Chemistry Paper 1 Questions and Answers - Form 3 Mid Term 1 Exams 2021

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  1. Name another gas which is used with oxygen in welding [1 Mk]
  2.  
    1. write the electronic configuration of calcium (atomic number 20) and magnesium (atomic number 12)
      Calcium   [½ Mk]
      Magnesium     [½ Mk]
    2. Why is calcium more reactive than magnesium? [2 Mks]
  3. The table below shows the relative atomic masses and the percentage abundance of the isotopes T1 and T2 of element T
       RAM   % abundance 
     T1   62.93   69.09
     T2  64.93  30.91
    Calculate the relative atomic mass of element T [3 mks]
  4. The diagram below is a set-up for the laboratory preparation of oxygen gas.
             lab prep for oxygen
    1. Name solid P.       [1 mk]
    2. Write an equation for the reaction that takes place in the conical flask      [1 mk]
    3. Give two commercial uses of oxygen [2 mks]
  5. State two reasons why hydrogen is not commonly used as a fuel [2 mks]
  6. The figure shows a set-up by a form three student to prepare a certain gas
             figure showing set up for certain gas
    1. Write an equation for the formation of gas K [1 mk]
    2. Give one use of gas K in the industries [1 mk]
    3. Give one use of the resulting solution after the metal has reacted [1 mk]
  7. Draw a dot and cross diagram showing the bonding in a molecule of calcium oxide. Name the type of bond. [3 mks]
  8. When 0.288g of an oxide of metal M was reduced using suitable reducing agent, 0.256 of pure metal was formed. Determine the empirical formula of the oxide of the metal M. [M=64 O=16]   [4 mks]
  9. X+ is an ion with electronic configuration 2,8,8. Identify element X [1 mk]
  10. 20g of solid sodium hydroxide were dissolved in distilled water and made to 400cm3. 30cm3 of this solution required 27cm3 of dilute sulphuric (iv) acid for complete reaction. [Na=23 O=16 H=1]
    Determine
    1. Moles of sodium hydroxide contained in 30cm3 of solution [2 mks]
    2. Moles of sulphuric (iv) acid that reacted [2 mks]
    3. Concentration of the sulphuric (iv) acid in moles per litre [2 mks]
  11. The diagram shows the structures of two allotropes of carbon. Study them and answer the questions that follow.
             diagram of structures of two allotropes of carbon
    1. Name allotrope A and B [2 mks]
    2. Give two uses of allotrope B [2 mks]
    3. Which allotrope conducts electricity? Explain. [2 mks]
  12. An oxide of element F has the formulaF2O5
    1. Determine the oxidation state of F. [1 mk]
    2. In which group of the periodic table is element F? [1 mk]
  13. Explain how you would obtain solid sodium carbonate from a mixture of lead II carbonate and sodium carbonate. [3 mks]
  14. Give two properties of aluminum that makes it very suitable for making cooking utensils [2 mks]
  15. Write down an ionic equation for the reaction between dilute hydrochloric acid and calcium carbonate [3 mks]
  16. The diagram shows electric current passing through dilute sulphuric (iv)acid
             diagram on electric current passing through H2SO4
    1. On the diagram identify the cathode and the anode [2 mks]
    2. Identify substances X and Y [2 mks]
  17. State and explain the change in mass that occur when following substances are separately heated in open crucibles [4 mks]
    1. Copper metal
    2. Copper II nitrate
  18. The diagram below represents a paper chromatograph for three brands of juices suspected to contain banned food colourings
    diagram on paper chromatography
    The result showed presence of banned food colourings in L and M only
    1. On the diagram
      1. Circle the spots which show the banned colourings [2 mks]
      2. Show the solvent front [1 mk]
    2. On the same diagram indicate and label the baseline [1 mk]
  19. Determine the number of sodium ions contained in 25cm3 of 0.5M sodium carbonate solution [a=6.023 x 1023]      [3 mks]
  20. The graph below shows a curve obtained when water at 20℃ was heated for 15 mins.
             graph showing a curve when water is heated
    1. What happens to the water molecules between points W and X [1 mk]
    2. In which part of the curve does a change of state occur? [1 mk]
    3. Explain why the temperature does not rise between points X and Y [1 mk]
  21. Write down the formula of the following compounds
    1. Potassium manganate VII       [1mk]
    2. Aluminium oxide          [1mk]
    3. Iron III chloride        [1mk]
  22. Write balanced equations for the following reactions
    1. Reaction between sodium and excess oxygen [1mk]
    2. Reaction between Nitric Acid and Copper Carbonate [1mk]
    3. Reaction between Zinc and hydrochloric acid [1mk]
    4. Heated Silver nitrate reaction [1mk]
  23. The diagram shows PH values for several substances.
    diagram on PH values of several substances
    Choose the likely PH value for,
    1. Dilute Hydrochloric acid      [1mk]
    2. Calcium hydroxide          [1mk]
    3. Sodium hydroxide        [1mk]
    4. Lemon juice               [1mk]
  24. Briefly outline how you would obtain ethanol from a mixture of ethanol and water. [3mks]
  25.  
    1. What is rust? [1mk]
    2. Give two advantages of rusting.

