Chemistry Paper 2 Questions and Answers - Mang'u Mock 2020 Exam

CHEMISTRY
PAPER 2
TIME: 2 HOURS.

Instructions to candidates

• Answer ALL the questions in the spaces provided.

1.    
   1. An element S has an atomic number of 38 and belongs to period 5.
      1. What name is given to the group to which the element belongs? (1mk)
      2. Write the electronic configuration of the element (1mk)
   2. The table below gives information about some ions of certain elements. Study it and answer the questions that follow.
      

      Ion	Ionic Configuration	Ionic Radius (nm)	Atomic radii (nm)
      Q2-	2:8	0.136	0.072
      T3+	2:8	0.050	0.143
      W+	2:8	0.095	0.186
      X+	2	0.066	0.152

      
      
      1. Name the nature of the oxide formed when T³⁺ forms an oxide (1mk)
      2. Identify the ion of the most electronegative element (1mk)
      3. Compare the reactivity of elements forming ions W⁺ and X⁺ (1mk)
      4.    
         1. Draw a 'dot' and 'cross' diagram illustrating on the compound formed when T³⁺ combines with Q^2- (1mk)
         2. Name the type of structure formed (1mk)
            
            
      5. Name the charge carries would be present in:
         1. Chloride formed by W⁺ (1mk)
         2. Element of X⁺ (1mk)
   3. Two elements R and S belong to group VII of the periodic table with atomic numbers 17 and 53 respectively.
      1. State the electronic configuration of the ion R (1mk)
      2. S is a solid while R is a gas. Explain (1mk)
2.    
   1. If chlorine gas is passed over heated iron fillings and the product dissolved in water, a yellow solution is formed.
      1. What would be observed if aqueous ammonia is added to the yellow solution (1mk)
      2. Write the ionic equation for the reaction above in (i) (1mk)
   2. Study the reaction scheme below and answer the questions that follow.
      
      1. Write the ionic equations for the formation of
         1. Colourless solution X (1mk)
         2. Yellow precipitate (1mk)
      2. What observations are made when white precipitate S is heated strongly (1mk)
      3. Hydrogen sulphide gas was passed through colourless solution R. Write the equation for the reactions that took place (1mk)
   3.    
      1. A student was required to prepare a sample of copper metal using crystals of copper II sulphate and iron fillings. Describe how the student would obtain copper metal (3mks)
      2. The solution obtained in (i) above was electrolysed using inert electrodes.
         1. Name the product at cathode. (1mk)
         2. Calculate the mass of the product formed at the anode if a current of 0.15A was passed for 1 hour 5 seconds at s.t.p. (molar gas volume - 22.4cm³) (Fe=56, O=16, S=32, CU=63.5) (3mks)
3. The table below gives reduction potentials obtained when half cells for the following metals; J, K, L, M and N were connected to a copper half cell as reference electrode.
   

   metals	reduction potentials (volts)
   J-	-1.10
   K	-0.47
   L	0.00
   M	+0.45
   N	+1.16

   
   
   1.    
      1. What is metal L likely to be (1mk)
         Give a reason (1mk)
      2. Which metal cannot be displaced from its salt by any other metal in the table (1mk)
   2. If metal Kand M were used as electrodes to form an electrochemical cell
      1. Draw a well labeled diagram of this cell and the direction of the electrons flow (3mks)
      2. Write the reaction of the cell (1mk)
      3. Calculate the e.m.f. of the cell (1mk)
   3. During electrolysis of dilute CUSO4 solution, 0.5 amperes was passed for 3 hours
      1. Write the reactions that took place at the cathode and at the anode (2mks)
         1. Cathode
         2. Anode
      2. Calculate the amount of the solid deposited at the cathode and the amount of Gas liberated at the anode at s.t.p
         1. Solid (2mks)
         2. gas (2mks)
4. The flow chart below outlines some of the process involved in extraction of copper from pyrites
   
   1.    
      1. Name-gas K (1mk)
      2. Write an equation for reaction taking place in the 1st roasting furnace. (1mk)
      3. Name the slag (1mk)
      4. What name is given to the reaction taking place in chamber N? (1mk)
      5. Write the reaction (1mk)
   2. Copper obtained above is not pure. Draw a well labeled diagram to show the set up you would use to refine the copper. (3mks)
   3. Given that the mass of copper obtained from the above extraction was 210kg. Determine percentage purity of the copper pyrite if 810kg of it was fed to the 1st roasting furnace (4mks)
      (CU=64, Fe=56, S=32)
5. Below is an energy level diagram for the reaction
   
