Chemistry Paper 2 Questions and Answers - Moi Kabarak High School Mock 2020/2021

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  • Answer all the questions in the spaces provided
  • Mathematical tables and calculators may be used
  • ALL workings must be clearly shown where necessary
  1. Study the data in the table below and answer the questions. The letters do not represent the actual symbols of the elements.
     Element   Atomic number   Boiling point °C
        P       3      1333
        Q      13       2470
        R      16       445
        S      18     −186
        T      19        774

    1. Select the elements that belong to the same    
      1. Group   (1 mk)
      2. Period    (1 mk)
    2. Which element:
      1. Is a gas at room temperature? Explain.     (2 mks)
      2. Does not take an oxide    (1 mk)
    3. Write the:
      1. Formula of the Sulphate of element Q   (1 mk)
      2. Equation for the reaction between elements P and R   (1 mk)
    4. What type of bonding would exist in the compound formed when elements R and Q react? Give a reason for your answer.  (2 mks)
    5. Select the most electropositive element  (1mk)
    6. Explain why the boiling point of element Q is higher than that of element P.     (2 mks)
  2. In order to determine the imolar heat of neutralization of potassium hydroxide, 200cm3 of 1M Hydrochloric acid and 200cm3 Of IM Potassium hydroxide both at the same initial temperature were mixed and stirred continuously with a thermometer. The temperature of the resulting solution was recorded after every 30 seconds until the highest temperature of the solution was attained. Thereafter, the temperature of the solution was recorded for a further two minutes.
    1.  
      1. Why was it necessary to stir the mixture of the two solutions?    (1 mk)
      2. Define molar heat of neutralization      (1 mk)
      3. Write an ionic equation for the reaction which took place      (1 mk)
    2. If the initial temperature for both solution was 24.5°C and the highest temperature attained by the mixture was 30.9°C.
      Calculate the:
      1. Heat change for the reaction (specific heat capacity of the solution
        = 4.2Jg−1K−1and the density of the solution = 1.0g/cm3      (2 mks)
      2. Molar heat at neutralization of potassium hydroxide.       (2 mks)
    3. Explain how the value of the molar heat of neutralization obtained in the experiment would compare with the one that would be obtained if the experiment was repeated using 200cm3 of 1 Mammonium hydroxide instead of IM potassium hydroxide.  (2 mks)
    4. Use the following information to answer the questions that follow:
      C(s) + O2(g) →  CO2(g)                               ∆H = -393KJ/mol
      H2(g) + ½O2(g) → H20(g)                           ∆H = -296KJ/mol
      13
      C4H10+ 13/2O2(g) → 4CO2(g)+ 5H20       ∆H =-2877K]moi
      Calculate the heat of formation of butane.    (3 mrks)
  3. Aqueous Copper (II) Sulphate was electrolyzed using the set up represented by the diagram below
             electrolysis of Aqueous copper sulphate
    1. After sometimes it was found that no gas was produced at both electrodes. Explain.    (1 mk)
    2. Write an equation for the reaction at each electrode.    (2 mks)
      1. Anode
      2. Cathode
    3. What happens to the colour of the electrolyte during electrolysis. Explain  (2 mks)
    4. An iron spoon is to be electroplated with silver. Draw a labeled diagram of the set-up that could be used to represent the process.     (2 mks)
    5. The following are half-cell equations for some elements. The letters do not represent actual symbols. Use the information to answer the questions that follow.
      Half cell                              Eθ, v
      M2+(aq)+ 2ē → M(s)              +0.34
      L2+(aq)+2ē → L(s)               +0.84
      K2+(aq)+ 2ē → K(s)              -0.13
      J2+(aq) + 2ē + J(s)                  -0.76
      1. Select the two half cells that would produce the highest e.m.f of a cell. (1 mk)
      2. Calculate the e.m.f of the cell in d(i) above.      (2 mks)
      3. Give the cell diagram notation for the cell in d(ii) above.       (1 mk)
  4. The scheme below shows several reactions starting with propanol. Study the scheme and answer the questions which follow.
             reaction starting with propanol
    1. Name gas R      (1 mk)
    2. Name and draw the structural formula of compound Q.    (2 mk)
    3. What conditions and reagents are necessary to convert S to CH3CH2COOCH2CH3      (2 mks)
      Reagents                                     Conditions                                 
    4. Write an equation for the reaction that takes place when equal volumes of chlorine gas react with propane.  (1mk)
    5. The table below shows some properties of organic compounds U, V and W. Use the information to answer the questions that follow.
