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

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.
            
   
   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
            
   
   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.
             
    
    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
             
    
    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
    
    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.
             
    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.
    
    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.
            
   
   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
      2H₂O_2(l)  2H₂O_(l) +O_2(g)   //    2H₂O_2(l) →  2H₂O_(l) +O_2(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
            
   
   1. Write an equation for the formation of gas K [1 mk]
      Ca_(s) +2H₂O_(l) → Ca(OH)_2(aq) + H_2(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]
   
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) + H₂SO_4(aq) → Na₂SO_4(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.
             
    
    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⁺Cl⁻_2(aq) + CO_2(g) +H₂0_(l)
    2H⁺_(aq) + CO²⁻_3(s) → CO_2(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]
       
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]
       
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
    Na₂CO_3(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.
             
    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) + O_2(g) → Na₂O_2(g)
    2. Reaction between Nitric Acid and Copper Carbonate [1mk]
       2HNO_3(aq) + CuCO_3(s) → CuNO_3(aq) +CO_2(g) + H₂O_(l)
    3. Reaction between Zinc and hydrochloric acid [1mk]
       Zn_(s) + 2HCl_(aq) → ZnCl_2(aq) + H_2(g)
    4. Heated Silver nitrate reaction [1mk]
       2AgNO_3(s)   2Ag_(s) + 2NO_2(g) + O_2(g)
23. The diagram shows PH values for 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.