Marking Scheme

  1. Name another gas which is used with oxygen in welding [1 Mk]
    • Hydrogen/Acetylene or Ethyne  
  2.  
    1. write the electronic configuration of calcium (atomic number 20) and magnesium (atomic number 12)
      Calcium   [½ Mk] 
      2, 8, 8, 2 
      Magnesium     [½ Mk]
      2, 8, 2  
    2. Why is calcium more reactive than magnesium? [2 Mks]
      • The two valency electrons of calcium are further away from the nucleus, therefore not strongly held hence readily lost/donated
  3. The table below shows the relative atomic masses and the percentage abundance of the isotopes T1 and T2 of element T
       RAM   % abundance 
     T1   62.93   69.09
     T2  64.93  30.91
    Calculate the relative atomic mass of element T [3 mks]
    R.A.M = 62.93 × 69.09 + 64.93 × 30.91
                         100                   100
             = 4347.8337 + 2006.9863
                               100
             = 6354.82
                   100
             = 63.55
  4. The diagram below is a set-up for the laboratory preparation of oxygen gas.
             lab prep for oxygen
    1. Name solid P.       [1 mk]
      • Manganese IV Oxide
    2. Write an equation for the reaction that takes place in the conical flask      [1 mk]
                      MNO2
      2H2O2(l) arrow2H2O(l) +O2(g)   //    2H2O2(l) →  2H2O(l) +O2(g)
    3. Give two commercial uses of oxygen [2 mks]
      • Welding
      • Rocket fuel
      • Hospital, ICU
      • Steel making
      • Deep sea diving
  5. State two reasons why hydrogen is not commonly used as a fuel [2 mks]
    • Expensive to produce
    • Explosive
  6. The figure shows a set-up by a form three student to prepare a certain gas
             figure showing set up for certain gas
    1. Write an equation for the formation of gas K [1 mk]
      Ca(s) +2H2O(l) → Ca(OH)2(aq) + H2(g)
    2. Give one use of gas K in the industries [1 mk]
      • Welding
      • Manufacture of HCL acid
      • Hardening of vegetable oil into margarine
      • Manufacture of Ammonia gas
    3. Give one use of the resulting solution after the metal has reacted [1 mk]
      • Test for Carbon IV oxide
  7. Draw a dot and cross diagram showing the bonding in a molecule of calcium oxide. Name the type of bond. [3 mks]
    Bonding in calcium oxide molecule
  8. When 0.288g of an oxide of metal M was reduced using suitable reducing agent, 0.256 of pure metal was formed. Determine the empirical formula of the oxide of the metal M. [M=64 O=16]   [4 mks]
    Element      M          O
    Mass        0.256     0.032
    RAM            64        16
    Moles       0.256    0.032
                     64         16  
                    0.004    0.002
    Ratio of    0.004     0.002
    moles       0.002     0.002
                       2            1
    Empirical Formula = M2O
  9. X+ is an ion with electronic configuration 2,8,8. Identify element X [1 mk]
    • Potassium
  10. 20g of solid sodium hydroxide were dissolved in distilled water and made to 400cm3. 30cm3 of this solution required 27cm3 of dilute sulphuric (iv) acid for complete reaction. [Na=23 O=16 H=1]
    Determine
    1. Moles of sodium hydroxide contained in 30cm3 of solution [2 mks]
      Molar mass of NaOH= 40g
      20/40 = 0.5M
      0.5 = 400cm3 
        ? = 1000cm3
      0.5 × 1000
          400
      =1.25M
      1.25 = 1000cm3 
        ?    =30cm3 
       1.25 × 30
            1000
      =0.0375moles
    2. Moles of sulphuric (iv) acid that reacted [2 mks]
      2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l)
      Mol of H2SO4 = Mol NaOH Mole ration in equation above is 1:2
                                  2 
                          =0.0375
                                2
      Mol of H2SO4 =0.01875moles
    3. Concentration of the sulphuric (iv) acid in moles per litre [2 mks]
      0.01875 = 27cm3
         ?        =1000cm3
      1000 × 0.01875 
              27
      =0.6944M
  11. The diagram shows the structures of two allotropes of carbon. Study them and answer the questions that follow.
             diagram of structures of two allotropes of carbon
    1. Name allotrope A and B [2 mks]
      • A-Graphite
      • B-Diamond
    2. Give two uses of allotrope B [2 mks]
      • Tips of drills
      • Jewellery 
      • Glass cutter
      • Making bearing
      • Padlocks
    3. Which allotrope conducts electricity? Explain. [2 mks]
      • A/Graphite-The fourth electron of each carbon is unbounded hence free to conduct electricity
  12. An oxide of element F has the formula F2O5
    1. Determine the oxidation state of F. [1 mk]
      F2O5 = O
      2F + 5(−2) = 0
      2F+−10=0
      2F = 0+10
      2         2 
      F= +5  