         W   V   U 
      Reaction with liquid bromine  Decolourises bromine very fast  No reaction  Decolourises bromine liquid slowly
      Combustion Burns with yellow smoky flame  Burns with a blue flame leaving no residue Burns with a yellow sooty flame
      Reaction with Conc.H2SO4 No reaction It is dehydrated to form compound U Reacts to form V
      To which homologous series do the compounds belong?     (3 mks)
      U-
      V-
      W-
    6. CH2 = CH – CH3 when heated under high temperatures and pressures forms a solid with large molecular mass.
      1. Write the equation for the reaction which involves the formation of the solid.     (1 mk)
      2. Name the solid and give one use of the solid     (2 mks)
  5. Study the flow chart below and answer the questions that follow
             A flow chart with questions
    1. Identify gas:
      1. J.....  (1mk)
      2. K...  (1mk)
    2. Write the equation for the reaction that occurs in steps:
      (V)........(1mk)
      (VI)...  (1mk)
    3. Name substance N.....(1mk)
    4. Write an equation for formation of R and explain why high pressure is required in converting J to R  (3 mks)
    5. Give one commercial use of;
      1. Liquid T........(1mk)
      2. Compound Q....(1mk)
    6. Describe a chemical test that would be used to distinguish the anion in compound Q and the product in Step IV  (2 mks)
    7. State and explain the observation made when concentrated sulphuric (VI) is added to crystals of copper (II) Sulphate in a beaker.   (2 mks)
  6.  
    1.  
      1. Give the name of the reagent which when reacted with concentrated hydrochloric acid produce chlorine gas.  (1 mk)
      2. A student out to prepare iron III chloride using the apparatus shown in the diagram below.
                 preparation of Iron IIIchloride
        1. Explain why:
          1. It is necessary to pass chlorine gas through the apparatus before heating begins. (1 mk)
          2. Calcium oxide would be preferred to calcium chloride in the guard tube. (1 mk)
        2. What property of iron (III) chloride makes it possible to be collected as shown in the diagram?  (1mk)
        3. Write an equation form one chemical reaction that took place in the guard tube (1mk)
        4. The total mass of iron (III) chloride formed was found to be 0.5g.
          Calculate the volume of chlorine gas the reacted with iron.
          (Fe - = 56.0, C1 = 35.5 and Molar gas volume at 298K is 24,000cm3       (3 mk)
    2.  
      1. Below is a graph that was obtained when different concentrations of hydrochloric acid was reacted with equal amount of calcium carbonate.
        Different concentrations of hydrochloric acid with calcium carbonate
        The concentrations of hydrochloric acid were 0.8m, 0.5m and 0.1m. The calcium carbonate was in powder form. Match the graphs with concentrations.
        Graph I    (1 mk)
        Graph II      (1 mk)
      2. A state of equilibrium between dichromate (VI) and chromate ions is established as shown in the equation below.
        Cr2O7 (aq) + 20H(aq) double arrows 2CrO4(aq)+ H2O(l)
        Orange                                 Yellow
        State and explain observation made when a few pellets of potassium hydroxide are added to the equilibrium mixture.   (2 mks)

  7.           simplified diagram of a downs cell in sodium manufacture
    1. The above is a simplified diagram of the Downs Cell used for the manufacture of sodium. Study it and answer the questions that follow.
      1. What material is the anode made of? Give a reason    (2 mks)
      2. What precaution is taken to prevent chlorine and sodium from re- combination? (1 mk)
      3. Write an ionic equation for the reaction in which chlorine gas is formed    (1 mk)
    2. In the Downs process, (used for manufacture of sodium), a certain salt is added to lower the melting point of sodium chloride from about 800°C to about 600°C.
