Chemistry Paper 1 Questions and Answers - Form 4 End Term 1 Exams 2022

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Questions

  1. The set-up below was used to investigate the effect of steam on copper turnings.
    ChemForm4ET122p1q1
    1. What was observed in the boiling tube? Explain (2mks)
    2. Suggest one other metal that would behave as copper turnings in the above set up if used. (1mk)
  2.      
    1. State Graham’s law of diffusion. (1 mk)
    2. A certain volume of gas S takes 180 seconds to diffuse through a porous plug. Molar mass of S is 18. Equal volume of gas Q takes 240 seconds to diffuse through the same plug.
      Calculate the molar mass of Q. (2mks)
  3. A student set-up the apparatus shown below attempting to collect oxygen gas.
    ChemForm4ET122p1q3
    1. State one mistake the student made. (1 mk)
    2. Identify liquid Q. (1 mk)
    3. What property enables the gas to be collected as shown above? (l mk)
  4. Sodium chloride is accidentally mixed with lead( II) sulphate. Explain how sodium chloride crystals can be obtained from the mixture. (3mks)
  5. The molecular formula of a hydrocarbon is C11H24,
    The hydrocarbon can be converted into other hydrocarbons as shown below.|
    ChemForm4ET122p1q5
    1. Name process R ………………………………………………………………… (½ mk)
    2. Draw the structural formula of Y and give its name. (1 ½ mks)
  6. The third number of the alkenes is converted to its corresponding saturated hydrocarbon by hydrogenation. Using the bong energy values given below, answer the questions that follow.
    Bond           Bond energy kJ/Mol
    H-H               432
    C=C              610
    C-C               346
    C-H               413
    Determine the enthalpy change for the conversion of the third member of the alkenes to its corresponding saturated hydrocarbon by hydrogenation. (3mks)
  7. Use the information in the energy cycle below to answer the questions that follow.
    ChemForm4ET122p1q7
    1. What is the name given to the energy changes? (3mks)
      H1. ………………………………………………………………………….
      H2. ………………………………………………………………………….
      H3. …………………………………………………………………………
    2. Given that ∆ H1= 2237KJ/Mol and ∆H2=-2378KJ/Mol, calculate the value of ∆H3. (l mk)
  8. When solid Zinc carbonate was added to a solution of hydrogen chloride in methylbenzene, there was no observable change. On addition of some water to the mixture there was effervescence. Explain these observations. (2mks)
  9. Study the chart below and answer the questions that follow.
    ChemForm4ET122p1q9
    1. Name:
      1. Cations present in mixture X. (1mk)
      2. Anions present in the solution. (1mk)
    2. Write an equation to show how the white precipitate in step III dissolves. (1mk)
    3. Name the process outlined in step IV above. (1mk)
  10. An element X has two naturally occurring isotopes 22 X1 and 20 X2. If its relative atomic mass is 21.8, calculate the percentage abundance of the more stable isotope. (2mks)
  11. State two conditions that would make the boiling point of water to be higher than 100oC. (2 marks)
  12. Study the following equilibrium equation.
    2X2(g) + Y2(g) ⇌ 2X2Y(g) ∆H = -197kJ/mol
    1. Suggest two ways of increasing the yield of X2Y. (1 mark)
    2. Draw the energy level diagram for the forward reaction. (2 marks)
  13. 5.0g of calcium carbonate were allowed to react with 25cm3 of 1.0M hydrochloric acid until there was no further reaction. Calculate the mass of calcium carbonate that remained unreacted. (3 marks) (Ca = 40, C = 12, O = 16)
  14. A student fetched water from a river in a limestone area. He used it for washing and realized that it did not lather easily.
    1. Name the two ions that prevent lathering. (1 mark)