   1. Reaction State one condition required for this reaction to occur. (1mk)
   2. Show the activation energy and enthalpy change on the energy level diagram above. (2mks)
   3. Give the following bond energies
      C-C   -   347 Kj/Mol
      C-H   -   413 Kj/Mol
      CL-CL  -  242Kj/Mol
      H-CL   -  431 Kj/Mol
   4. Calculate the enthalpy change of the reaction rate of the above (3mks)
   5. What is the effect of increasing pressure on the reaction rate of the above reaction. Explain (2mks)
   6. Study the reversible reaction below
      2CrO₄^2-_(aq) + 2H⁺_(aq)Cr₂O₇^2-_(aq) + H₂O_(l)
                     yellow                                  orange
      State and explain the observation made when dilute HCl is added to the reaction (3mks)
6.    
   1. Name substance x in the equation below
      C₁₀H₂₂ → X + C₂H₄ 
      X _______________________(1mk)
   2. What is the name of the process (1mk)
   3. Name and write the formula of 3 isomers of hexane (2mks)
   4. Study the flow chart below and answer the questions that follow.
      
      1. Name substances A, B and process X (3mks)
         A            ____________________________
         B            ____________________________
         Process X ____________________________
      2. Name the type of reaction that occurs when ethanol is converted to CH₂=CH₂ (1mk)
      3. Ethanol reacts with propanoic acid to form compound D. Write the structural formula and name of compound D (2mks)
      4. Alkenes can polymerise
         
         Deduce and name the structural formula of the monomer for the structure of the polymer shown above (2mks)
7. Study the scheme below and answer the questions that follow
   
   1. Identify the catalyst used in step I (1mk)
   2. Describe the chemical test of gas E (1mk)
   3. Name the optimum conditions for the production of ammonia gas (2mks)
   4. Identify X and Y and their sources (2mks)
      X________________Source________________
      Y________________Source________________
   5. Write a chemical equation of the reaction between substance c and copper metal (1mk)

MARKING SCHEME

1.    
   1. An element S has an atomic number of 38 and belongs to period 5.
      1. What name is given to the group to which the element belongs? (1mk)
         • Alkaline earth metals
      2. Write the electronic configuration of the element (1mk)
         • 2:8:18:8:2
           
           
   2. The table below gives information about some ions of certain elements. Study it and answer the questions that follow.
      

      Ion	Ionic Configuration	Ionic Radius (nm)	Atomic radii (nm)
      Q2-	2:8	0.136	0.072
      T3+	2:8	0.050	0.143
      W+	2:8	0.095	0.186
      X+	2	0.066	0.152

      
      
      1. Name the nature of the oxide formed when T³⁺ forms an oxide (1mk)
         • Amphoteric oxide
      2. Identify the ion of the most electronegative element (1mk)
         • Q^2-
      3. Compare the reactivity of elements forming ions W⁺ and X⁺ (1mk)
         • W is more reactive than X
      4.    
         1. Draw a 'dot' and 'cross' diagram illustrating on the compound formed when T³⁺ combines with Q^2- (1mk)
            
         2. Name the type of structure formed (1mk)
            • Giant Ionic Structure
              
              
      5. Name the charge carries would be present in:
         1. Chloride formed by W⁺ (1mk)
            • Mobile ions
         2. Element of X⁺ (1mk)
            • Delocalized electrons
              
              
   3. Two elements R and S belong to group VII of the periodic table with atomic numbers 17 and 53 respectively.
      1. State the electronic configuration of the ion R (1mk)
         • 2:8:8
           
           
      2. S is a solid while R is a gas. Explain (1mk)
         • Has larger molecules than R hence stronger Van der Waal forces of attraction
2.    
   1. If chlorine gas is passed over heated iron fillings and the product dissolved in water, a yellow solution is formed.
      1. What would be observed if aqueous ammonia is added to the yellow solution (1mk)
         • A brown precipitate is formed
           
           
      2. Write the ionic equation for the reaction above in (i) (1mk)
         • Fe³⁺_(aq) + 3OH^-_(aq) → Fe(OH)_3(s)
           
           
   2. Study the reaction scheme below and answer the questions that follow.
      
      1. Write the ionic equations for the formation of
         1. Colourless solution X (1mk)
            • Pb(OH)_2(s) + 2OH^-_(aq) → [Pb(OH)]²⁺_(aq)
              
              
         2. Yellow precipitate (1mk)
            • Pb(NO)_3(aq) +2I^-_(aq) → PbI_(s)
              
              
      2. What observations are made when white precipitate S is heated strongly (1mk)
         • Turns from white to orange/ red when hot then yellow on cooling or turns from white to yellow.
           