      1. Name the salt that is added  (1 mk)
      2. State why it is necessary to lower the temperature      (1mk)
    3. Explain why aqueous sodium chloride is not suitable as an electrolyte for the manufacture of sodium in the Downs process  (2 mks)
    4. Sodium metal reacts with air to form two oxides. Give the formulae of two oxides     (1 mk)


Marking Scheme

  1. Study the data in the table below and answer the questions. The letters do not represent the actual symbols of the elements.
     Element   Atomic number   Boiling point °C
        P       3   2.1      1333
        Q      13  2.8.3       2470
        R      16  2.8.6       445
        S      18  2.8.8     −186
        T      19  2.8.8.1        774

    1. Select the elements that belong to the same    
      1. Group   (1 mk)  
        • P and T 
      2. Period    (1 mk)
        • Q,R & S
    2. Which element:
      1. Is a gas at room temperature? Explain.     (2 mks)
        • S, It's boiling point is below room temperature
      2. Does not take an oxide    (1 mk)
        • S
    3. Write the:
      1. Formula of the Sulphate of element Q   (1 mk)
        • Q2(SO4)3
      2. Equation for the reaction between elements P and R   (1 mk)
        • 2P(s)+R(s)→P2R(s)
    4. What type of bonding would exist in the compound formed when eiements R and Q react? Give a reason for your answer.
      (2 mks)
      • Ionic
        Q transfers it's electrons to R when they react.
    5. Select the most electropositive element  (1mk)
      • T
    6. Explain why the boiling point of element Q is higher than that of element P.     (2 mks)
      • Q has strong metallic bond than P, it has more delocalised electrons hence strong metallic bond
  2. In order to determine the inolar heat of neutralization of potassium hydroxide, 200cm3 of 1M Hydrochloric acid and 200cm3 Of IM Potassium hydroxide both at the same initial temperature were mixed and stirred continuously with a thermometer. The temperature of the resulting solution was recorded after every 30 seconds until the highest temperature of the solution was attained. Thereafter, the temperature of the solution was recorded for a further two minutes.
    1.  
      1. Why was it necessary to stir the mixture of the two solutions?    (1 mk)
        • To ensure heat is evenly distributed in the solution
      2. Define molar heat of neutralization      (1 mk)
        • Enthalpy change when 1mole of a OHare neutralized by 1mole of H+ to form 1 mole of water
      3. Write an ionic equation for the reaction which took place      (1 mk)
        • OH(aq)+ H+(aq)→H2O(l)
    2. If the initial temperature for both solution was 24.5°C and the highest temperature attained by the mixture was 30.9°C.
      Calculate the:
      1. Heat change for the reaction (specific heat capacity of the solution
        = 4.2Jg−1K−1and the density of the solution = 1.0g/cm3)      (2 mks)
        ∆H =400 × 4.2 × 6.4
             =10752J//10.75%
      2. Molar heat at neutralization of potassium hydroxide.       (2 mks)
        Moles of KOH =200 × 1
                                1000
                            =0.2
        0.2→10.752
        1mole→?
        10.752 × 1
              0.2
        =−53.76KJ/mole
    3. Explain how the value of the molar heat of neutralization obtained in the experiment would compare with the one that would be obtained if the experiment was repeated using 200cm3 of 1 Mammonium hydroxide instead of IM potassium hydroxide.
