(NO3)2(aq) + Na2CO3(aq) → CuCO3(s) +2NaNo3(aq)
    3. State the observation made in process II.      (1 mark)
      • A blue precipitate is formed which dissolves to a deep blue solution.
  26. If 25.0cm3 of 0.1 MH2S04 solution neutralized a solution containing 1.06g of sodium carbonate in 250cm3 of solution, calculate,
    1. The molarity of sodium carbonate solution (Na=23, 0=16,C=12)       (1½marks)
      Moles of Na2CO3
      R.F.M=106
      =1.06/106
      0.01moles
      If 0.01moles→250cm3
              ?         →1000cm3
      1000 × 0.01 =0.04M
           250
    2. Volume of sodium carbonate solution used.   (1½ marks)
      H2SO4 + Na2CO3→Na2SO4(aq) + CO2(g) + H2O(l)
      From the r.r of 1:1
      Moles of H2SO4 used=Moles of Na2CO3
      Moles of H2SO4 used 
           0.1Moles → 1000cm3
               ?        → 25cm3
            0.1×25 =0.0025moles
              1000
       If 0.04moles →1000cm3
        0.0025moles→  ?
      0.0025 × 1000
               0.04
          =62.5cm3

 

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