    2. In which group of the periodic table is element F? [1 mk]
      • Group V
  13. Explain how you would obtain solid sodium carbonate from a mixture of lead II carbonate and sodium carbonate. [3 mks]
    • Put the mixture in water and stir. Sodium carbonate dissolves while lead carbonate does not. Filter to remove lead carbonate as a residue. Evaporate the filtrate to saturation and allow to cool for crystallization of sodium carbonate to take place
  14. Give two properties of aluminum that makes it very suitable for making cooking utensils [2 mks]
    • Good thermal conductivity.
    • malleability.
    • light weight
    • high melting point 
  15. Write down an ionic equation for the reaction between dilute hydrochloric acid and calcium carbonate [3 mks]
    2H+Cl(aq)+ Ca2+CO2−3(s) → Ca2+Cl2(aq) + CO2(g) +H20(l)
    2H+(aq) + CO2−3(s) → CO2(g) +H2O(l)
  16. The diagram shows electric current passing through dilute sulphuric (iv)acid       
    1. On the diagram identify the cathode and the anode [2 mks]
    2. Identify substances X and Y [2 mks]
      answer to electrical current passing through H2SO4
  17. State and explain the change in mass that occur when following substances are separately heated in open crucibles [4 mks]
    1. Copper metal
      • Mass increase-Copper metals combines with oxygen forming copper oxide
    2. Copper II nitrate
      • Mass reduction-Copper II Nitrate is decomposed by heat forming copper oxide, Nitrogen IV Oxide and oxygen gases, the gases escape.
  18. The diagram below represents a paper chromatograph for three brands of juices suspected to contain banned food colourings
    The result showed presence of banned food colourings in L and M only
    1. On the diagram
      1. Circle the spots which show the banned colourings [2 mks]
      2. Show the solvent front [1 mk]
    2. On the same diagram indicate and label the baseline [1 mk]
      answer on paper chromatograph
  19. Determine the number of sodium ions contained in 25cm3 of 0.5M sodium carbonate solution [a=6.023 x 1023]      [3 mks]
    Moles of Na2CO3 25   × 0.5
                                    1000
                               =0.0125
    Na2CO3(aq) → 2Na+(aq) + CO2−3(aq) 
    Moles of Na+ = 2 x 0.0125
                        = 0.025
    Number of Na+ = 0.025 x 6.023 x 1023
                           = 1.5058 x 1022
  20. The graph below shows a curve obtained when water at 20℃ was heated for 15 mins.
             graph showing a curve when water is heated
    1. What happens to the water molecules between points W and X [1 mk]
      • Water molecules gain energy and move faster
    2. In which part of the curve does a change of state occur? [1 mk]
      • XY
    3. Explain why the temperature does not rise between points X and Y [1 mk]
      • Supplied energy is used to break bonds between water molecules in liquid state and become free molecules in gaseous state
  21. Write down the formula of the following compounds
    1. Potassium manganate VII      [1mk]
      KMnO4
    2. Aluminium oxide          [1mk]
      Al2O3
    3. Iron III chloride        [1mk]
      FeCl3
  22. Write balanced equations for the following reactions
    1. Reaction between sodium and excess oxygen [1mk]
      2Na(s) + O2(g) → Na2O2(g)
    2. Reaction between Nitric Acid and Copper Carbonate [1mk]
      2HNO3(aq) + CuCO3(s) → CuNO3(aq) +CO2(g) + H2O(l)
    3. Reaction between Zinc and hydrochloric acid [1mk]
      Zn(s) + 2HCl(aq) → ZnCl2(aq) + H2(g)
    4. Heated Silver nitrate reaction [1mk]
      2AgNO3(s) heat arrow 2Ag(s) + 2NO2(g) + O2(g)
  23. The diagram shows PH values for several substances.
    diagram on PH values of several substances
    Choose the likely PH value for,
    1. Dilute Hydrochloric acid      [1mk]
      • 2
    2. Calcium hydroxide          [1mk]
      • 9
    3. Sodium hydroxide        [1mk]
      • 13
    4. Lemon juice               [1mk]
      • 5
  24. Briefly outline how you would obtain ethanol from a mixture of ethanol and water. [3mks]
    • Heat the mixture in a fractional distillation apparatus maintaining the temperature at the boiling point of ethanol which is lower than that of water. Ethanol will distill over, leaving water behind.
  25.  
    1. What is rust? [1mk]
      • Hydrated Iron III oxide
    2. Give two advantages of rusting.
      • Enable paint to stick properly on steel articles
      • Assist the environment to get rid of scrap metal objects.

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Read 774 times Last modified on Wednesday, 04 August 2021 12:27

1 comment

  • Comment Link wasonga emmanuel Sunday, 05 September 2021 18:13 posted by wasonga emmanuel

    thanks

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