    2. Given that the structure of soap is C17H35COONa.
      Explain by means of ionic equations how the above ions prevent lathering. (2 marks)
  15. M grams of a radioactive isotope decayed to 5 grams in100 days. The half-life of the isotope is 25 days.
    1. What is meant by half life? (1 Mark)
    2. Calculate the initial mass M of the radioactive isotope. (2 Marks)
  16. 20cm³ of a dibasic acid required 25cm³ of 0.1M NaOH for complete neutralization.
    1. How many moles of sodium hydroxide reacted with the dibasic acid? (1 mark)
    2. Calculate the concentration of the dibasic acid in moles per litre. (2 marks)
  17. When 25cm³ of 0.5M HCl is added to 25cm³ of 0.5M NaOH the temperature of the solution rose from 23 ®C to 26 ®C. Given that the density of the solution is 1gcmˉ³ and its specific heat capacity is 4.2Jgˉ¹Kˉ¹.
    1. Determine the amount f heat evolved that caused the temperature rise. (1 mark)
    2. Work out the molar enthalpy of neutralization for this reaction. (2 marks)
  18. The figure below shows a burning splint that was put across the middle of a non-luminous flame. Explain the results. (2 marks)
    ChemForm4ET122p1q18
  19. 3.22g of hydrated sodium sulphate, Na2SO4.XH2O were heated to a constant mass of 1.42g. Determine the value of X in the formula. (Na = 23.0, S = 32.0, O = 16.0, H = 1). (3 marks)
  20. The following chromatogram was obtained in an experiment to investigate the components present in certain dyes.
    ChemForm4ET122p1q20
    1. Which two dyes when mixed would produce A? (1 mark)
    2. Which dye is pure? (1 mark)
    3. Indicate on the diagram the solvent front. (1 mark)
  21. The following are electrode potentials of the half cells.
    Half-cell               E® volts
    M2+(aq)/M(s)       -0.76
    C2+(aq)/C(s)       +0.34
    1. Calculate the potential difference of the following cell. (1 mark)
      M(s)/M2+(aq) //C2+(aq) /C(s)
    2. Draw an electrochemical cell for the cells in (a) above. (3 marks)
    3. Show the electrode which represents the anode. (1 mark)
  22. The diagram below shows the reaction of zinc granules with hydrochloric acid.
    On the diagram sketch the graph that would be obtained if zinc powder of same quantity was used and label it C2. Explain. (2 marks)
    ChemForm4ET122p1q22
  23. A copper spoon was coated with silver metal as shown below.
    ChemForm4ET122p1q23
    1. Write an equation for the reaction that occurs at the copper spoon cathode. (1 mark)
    2. How many grams of silver would be deposited on the spoon in two hours using steady current of 0.03A? (1 F = 96500C, Ag = 108.0) (3 marks)
  24. Copper (II) sulphate solution was electrolyzed using graphite electrodes.
    1. State the observations made at the electrodes. (2marks)
      Anode
      Cathode
    2. Write the equation for the anode reaction. (1mark)
  25. Write down a balanced equation to show the effect of heat on each of the following substances.
    1. Anhydrous copper (II) sulphate (1mark)
    2. Potassium nitrate salt (1mark)
    3. Silver nitrate (1mark)
  26. A compound with the formula X (OH)3(not its actual chemical formula) reacts as shown below
    X(OH)3(s) + OH-(aq) → X(OH)4(aq)
    X(OH)3(s) + 3 H+(aq) → X3+(aq) + 3H2O(l)
    1. State the name of compounds that behave like X (OH)3 in the two reactions above. (1mark)
    2. Name two elements whose hydroxides behave like that of X. (2marks)
  27. Chlorine water was exposed to sunlight for one day using the set up below.
    ChemForm4ET122p1q27
    After one day a gas was collected
    1. Identify the gas that was collected. (1mark)
    2. State the observations made in the liquid. (2mark)
    3. What will happen to the pH of the solution after one day? (1mark)

