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Chemistry Paper 2 Questions and Answers - Royal Exam Series Post Mock Trial Exams 2022

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CHEMISTRY
PAPER 2
THEORY

INSTRUCTIONS TO CANDIDATES

  • Write your name and Index number in spaces provided above.
  • Sign and write the date of examination in the spaces provided above.
  • This paper contains 11 printed pages.
  • Answer all the questions in the spaces provided above.
  • KNEC Mathematical tables and silent electronic calculators may be used.
  • All working must be clearly shown where necessary.
  • Candidates should answer the questions in English.

Questions

  1. Below is part of the periodic table. The letters are not the actual symbols of the elements. Study it and answer the questions that follow.
    ChemPstMp2Q1
    1.            
      1. State and explain the difference in the melting points of D and F (2mks)
      2. Explain the difference in the atomic radii of G and N. (2mks)
      3. Select the element that is the strongest reducing agent. Explain. (2mk)
      4. Compare the nature of the aqueous solution of the oxide of C and that of L. explain. (2mks)
    2. Study the table below and answer the questions that follow.
      SUBSTANCE  M.P(K)  B.P(K)  ELECTRICAL
      CONDUCTIVITY  
      SOLID MOLTEN
       J  365  463 NIL NIL
       K  1323  2773 GOOD GOOD
       L  1046  1680 NIL GOOD
       M  2156  2776 NIL  NIL 
    3. Which of the substances J, K, L and M represent the following;
      1. Silicon (IV) oxide(1mk)
      2. Barium sulphate(1mk)
    4. In terms of structure and bonding, explain why silicon (IV) Chloride (SiCl4) is a liquid at room temperature while Magnesium (MgCl2) is a solid. (2mks)
  2. The diagram below represents a charcoal burner. Study it and answer the questions that follow.
    ChemPstMp2Q2
    1. Write equations for the reactions taking place at (3mks)
      1.       
      2.       
    2. State the color of the flame. (1mk)
    3. The ash that collects in the lower compartment was dissolved in water and filtered.
      Suggest the PH of the solution. (1mk)
    4. Carbon (II) oxide can be prepared in the laboratory by a process represented below.
                           ConH2SO4
      (COOH) 2            →          CO2(g) + CO(g) + H2O(l)
      1. What role does concentrate Sulphuric (VI) acid play in the reaction. (1mk)
      2. How would you remove carbon (IV) oxide from carbon (II) oxide? (1mk)
  3. The diagram below represents a set-up that was to obtain dry nitrogen from air. Study it and answer the questions that follow.
    ChemPstMp2Q3
    1.                           
      1. State the observation in the in the tube P (1mk)
      2. What is the purpose of NaOH(aq)? (1mk)
      3. Write an equation for the reaction which took place in tube P (1mk)
      4. Give the name of one impurity in the nitrogen gas obtained. (1mk)
      5. Why is liquid nitrogen used for storage of semen for artificial insemination? (1mk)
    2. The set-up below was used to prepare nitric acid
      ChemPstMp2Q3b
      1. Give the name of liquid R (1mk)
      2. Write an equation for the reaction which took place in the glass retort. (1mk)
      3. Explain the following
        1. Nitric acid is not stored in transparent glass. (2mks)
        2. The reaction between copper metal with 50% nitric acid (one volume of acid added to an equal volume of water) in an open test tube forms brown fumes. (2mks)
  4. The diagram below shows the set-up of the apparatus used by a student to determine the enthalpy change of combustion of ethanol. The heat produced by burning fuel warms a known mass of water.
    ChemPstMp2Q4
    Results
    • Volume of water in the beaker = 500 cm3
    • Initial temperature of water= 12ºC
    • Final temperature of water = 31.5ºC
    • Mass of ethanol burnt = 1.50g
    • Density of water = 1 g/cm3
    • Specific heat capacity = 4.2 Jg-1K-1
      1. Define molar heat of combustion. (1 mark)
      2.        
        1. Calculate the heat required to raise the temperature of the water from 12ºC to 31.5ºC. (2 marks)
        2. Find the molar enthalpy of combustion of ethanol. (2 marks)
      3. An accurate value for ΔHC of ethanol is -1368 kJmol-1. State two sources of errors for the low figure obtained. (2 marks)
      4. Draw an energy level diagram for the combustion of ethanol. (3 marks)
      5. Calculate the heating value of ethanol from the above experiment. (2 marks)
      6. State one factor that one may consider when choosing kerosene as a fuel in Kisii town. (1 mark)
  5.           
    1. Sulphur is extracted from underground deposits by a process in which three concentric pipes aresunk down to the deposits as shown below
      ChemPstMp2Q5a
      1. Give the name of the process mentioned above ( 1mark)
      2. State two physical properties of Sulphur that makes it to be extracted by this method (2marks).
      3. Why is it necessary to use superheated water in this process (1mark)
      4. During Frasch process molten sulphur flows out through the middle pipe but not through the outer pipe. Give a reason ( 1mark)
    2. The diagram below shows part of the processes in the manufacture of sulphuric (VI) acid. Study and answer the questions that follow.
      ChemPstMp2Q5b
      1. Write an equation for the formation of Sulphur (IV) oxide from Sulphur. (1mk)
      2. What is the role of concentrated sulphuric (VI) acid in chamber A.(1 mark)
      3. Name two catalyst that can be used in the catalytic chamber B.(2 marks)
      4. Give two reasons why during the manufacture of sulphuric (VI) acid, Sulphur (VI) Oxide, is dissolved in concentrated Sulphuric (VI ) acid instead of dissolving in water (2 marks)
    3. Explain one way in which Sulphur (IV) oxide is a pollutant. (1mark)
    4. What observation will be made when a few drops of concentrated sulphuric (VI) acid are added to crystals of sugar? Explain your answer. (2marks)
  6.         
    1. Define solubility. (1 mark)
    2. The table below shows solubility of two salts X and Y at varying temperatures.
      Temperature(ºC) 10 20 30 40 50 60 70 80 90
      Solubility of Y
      (g/100g water)      		 70.0 66.0 63.0 60.0 59.0 56.5 54.5 53 51
      Solubility of X
      (g/100g water)      		 12.0 18.0 24.0 31.0 38.0 48.0 51.0 74.0 88.0