           
      3. Hydrogen sulphide gas was passed through colourless solution R. Write the equation for the reactions that took place (1mk)
         • Pb(NO₃)_2(aq) + H₂S_(aq) → PbS_(s) + 2HNO_3(aq)
           
           
   3.    
      1. A student was required to prepare a sample of copper metal using crystals of copper II sulphate and iron fillings. Describe how the student would obtain copper metal (3mks)
         • Pass water to copper (II) sulphate crystals and stir to form CuSO, solution.
         • Add iron fillings to the solution and stir.
         • Continue adding iron fillings till the pale blue colour of solution just fades.
         • Filter the mixture to obtain copper metals residue.
         • Wash and dry the residue between filter papers.
           
           
      2. The solution obtained in (i) above was electrolysed using inert electrodes.
         1. Name the product at cathode. (1mk)
            • Hydrogen gas
              
              
         2. Calculate the mass of the product formed at the anode if a current of 0.15A was passed for 1 hour 5 seconds at s.t.p. (molar gas volume - 22.4cm³) (Fe=56, O=16, S=32, CU=63.5) (3mks)
            • Q = It
              = 0.15A x 60 x 60 + 5)
              = 0.15A x 3605
              = 540.75C
              4OH^-_(aq)
              2H₂O_(l) + O_2(g) + 4e^-
              (96500CX 4) yield 32g of O₂
              X =  540.75C x 32  = 0.0448g
                       96500C x 4 
              
              
3. The table below gives reduction potentials obtained when half cells for the following metals; J, K, L, M and N were connected to a copper half cell as reference electrode.
   

   metals	reduction potentials (volts)
   J-	-1.10
   K	-0.47
   L	0.00
   M	+0.45
   N	+1.16

   
   
   1.    
      1. What is metal L likely to be (1mk)
         • Сорреr
           
           Give a reason (1mk)
           It is reference electrode hence Eº of 0.00
           
           
      2. Which metal cannot be displaced from its salt by any other metal in the table (1mk)
   2. If metal Kand M were used as electrodes to form an electrochemical cell
      1. Draw a well labeled diagram of this cell and the direction of the electrons flow (3mks)
         
      2. Write the reaction of the cell (1mk)
         • K_(s) + M²⁺_(aq) → K²⁺_(aq) + M_(s)
           
           
      3. Calculate the e.m.f. of the cell (1mk)
         • +0.45-0.47 = ±0.92V
           
           
   3. During electrolysis of dilute CUSO4 solution, 0.5 amperes was passed for 3 hours
      1. Write the reactions that took place at the cathode and at the anode (2mks)
         1. Cathode
            • Cu²⁺_(aq) + 2e → Cu_(s)
              
              
         2. Anode
            • 4OH^-_(aq) →  2H₂O_(l) + O₂
              
              
      2. Calculate the amount of the solid deposited at the cathode and the amount of Gas liberated at the anode at s.t.p
         1. Solid (2mks)
            • 0.5 x 3 x 60 = 90C
              2 x 96500 - 63.5
              90 = 63.5 x 90   
                      2 x 96500
              = 1.776688
              
              
         2. gas (2mks)
            • 4 x 96500C = 22.41
              90 = 22.4 x 90  
                       4 x 96500
              = 0.00522 litres
              
              
4. The flow chart below outlines some of the process involved in extraction of copper from pyrites
   
   1.    
      1. Name-gas K (1mk)
         • SO₂
           
           
      2. Write an equation for reaction taking place in the 1st roasting furnace. (1mk)
         • 2CuFeS_2(s) + 4O_2(g) → Cu₂S_(s) + 2FeO_(s) + 3SO_2(g)
           
           
      3. Name the slag (1mk)
         • Iron (II) salicate (FeSiO₃)
           
           
      4. What name is given to the reaction taking place in chamber N? (1mk)
         • Redox
           
           
      5. Write the reaction (1mk)
         • Cu₂S_(l) + 2Cu₂O_(l) → 6Cu_(l)+ SO_2(g)
           
           
   2. Copper obtained above is not pure. Draw a well labeled diagram to show the set up you would use to refine the copper. (3mks)
      
