Chemistry Paper 2 Questions and Answers - Kapsabet Pre Mock Exams 2021/2022

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CHEMISTRY
PAPER 2:THEORY

INSTRUCTIONS TO CANDIDATES:

  • Write your name and index number in the spaces provided above.
  • Sign and write the date of examination in the spaces provided.
  • Answer all the questions in the spaces provided.
  • All working must be clearly shown where necessary.
  • Mathematical tables and electronic calculators may be used.
  • Candidates should answer the questions in English.

 

  1. The set-up below was used to prepare and collect gas X. During the experiment cleaned magnesium ribbon was strongly heated before heating the wet glass wool.
    KapPreM Chem p2q1
    1. Name gas X……………….………………………………………………..…………..……. (1 mark)
    2. Why is magnesium ribbon cleaned before it is used? (1 mark)
    3. State one observation that would be made in the reaction tube. (1 mark)
    4. Write the equation for the reaction in the reaction tube. (1 mark)
    5. State one industrial use of the solid product formed in the reaction tube. (1 mark)
    6. What precaution should be taken at the end of experiment? Explain. (2 marks)
    7. At the end of the experiment 96.0cm3 of gas X were collected at 10°C and 1 atmosphere pressure. ( molar gas volume = 22.4liters at s.t.p, T =273K at s.t.p, P = 1 atmosphere at s.t.p).
      1. Determine the volume gas X would occupy at s.t.p. (2 marks)
      2. Calculate the mass of magnesium ribbon used (Mg = 24) (1mark)
  2.             
    1. The diagram below shows how sulphur is extracted by the Frasch process.
      KapPreM Chem p2q2a
      Indicate with arrows (→ or ←) what enters or leaves the tube A, B and C in the diagram above. (3 marks)
    2. State two properties of sulphur that enable it to be extracted using the Frasch Process. (1 mark)
    3.          
      1. Hydrogen sulphide is prepared by the action of dilute acids on metal sulphides. Explain why the combination of dilute hydrochloric acid and lead sulphide cannot be used to prepare the gas. (2 marks)
      2. Hydrogen sulphide is normally collected over warm water but not over cold water. Explain. (1 mark)
      3. State one chemical test for hydrogen sulphide. (1 mark)
  3. Study the standard electrode potential for the half cells given below and answer the questions that follow. The letters do not represent the actual symbols of the elements.
      E θvolts
    N+(aq) + e- N(g)   -2.92
    J+(aq) + e- J(g)   +0.52
    K+(aq) + e- ½K(g)  0.00
    ½ G(g) + e- G-(aq)  +1.36
    M2+(g) + 2e- M(g)  -0.44

    1.          
      1. Identify the strongest oxidizing agent. Give reason for your answer. (2marks)
      2. Which two half cells would produce the highest potential difference when combined? (1mark)
      3. Explain whether the reaction represented below can take place. (2marks)
        M(g)+2N+(aq) M2+(aq) +2N(g)
    2. 100cm3 of 2M sulphuric acid was electrolyzed using the set up represented by the diagram below.
      KapPreM Chem p2q3b
      1. Write the equation for the reaction that produces gas “L”. (1mark)
      2. Describe how gas “K” can be identified. (2 marks)
      3. Explain the differences in:
        1. The volume of gases produced at the electrodes. (2 marks)
        2. Brightness of the bulb if 100cm3 of 2M ethanoic acid is used in place of sulphuric acid. (1mark)
    3. A solution of 1.0 M copper II sulphate was electrolyzed using carbon electrodes. A steady current of 2.5 A was passed through the solution for 15 minutes and the mass of copper deposited was determined. Given that 1 mole of copper requires 2 Faradays to be deposited. Calculate the mass of copper deposited after 15 minutes. (3 marks)
      (Cu = 63.5, IF = 96,500C)
  4.          
    1. At. 30oC, 54g of potassium nitrate were added to 100g of water to make a saturated solution.
      Define a saturated solution. (1mark)
    2. The table below gives the solubilities of potassium nitrate salt at different temperatures.
      Temperature(ºC) 10 20 30 39 45 55 60
       Solubility(g/100g of H2O) 19 31 44 60 72 98 120