      1. Draw the graph of solubility against temperature. (3 marks)
      2. At what temperature is the solubility of both X and Y the same? (1 mark)
      3. Which of the substances X and Y is likely to be a gas? Explain. (2 marks)
      4. What is the mass of Y that would dissolve in 50g of water at 480C?(1 mark)
      5. Determine the solubility of salt X at 550C? (2 marks)
      6. State one application of solubility. (1 mark)
  7. Study the flow chart below and answer the questions that follow.
    ChemPstMp2Q7
    1.                   
      1. Identify reagent L (1mk)
      2. Name the catalyst used in step 5 (1mk)
      3. Draw the structural formula of gas J (1mk)
      4. What name is given to the process that takes place in step 5 (1mk)
      5. State one use of product R (1mk)
    2.              
      1. Write the equation for the reaction between aqueous sodium hydroxide and aqueous ethanoic acid (1mk)
      2. Explain why the reaction between 1g of sodium carbonate and 2M hydrochloric acid is faster than the reaction between 1g of sodium carbonate and 2M ethanoic acid. (2mks)
    3. Larger alkanes can be broken down into smaller molecules
      1. Give the name for the process (1mk)
      2. Apart from smaller chain alkanes mention the other two smaller molecules (1mk)
    4. Give the systematic names of the following compounds:

      1. ChemPstMp2Q7di (1mk)
      2. CH3CHCH........................................ (1mk)

Marking Scheme

  1. Below is part of the periodic table. The letters are not the actual symbols of the elements. Study it and answer the questions that follow.
    ChemPstMp2Q1
    1.            
      1. State and explain the difference in the melting points of D and F (2mks)
        F has a higher melting point than D because it has a greater muclear charge.
      2. Explain the difference in the atomic radii of G and N. (2mks)
        G has a larger atomic radius than N. N has a greater nuclear charge thus pulls electrons closer to the nucleus reducing the atomic radius.

      3. Select the element that is the strongest reducing agent. Explain. (2mk)
        D has the largest atomic radius thus easily looses its electrons

      4. Compare the nature of the aqueous solution of the oxide of C and that of L. explain. (2mks)
        Oxide of C is basic/ alkaline while oxide of L is acidic. This is because oxide of C dissolves in water to form OH- while oxide of L H+
    2. Study the table below and answer the questions that follow.
      SUBSTANCE  M.P(K)  B.P(K)  ELECTRICAL
      CONDUCTIVITY  
      SOLID MOLTEN
       J  365  463 NIL NIL
       K  1323  2773 GOOD GOOD
       L  1046  1680 NIL GOOD
       M  2156  2776 NIL  NIL 
    3. Which of the substances J, K, L and M represent the following;
      1. Silicon (IV) oxide(1mk)
        M
      2. Barium sulphate(1mk)
        L
    4. In terms of structure and bonding, explain why silicon (IV) Chloride (SiCl4) is a liquid at room temperature while Magnesium (MgCl2) is a solid. (2mks)
      SiCl4 contains simple molecular structure with weak Van der Waal forces while MgCl2 has giant ionic structure with stronger ionic bond.
  2. The diagram below represents a charcoal burner. Study it and answer the questions that follow.
    ChemPstMp2Q2
    1. Write equations for the reactions taking place at (3mks)
      1.  2CO(g) + O2(g) → 2CO2(g)      
      2.  CO2(g) + C(s) → 2CO(g)     
      3. C(s) + O2(g) → CO2(g)