      
      
      
   3. Given that the mass of copper obtained from the above extraction was 210kg. Determine percentage purity of the copper pyrite if 810kg of it was fed to the 1st roasting furnace (4mks)
      (CU=64, Fe=56, S=32)
      • 2CuFeS₂ → Cu₂S
        Cu₂S → Cu₂O
        Cu₂O → 3Cu
        Moles of Cu = 210000
                                64.
        = 3.281
        Moles of Cu = 3.28
                               3
        =1.09375
        Moles of Cu₂S = 0.09375
        Moles of CuFeS₂ - 1.09375 x 2 = 2.1875
        Mass of CuFeS₂ = 2.1875 x 151 = 402.5
        % purity = 402.5 x 100
                              810
        = 49.69%
        
        
5. Below is an energy level diagram for the reaction
   
   1. Reaction State one condition required for this reaction to occur. (1mk)
      • U.V light
        
        
   2. Show the activation energy and enthalpy change on the energy level diagram above. (2mks)
      
   3. Give the following bond energies
      C-C   -   347 Kj/Mol
      C-H   -   413 Kj/Mol
      CL-CL  -  242Kj/Mol
      H-CL   -  431 Kj/Mol
      1. Calculate the enthalpy change of the reaction rate of the above (3mks)
         • H = (413 +242) - (346+ 431) = -122kJ
           
           
      2. What is the effect of increasing pressure on the reaction rate of the above reaction. Explain (2mks)
         • Reaction rate increase - Increase in pressure brings reacting particles closer thus increasing the rate of effective collisions.
           
           
   4. Study the reversible reaction below
      2CrO₄^2-_(aq) + 2H⁺_(aq)Cr₂O₇^2-_(aq) + H₂O_(l)
                     yellow                                  orange
      State and explain the observation made when dilute HCl is added to the reaction (3mks)
      • HCl is added to the reaction
      • Intensity of orange colour increases
      • HCl increases H concentration hence equation shifts to the right, more Cr₂O₇^2- is formed.
6.    
   1. Name substance x in the equation below
      C₁₀H₂₂ → X + C₂H₄ (1mk)
      • X -Octane (C₈H₁₈) 
        
        
   2. What is the name of the process (1mk)
      • Cracking
        
        
   3. Name and write the formula of 3 isomers of hexane (2mks)
      • CH₃CH₂CH₂CH₂CH₃
              |
             CH₃
        2-methylpentane
        
        
      •       CH_{3
                 |}
         CH₃CCH₂CH₂CH₃
                |
               CH₃
        2,2-Dimethyl butane
        
        
      • CH₃CH₂CHCH₂CH₃
                    |
                   CH₃
        3-methyl pentane
        
        
   4. Study the flow chart below and answer the questions that follow.
      
      1. Name substances A, B and process X (3mks)
         A - Glucose
         B - yeast
         Process X  - Fractional distillation
         
         
      2. Name the type of reaction that occurs when ethanol is converted to CH₂=CH₂ (1mk)
         • Dehydration
           
           
      3. Ethanol reacts with propanoic acid to form compound D. Write the structural formula and name of compound D (2mks)
         
         Ethyl propanoate
         
         
      4. Alkenes can polymerise
         
         Deduce and name the structural formula of the monomer for the structure of the polymer shown above (2mks)
         
7. Study the scheme below and answer the questions that follow
   
   1. Identify the catalyst used in step I (1mk)
      • Iron
        
        
   2. Describe the chemical test of gas E (1mk)
      • Bring a glowing splint to the mouth of the test tube contravening gas E
      • The glowing splints relights
        
        
   3. Name the optimum conditions for the production of ammonia gas (2mks)
      • Iron catalyst
      • 500 atmospheres
      • 400°C to 500°C 
        
        
   4. Identify X and Y and their sources (2mks)
      X - Nitrogen  Source - From fractional distillation acquired from air
      Y - Hydrogen Source - from contracting of petroleum products
   5. Write a chemical equation of the reaction between substance c and copper metal (1mk)
      • Cu_(s) + 4HNO_3(l) → Cu(NO₃)_2(aq) + 2NO_2(g) + 2H₂O_(l)

        OR
        
        3Cu_(s) + 8HNO_3(aq) → 3Cu(NO₃)_2(aq) + 4H₂O_(l) + 2NO_2(g)