      1. Plot the graph of the solubility of potassium nitrate (y-axis) against temperature. (3marks)
      2. Use your graph to
        1. Determine the solubility of potassium nitrate at 25ºC (1mark)
        2. Determine the mass of potassium nitrate that remained undissolved when 80g of potassium nitrate were added to 100cm3 of water and heated to 40oC. (2marks)
    3. Determine the molar concentration of potassium nitrate at 25oC (K = 39, N= 14,O=16, density of water = 1.0g/cm3) (3 marks)
    4. The table below gives the solubilities of potassium bromide and potassium sulphate at 0ºC and 40ºC.
      Substance   Solubility g/100g water at
       0ºC 40ºC
      Potassium bromide  55  75
      Potassium sulphate 10 12

      When an aqueous mixture containing 60g of potassium bromide and 7g of potassium sulphate in 100g of water at 40oC was cooled to 0oC some crystals were formed.
      1. Identify the crystals formed. (1 mark)
      2. Determine the mass of the crystals formed. (1 mark)
  5. The extraction of aluminum from it s ore takes place in two stages, purification stage and
    Electrolys is stage. The diagram below shows the set – up for the electrolysis stage.
    KapPreM Chem p2q5
    1.          
      1. write the formulae of the ore from which aluminium extracted. (1 mark)
      2. Name one impurity, which is removed at the purification stage. (1 mark)
    2.        
      1. write ionic equation at each of the following
        1. Anode
        2. Cathode
      2. The melting point aluminium oxide is 2015ºC, but electrolysis is carried out between 800ºC.
        1. Why is the electrolysis not carried out at 2015ºC (1 mark)
        2. What is done to lower the temperatures? (1 mark)
      3. The aluminium which is produced is tapped off as a liquid. What does this suggest about it smelting point? (1 mark)
  6. Study the table below and answer the questions that follow. The letters do not represent the actual symbols of the element.
    Formula of ion Electronic configuration
    E2+  2
    D-  2.8
    Cl- 2.8.8
    B3+ 2.8
    A2+ 2.8

    1. With a reason, select the elements found in:
      1. The same group (1½ marks)
      2. Period three (1½ marks)
      3. What is the name given to the group to which element E belongs? (1 mark)
    2. With a reason compare the atomic radius of elements B and A. (2 marks)
    3. State two industrial uses of element B. (2 marks)
    4. How does the reactivity of E and A compare? Explain your answer. (2 marks)
    5. Write the formula of the compound formed when D and A react together. (1 mark)
    6. What type of bond is formed when element E reacts with oxygen? Give a reason for your answer. (2 marks)
  7.        
    1. Describe a chemical test that can be used to distinguish CH3COOH from CH3CH2OH (3 marks)
    2. Draw and name one isomer of the third member of the homologous series CnH2n-2. (1 mark)
    3. Propan-1-ol was subjected to a series of experiments.
      1. It was heated with concentrated sulphuric (VI) acid at temperature of 160-180ºC to form gas R in the process called W. Gas R was then subjected to high pressure to form a polymer X.
        1. Name gas R. (1mark)
        2. What is the name given to process W? (1mark)
        3. State one disadvantage of continued use of polymer X. (1mark)
      2. Propan-1-ol was converted to propanoic acid in the process Y. The propanoic acid was then reacted with dilute sodium hydroxide solution to form solution C which was heated to saturation and cooled. Crystals of C were obtained. Solid C was added to soda lime and the mixture heated. Ethane gas was collected.
        1. Name the process Y. (1mark)
        2. Write the equation for the reaction that occurs when solid C is heated with sodalime. (1mark)
    4. In the presence of U.V light, ethane gas undergoes substitution reaction with chlorine.
      1. What is meant by the term substitution reaction? (1 mark)
      2. Give the structural formula and the name of the organic compound formed when equal volumes of ethane and chlorine react together. (1 mark)