    2. State the color of the flame. (1mk)
      Blue
    3. The ash that collects in the lower compartment was dissolved in water and filtered.
      Suggest the PH of the solution. (1mk)
      pH = 8, 9 or 10. 
      Reject the range

    4. Carbon (II) oxide can be prepared in the laboratory by a process represented below.
                           ConH2SO4
      (COOH) 2            →          CO2(g) + CO(g) + H2O(l)
      1. What role does concentrate Sulphuric (VI) acid play in the reaction. (1mk)
        Dehydrating agent/ Removes elements of water from oxalic acid
      2. How would you remove carbon (IV) oxide from carbon (II) oxide? (1mk)
        Pass the gaseous mixture though KOH or NaOH
  3. The diagram below represents a set-up that was to obtain dry nitrogen from air. Study it and answer the questions that follow.
    ChemPstMp2Q3
    1.                           
      1. State the observation in the in the tube P (1mk)
        A black solid/ deposit is formed

      2. What is the purpose of NaOH(aq)? (1mk)
        To absorb CO2(g)
      3. Write an equation for the reaction which took place in tube P (1mk)
        2Cu(s) + O2(g) → 2CuO(s)
        Must be balanced

      4. Give the name of one impurity in the nitrogen gas obtained. (1mk)
        Noble gas/ Argon
      5. Why is liquid nitrogen used for storage of semen for artificial insemination? (1mk)
        Has a low temperature
    2. The set-up below was used to prepare nitric acid
      ChemPstMp2Q3b
      1. Give the name of liquid R (1mk)
        Concentrated sulphuric (vi) acid.
        Penalise fully dil H2SO4

      2. Write an equation for the reaction which took place in the glass retort. (1mk)
        KNO3(aq) + H2SO4(l) → KHSO4(s) + HNO3(aq)
      3. Explain the following
        1. Nitric acid is not stored in transparent glass. (2mks)
          Easily decompose when exposed to light hence forming NO2(g) and H2O(l)
        2. The reaction between copper metal with 50% nitric acid (one volume of acid added to an equal volume of water) in an open test tube forms brown fumes. (2mks)
          NO. Gas produced reacts with atmospheric air (O2) forming NO2(g), which is brown in colour.
  4. The diagram below shows the set-up of the apparatus used by a student to determine the enthalpy change of combustion of ethanol. The heat produced by burning fuel warms a known mass of water.
    ChemPstMp2Q4
    Results
    • Volume of water in the beaker = 500 cm3
    • Initial temperature of water= 12ºC
    • Final temperature of water = 31.5ºC
    • Mass of ethanol burnt = 1.50g
    • Density of water = 1 g/cm3
    • Specific heat capacity = 4.2 Jg-1K-1
      1. Define molar heat of combustion. (1 mark)
        Enthalpy change that occurs when 1 mole of a substance is completely burnt in oxygen.
      2.        
        1. Calculate the heat required to raise the temperature of the water from 12ºC to 31.5ºC. (2 marks)
          MCΔT
          ΔT= 31.5 - 12 = 19.5ºC
          500g x 4.25/gK x 19.5K
          = 40 950J or 40.95KJ

        2. Find the molar enthalpy of combustion of ethanol. (2 marks)
          R.F.M of C2H5OH = 46
          Moles of C2H5OH = 1.5/46
          = 0.0326
          If 0.0326 = 40.95KJ
          1 mole = ?
          1 x 40.95
            0.0326
          = -1,256.1 KJ mol-1
          = -1,256,134.9 J mol-1

      3. An accurate value for ΔHC of ethanol is -1368 kJmol-1. State two sources of errors for the low figure obtained. (2 marks)
        Heat lost to the surrounding is noot accounted for
        Faulty apparatus

      4. Draw an energy level diagram for the combustion of ethanol. (3 marks)
        ChemPstMp2Qa4d
      5. Calculate the heating value of ethanol from the above experiment. (2 marks)
        | -1,256.1/46 | 
        = 276.31KJg-1

      6. State one factor that one may consider when choosing kerosene as a fuel in Kisii town. (1 mark)
        Heat value
        Availability
        Ease of storage
        Cost
        Rate of combustion
        Ease of transportation

  5.           
    1. Sulphur is extracted from underground deposits by a process in which three concentric pipes aresunk down to the deposits as shown below
      ChemPstMp2Q5a
      1. Give the name of the process mentioned above ( 1mark)
        Frasch process
      2. State two physical properties of Sulphur that makes it to be extracted by this method (2marks).
        Low melting point of 118ºC
        Insoluble in water
        Less denser in water