Marking Scheme

  1.               
    1. No observable change. Copper remains brown. Copper is below hydrogen in the reactivity series hence cannot display hydrogen from steam.
    2. Gold, Steam, mercury, platinum
  2.   
    1. Under the same conditions of temperature and pressure the rate of diffusion of a gas is inversely proportional to the square root of its density.
    2.        
      ChemForm4ET122p1qa2b
  3.              
    1. Thistle funnel should dip into solutions in the flask.
    2. Hydrigen peroxide
    3. Slightly soluble in water.
  4. Add water to the mixture ¼ and stir to dissolve sodium chloride.
    Filter off the lead II sulphate residue. Heat the filtrate to dryness to obtain sodium chloride crystals.
  5.          
    1.  Cracking
    2. Ethene
      ChemForm4ET122p1qa5b
  6.      
    ChemForm4ET122p1qa6
    ΔH(2 x 346) + 610 + 8xx413 + 432) - (10xx413 + 3 x 346) 
    = 5038 - 5168
    -130kj/mol-1

  7.            
    1.     
      H1 - Lattice energy
      H2 - Hydration energy

    2. 2237+(-2378)
      = -141KJmol-1

  8. Hydrogen chloride in methyl benzene is in molecular form. It allows no reaction with Zinc carbonate. When water is added, the hydrogen chloride ionizes and the H ions react with Zinc carbonate producing carbon(IV)oxide.
  9.          
    1.       
      1. Cu2+ and Za2+
      2. SO2-4

    2. Zn(OH)2(s) + 4NH3(aq) → Zn(NH3)42+(aq) + 2OH(aq)

    3. Neutralization

  10. Let y be % abundance of most abundant.
    22y + (100-x)20 =  218
            100
    Y= 90%

  11.    
    • Presence of impurities
    • At an altitude above sea-level//pressure above 1 atm(760mmHg)
  12.              
    1.       
      • Lowering the temperature
      • Increasing pressure.
    2.       
      ChemForm4ET122p1qa12b

  13. CaCO3(s)+ 2HCP(aq) → CaCl2(aq) + CO2(g) + H2O(l)
    1 mole - 1000cm3
    xmol - 25cm3
    = 0.025 moles
    0.025  = 0.0125
     2
    0.0125 moles = 5x/100
    = 1.25
    5 - 1.25
    = 3.75g

  14.        
    1. Magnesium ions
      Calcium ions
    2. Ca2+(aq) + C17H15COO-(aq) → C17H35COOCa(s)
      Mg2+(aq) + C17H35COO-(aq) → C17H35COOMg(aq)
  15.           
    1. Time taken for given mass of a radioactive isotope to reduce to half its original mass.
    2. 100/25 = 4 half lifes
      5 - 10 - 20 - 40 - 80=80g
  16.           
    1. 2NaOH(aq) + H2x(aq) → Na2X(aq) + H2O(l)
      25cm3             20cm3
      0.1M
      0.1moles - 1000cm3
      x moles - 25cm3
      x= 0.0125 = 0.0025 moles
          1000
           
    2. 0.0025 = 0.00125 moles
         2
      0.00125 moles - 20cm3
      x  - moles = 1000cm3
      x = 0.00125 x 100
                 20
      = 0.0625M

  17.               
    1. ΔH= MCΔT
      = 0.05 x 4.2 x 3
      = 0.63kg

  18. The middle part was not burnt because it was int he region of unburnt gases
    The ends were burnt because of complete combustion of the gas at the ends which were hot.

  19. Na2SO4.X H2O → NaSO4(aq) + XH2O(l)
        3.22g
    mass 1.42g 1.8
    RAM   119  18
    Moles 1.42 - 0.011
    119
    1.8 = 0.1
    18
    DSR  0.011 = 1
    0.011
      0.1    = 10
    0.011
    MR 1  10
  20.       
    1. C and D
    2. B   
       
  21.             
    1. Eθ = Ereduction - E oxidation
      =(0.34) - (-0.76)
      = +1.1V

    2.     
      ChemForm4ET122p1qa21b

    3. Electrode C

  22. Powder has large surface area in contact with the acid.
  23.           
    1. Ag+(aq) + e- → Ag(s)

    2. Q= it
      = 0.03 x 2 x60 x 60 = 216C
      96500C - 108g
      216C - xg
      x = 216 x 108
             96500
      = 0.242g
  24.            
    1. Anode : pale blue colour of CuSO4 fades 
      Cathode:  Red brown deposits of copper metal

    2.    4OH-(aq) → 2H2O(l) + O2(g) + 4e-

  25.                
    1. CuSO4(s) → CuO(s) + SO3(g)
    2. 2KNO3(s) → 2KNO2(s) + O2(g)
    3. AgNO3(s) → 2Ag(s) + 2NO2(g) + O2(g)

  26.           
    1. Amphoteric hydroxides

    2. lead(II) hydroxide
      Aluminium hydroxide
      Zinc (II)hydroxide
  27.             
    1. Oxygen gas
    2. The yellow colour of the sdolution fades.
    3. The pH since the weak acid(HOCl) is being converted into strong acid (HCl)

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