      (2 mks)
      • Ammonium hydroxide is a weak base, it's partially ionized some of the heat is used up to fully ionize. Heat of KOH is higher than ammonium hydroxide
    4. Use the following information to answer the questions that follow:
      C(s) + O2(g) →  CO2(g)                            AH = -393KJ/mol
      H2(g) + ½O2(g) → H20(g)                        AH = -296KJ/mol
      C4H1013/2O2(g) → 4CO2(g)+ 5H20    AH =-2877K]moi
      Calculate the heat of formation of butane.    (3 mrks)
      Calculation of formation of butane 
      ∆H=4x − 393 + 5x −296−−2877
          =−1572+−1480−−2877
      =−175KJ/mole
  3. Aqueous Copper (II) Sulphate was electrolyzed using the set up represented by the diagram below
    1. After sometimes it was found that no gas was produced at both electrodes. Explain.    (1 mk)
      • At the cathode,Cu2+ are preferential discharged
      • At the anode Cu solid is discharged
    2. Write an equation for the reaction at each electrode.    (2 mks)
      1. Anode
        • Cu(s) → Cu2+(aq) + 2e 
      2. Cathode
        • Cu2+(aq) + 2e → Cu(s)
    3. What happens to the colour of the electrolyte during electrolysis. Explain   (2 mks)
      • Blue color remains blue Cu2+ removed are replaced by Cu dissolving at anode
    4. An iron spoon is to be electroplated with silver. Draw a labeled diagram of the set-up that could be used to represent the process.     (2 mks)
      Labelled diagram of Electrochemical cellusing half cells
    5. The following are half-cell equations for some elements. The letters do not represent actual symbols. Use the information to answer the questions that follow.
      Half cell                              Eθ, v
      M2+(aq)+ 2ē → M(s)              +0.34
      L2+(aq)+2ē → L(s)               +0.84
      K2+(aq)+ 2ē → K(s)              -0.13
      J2+(aq) + 2ē + J(s)                  -0.76
      1. Select the two half cells that would produce the highest e.m.f of a cell. (1 mk)
        L(s)/L2+(aq),     a-d     J(s)/J2+(aq)
      2. Calculate the emf of the cell in d(i) above.      (2 mks)
        +0.84−−a76 =+1.60v
      3. Give the cell diagram notation for the cell in d(ii) above.       (1 mk)
         J(s)/J2+(aq)//L(s)/L2+(aq),Eθ=1.60v 
  4. The scheme below shows several reactions starting with propanol. Study the scheme and answer the questions which follow.
    1. Name gas R      (1 mk)
      • Hydrogen
    2. Name and draw the structural formula of compound Q.    (2 mks)
      Propene
      structural formula of compound q
    3. What conditions and reagents are necessary to convert S to CH3CH2COOCH2CH3      (2 mks)
      Reagents Ethanol  Conditions  1. Drops of Conc. H2SO4    2. Warm
    4. Write an equation for the reaction that takes place when equal volumes of chlorine gas react with propane.     (1 mk)
      CH3CH2CH3(g) + Cl2(g) → CH3CH2CH2Cl +HCL
    5. The table below shows some properties of organic compounds U, V and W. Use the information to answer the questions that follow.
         W   V   U 
      Reaction with liquid bromine  Decolourise bromine very fast  No reaction  Decolourises bromine liquid slowly
      Combustion Burns with yellow smoky flame  Burns with a blue flame leaving no residue Burns with a yellow sooty flame
      Reaction with Conc.H2SO4 No reaction It is dehydrated to form compound U Reacts to form V
      To which homologous series do the compounds belong?     (3 mks)
      U-Alkene
      V-Alkanol
      W-Alkyne
    6. CH2 = CH – CH3 when heated under high temperatures and pressures forms a solid with large molecular mass.
      1. Write the equation for the reaction which involves the formation of the solid.     (1 mk)
        n(CH2=CHCH3)→  reaction involving formation of a solid
      2. Name the solid and give one use of the solid     (2 mks)
        • Polypropene
          Making ropes,crates
  5. Study the flow chart below and answer the questions that follow
    1. Identify gas:
      1. Sulphur (IV) Oxide (1mk)
      2. Nitrogen(II)Oxide  (1mk)
    2. Write the equation for the reaction that occurs in steps:
      (V)   NH4NO3(s)→  N2O(g) + 2H2O(l)        (1mk)
      (VI)  SO3(g) + H2SO4(l) →  H2S2O7(l)                      (1mk)
    3. Name substance N   Vanadium (VI) Oxide (1mk)
    4. Write an equation for formation of R and explain why high pressure is required in converting J to R  (3 mks)
      2SO2(g)+O2(g) → 2SO3(g)
      Forward reaction leads to reduction in volume, high pressure is required to reduce the volume
    5. Give one commercial use of;
      1. Liquid T   Manufacture of fertilizer, Dyes, drugs, paints (1mk)
      2. Compound Q    As a fertilizer    (1mk)
    6. Describe a chemical test that would be used to distinguish the anion in compound Q and the product in Step IV  (2 mks)
      Product  SO42−/NO3
      Chemical test; To each sample add barium Nitrate for SO42− a white preicpitate is formed for NO3,no white precipitate
    7. State and explain the observation made when concentrated sulphuric (VI) is added to crystals of copper (II) Sulphate in a beaker.   (2 mks)
      • Blue crystals changes to white powder
      • Conc H2SO4 dehydrates hydrated copper sulphate
  6.  