      3. Why is it necessary to use superheated water in this process (1mark)
        To melt the sulphur
      4. During Frasch process molten sulphur flows out through the middle pipe but not through the outer pipe. Give a reason ( 1mark)
        Molten sulphur would have lost heat to the surrounding hence solidify in the middle pipe. 
        Sulphur cannot solidify since hot air in the inner pipe and hot water in the outer pipe mainatin high temperature

    2. The diagram below shows part of the processes in the manufacture of sulphuric (VI) acid. Study and answer the questions that follow.
      ChemPstMp2Q5b
      1. Write an equation for the formation of Sulphur (IV) oxide from Sulphur. (1mk)
        S(s) + O2(g) → SO2(g)

      2. What is the role of concentrated sulphuric (VI) acid in chamber A.(1 mark)
        To dry SO2 and air
        Reject dry the gases

      3. Name two catalyst that can be used in the catalytic chamber B.(2 marks)
        Platinum wire
        Vanadium(v) oxide
        Reject state symbols

      4. Give two reasons why during the manufacture of sulphuric (VI) acid, Sulphur (VI) Oxide, is dissolved in concentrated Sulphuric (VI ) acid instead of dissolving in water (2 marks)
        Excessive heat generated boild the acid forming a mist of fine droplets of H2SO4 in air
        In  water the acid condenses slowly 

    3. Explain one way in which Sulphur (IV) oxide is a pollutant. (1mark)
      SO2 dissolves in moisture in air forming H2O3. Which is further oxidised to H2SO4 by oxygen in air and comes down as acid rain.

    4. What observation will be made when a few drops of concentrated sulphuric (VI) acid are added to crystals of sugar? Explain your answer. (2marks)
      White/ brown crystals of sugar turns to black because sugar is reduced to carbon
  6.         
    1. Define solubility. (1 mark)
      This is the maximum mass of a solute required to saturate 100g of the solvent at a particular temperature.
    2. The table below shows solubility of two salts X and Y at varying temperatures.
      Temperature(ºC) 10 20 30 40 50 60 70 80 90
      Solubility of Y
      (g/100g water)      		 70.0 66.0 63.0 60.0 59.0 56.5 54.5 53 51
      Solubility of X
      (g/100g water)      		 12.0 18.0 24.0 31.0 38.0 48.0 51.0 74.0 88.0

      1. Draw the graph of solubility against temperature. (3 marks)
        ChemPstMp2Qa5d
      2. At what temperature is the solubility of both X and Y the same? (1 mark)
        67.0ºC + 0.5
      3. Which of the substances X and Y is likely to be a gas? Explain. (2 marks)
        This is because solubility of gases decreases with increase in temperature
      4. What is the mass of Y that would dissolve in 50g of water at 480C?(1 mark)
        58 ± 0.5
             2
        Must be shown in the graph

      5. Determine the solubility of salt X at 550C? (2 marks)
        43 ± 0.5g/100g H2O
        Must be  shown on the graph

      6. State one application of solubility. (1 mark)
        Salting out of soap
        Fractional crystalization
        Purification of common salt

  7. Study the flow chart below and answer the questions that follow.
    ChemPstMp2Q7
    1.                   
      1. Identify reagent L (1mk)
        Calcium carbide
      2. Name the catalyst used in step 5 (1mk)
        Phosphoric (v) acid
      3. Draw the structural formula of gas J (1mk)
        ChemPstMp2Qa7aiii

      4. What name is given to the process that takes place in step 5 (1mk)
        Hydrolysis
      5. State one use of product R (1mk)
        Making rain  coats
        Plastic water pipes
        Electrical insulation
        Floor tiles

    2.              
      1. Write the equation for the reaction between aqueous sodium hydroxide and aqueous ethanoic acid (1mk)
        CH3COOH(aq) + NaOH(aq) → CH3CO-ONa(aq) + H2O(l)
      2. Explain why the reaction between 1g of sodium carbonate and 2M hydrochloric acid is faster than the reaction between 1g of sodium carbonate and 2M ethanoic acid. (2mks)
        HCl is fully dissociated while ethanoic acid dissociates partially tehrefore ethanoic acid is weak HCL is strong.
    3. Larger alkanes can be broken down into smaller molecules
      1. Give the name for the process (1mk)
        Cracking
      2. Apart from smaller chain alkanes mention the other two smaller molecules (1mk)
        methane
        Alkenes eg,  ethene

    4. Give the systematic names of the following compounds:

      1. ChemPstMp2Q7di (1mk)
        1- butene

      2. CH3CHCH........................................ (1mk)

 

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Read 9806 times Last modified on Wednesday, 02 February 2022 07:23

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