MARKING SCHEME

  1.       
    1. Hydrogen gas
    2. Remove oxide layer
    3. Bright white flame of burning magnesium
      White solid residue of magnesium oxide
    4. Mg(s) + H2O(g) â†’ MgO(s) + H2(s) 
      No marks for: Missing symbols, unbalanced equation
    5. Manufacture of cements
      Antacid
      Linings of furnaces
    6. Heating should be continued - to prevent water from sucking back
    7.      
      1. T1=283 , T2= 273
      2. P1=1, P2=1
        V1=96, V2=?
        P₁V₁= P₂V₂
         T₁       T₂
        1 x 96 1 x X
          283         273
        x =96 x 273
                 283
        =96.600cm3
      3. Moles of H2
        22.4litres = 1 mole
        0.096 = 0.096 x 1/22.4= 0.00429
        Mole ratio 1:1
        Mass= 0.00429 x 24
        = 0.10296g
  2.               
    1.    
      qa2a      
    2. Insoluble in water
      Low Boiling point
    3.        
      1. Formation of insoluble lead chloride which forms a coating on the acid thus prevents further reaction
      2. Insoluble in warm water
      3. Bubble the gas in lead nitrate , reacting with lead acetate thus black precipitate is formed.
  3.         
    1.           
      1. G- most positive electrical potential
      2. G and N half cell.
      3. -NO is more reactive and can't displace.
    2.             
      1. 4OH-(aq) → 2H2O(l) + O2(g) + 4e
      2. Produce a "pop" sound when burning splint is inserted inside.
      3.         
        1. Ratio of electrons required to produce the gas is 4:2, 2:1
        2. In 2M ethanoic the bulb would be less bright- ethanoic acid is weaker acid and dissociates partially to produce less ions
    3. Mass = 2.5 x 15 x 60 x 63.5
                         2 x 96500
      = 0.7402g
  4.            
    1. A solution that can't dissolve any more solute at a given temperature
    2.       
      1.    
        KapPreM Chem p2qa4bi
      2.       
        1. 38g/100g of water ±2
        2. At 40ºC - 62g/100g of water
           80 -62
          <ass undissolved = 18g
    3. 38g in 100cm3 of water
      KNO3 = 39 + 14 + 48 
      Moles = 38/101
      = 0.3762 moles
      0.3762 moles = 100cm3
      1000 x 0.3762 = 1000cm3
            100
      =3.76M
    4.        
      1. Potassium Bromide
      2. 60-55= 5g
  5.                        
    1.       
      1. Al2O3.H2O
      2. Iron III oxide , silica
    2.          
      1.      
        1. 2O2- â†’ O2 + 4e
          also accept :
          6O2- â†’ 3O2 + 12e

        2. 3Al3+ + 3e â†’ Al
          also accept
          4Al3+ + 12e â†’ 4Al
      2.          
        1. To save on cost of production by swrving electricity
        2. Cryolite is added as an impurity to lower melting point
        3. Melting point of Al is higher than Boiling POint
  6.        
    Formula of ion   Electronic configuration
    E2+ 2.2  2
    D- 2.7  2.8
    Cl- 2.8.7 2.8.8
    B3+ 2.8.3 2.8
    A2+ 2.8.2 2.8

    1.        
      1. E,A each 1/2 or D and Cl
      2. Cl, B , A each 1/2
      3. Alkaline earth metal
    2. A has a larger radius . More protons hence stronger nuclear charge
    3. Aeroplane bodies
      Electrical cables
    4. A is more reactive - A is more electropositive due to a larger radius.
    5. AD2
    6. Ionic - involves transfer of electrons from E oxygen (accept metal and non-metal)
  7.        
    1. Add Na2CO3 or NaHCO3 - In CH3COOH effrevesence while in CH3CH2OH , no effrevesence
      or
      Accept any reaction with oxidising agent   
    2. n=4 
      C4H6
      Chem qa7b
      but- 1- yne
      But -2- yne 
      Chem qa7bii
    3.                
      1.              
        1. Steam/ water
        2. Dehydration
        3. Pollutes the environment
      2.          
        1. Oxidation
        2. CH3CH2COONa + NaOH â†’ Na2CO3 + C2H6( ignore symbols)
    4.            
      1. Reaction where one or more atoms of an alkane is replaced by halogen
      2. Chloroethane
        Chem qa7dii

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