    1.  
      1. Give the name of the reagent which when reacted with concentrated hydrochloric acid produce chlorine gas.  (1 mk)
        • Lead(IV)Oxide/ Manganese(IV)Oxide/Potassium Manganate(IV)
      2. A student out to prepare iron III chloride using the apparatus shown in the diagram below.
        1. Explain why:
          1. It is necessary to pass chlorine gas through the apparatus before heating begins. (1 mk)
            • To prevent iron from being oxidized
          2. Calcium oxide would be preferred to calcium chloride in the guard tube. (1 mk)
            • It also absorbs Cl2, preventing it from escaping to the atmosphere.
        2. What property of iron (III) chloride makes it possible to be collected as shown in the diagram?     (1 mk)
          • It sublimes when heated
        3. Write an equation form one chemical reaction that took place in the guard tube (1mk)
          Cl2(g) +CaO(s) → CaOCl2(s)
        4. The total mass of iron (III) chloride formed was found to be 0.5g.
          Calculate the volume of chiorine gas the reacted with iron.  (3 mk)
          (Fe - = 56.0, C1 = 35.5 and Molar gas volume at 298K is 24,000cm3       
          2Fe(s) + 3Cl2(g) → 2FeCl3(s)
          Moles of FeCl30.5/162.5
                               =0.00308moles
          Mole ratio 
          FeCl3: Cl2  
                2:3
          0.00308  ?
          0.00308×3/2
          0.00462 × 24000 
             =110.88cm3
           
    2.  
      1. Below is a graph that was obtained when different concentrations of hydrochloric acid was reacted with equal amount of calcium carbonate.
        The concentrations of hydrochloric acid were 0.8m, 0.5m and 0.1m. The calcium carbonate was in powder form. Match the graphs with concentrations.
        Graph I   0.8   (1 mk)
        Graph II  0.5    (1 mk)
      2. A state of equilibrium between dichromate (VI) and chromate ions is established as shown in the equation below.
        Cr2O7 (aq) + 20H−(aq) double arrows 2CrO4(aq)+ H2O(l)
        Orange                                 Yellow
        State and explain observation made when a few pellets of potassium hydroxide are added to the equilibrium mixture.   (2 mks)
        • Mixture becomes yellow
        • KOH increases concentration of OH hence forward reaction is favoured
  7.  
    1. The above is a simplified diagram of the Downs Cell used for the manufacture of sodium. Study it and answer the questions that follow.
      1. What material is the anode made of? Give a reason    (2 mks)
        • Graphite
          Does not react with products of electrolysis.
      2. What precaution is taken to prevent chlorine and sodium from re- combination? (1 mk)
        • Steel gauze diaphram is used to separate the Anode from cathode
      3. Write an ionic equation for the reaction in which chlorine gas is formed    (1 mk)
        2Cl(aq) → Cl2(g) + 2e
    2. In the Downs process, (used for manufacture of sodium), a certain salt is added to lower the melting point of sodium chloride from about 800°C to about 600°C.
      1. Name the salt that is added  (1 mk)
        • Cryolite
      2. State why it is necessary to lower the temperature      (1mk)
        • Reduce the amount of energy used hence lower cost
    3. Explain why aqueous sodium chloride is not suitable as an electrolyte for the manufacture of sodium in the Downs process  (2 mks)
      • H+ will be preferentially discharged hence H2(g) will be produced instead of Na.
    4. Sodium metal reacts with air to form two oxides. Give the formulae of two oxides     (1 mk)
      Na2O(s)/Na2O2

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