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Chemistry Paper 2 Questions and Answers - Sunrise Pre Mock Exams 2023

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INSTRUCTIONS TO CANDIDATES

  • Answer all the questions in the spaces provided below each question. .
  • 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.
  1.  
    1. The table below shows the atomic numbers of elements in the periodic table represented by the letters A to I. The letters are not the actual symbols of the elements.
       Element  A    B   C   D   E   F   G   H  I
       Atomic Number  3  7  8  9  11  12   13   14  16
      1. Select two elements in the same group. (1 mk)
      2. Select the non-metal and the metal that would react most vigorously with each other. (1 mk)
    2.  
      1. Draw cross (X) and dots(●) diagram to show bonding in the compound formed between hydrogen and element B (1 mk)
      2. The compound formed in b(i) above does not conduct electric current in gaseous form but conducts in aqueous form. Explain. (2 mks)
    3. Explain the difference between the melting points of the oxides of H and I (2 mks)
    4. Write an equation for the reaction that takes place between elements G and C. (1 mk)
  2.  
    1. When few drops of ammonia solution was added to hydroxides of zinc, copper and Iron(III), the following solution were obtained; colourless solution, deep blue solution and brown precipitate. Identify the substances responsible for;
      1. Deep blue solution (1 mk)
      2. Colourless solution (1 mk)
      3. Brown precipitate (1 mk)
    2. A saturated solution of potassium chloride is to be prepared at 40°C. Its solubility at 40°C is 34g/100g water and 27g/100g of water at 5°C .
      1. What mass of water would be saturated with 8.5g of potassium chloride at 40°C?(1mk)
      2. What mass of potassium chloride would crystallize out if the saturated solution at 40°C is cooled to 5°C?   (1 mk)
    3. Given two samples of sodium carbonate and sodium hydrogen carbonate. Describe a chemical test that would distinguish them. (2 mks)
    4. Two equal pieces of magnesium ribbon were placed in two separate test tubes, one containing 10cm3 of water and the other containing 10cm3 of methylbenzene. State and explain the observations made in the two test tubes. (2 mks)
    5. In an experiment, soap solution was added to three separate samples of water. The table below shows the volumes of soap solution required to form lather with 2 litres of each sample of water before and after boiling.
       Sample  Sample A   Sample B   Sample C 
       Volume of soap before water is boiled (cm3 )  30  3   13 
       Volume of soap after water is boiled (cm3 )   30  3   3 
      1. Which sample is likely to be soft water? Explain. (2 mks)
      2. Explain the change in volume of soap used in Sample C. (1 mk)
  3.  
  1. 12.0cm 3 of 0.05M hydrochloric acid reacted completely with calcium hydrogen carbonate solution.
    1. Write the chemical equation for the reaction. (1 mk)
    2. Calculate the number of moles of hydrochloric acid used. (1 mk)
    3. Determine the number of moles of calcium hydrogen carbonate used. (1 mk)
  2. Study the flow chart below and answer the questions that follow.
    ChemSRF42023PrMP2Q3b
    1. Name
      1. Gas K. (1 mk)
      2. Gas M (1 mk)
    2. Steps 1, 2 and 3 constitute the contact process. State optimum conditions necessary for step 2 to occur. (1 mk)
    3. Explain what happens in step 4. (2 mks)
    4. Explain why water is not used in step 3 . (1 mk)
    5. Write an equation to show how pollution effects of sulphur (IV) oxide is controlled in contact process.  (1 mk)
    6. State two uses of sulphur. (2 mks)
  •  
    1. Use the bond energies below to answer the questions that follow.
       Bond  Bond energy (KJ/Mol) 
       H-H  436
       C=C  612
       C-C  347
       C-H   413
      Determine the enthalpy for the following reaction
      C4H8(g) + H2(g) → C4H10(g) (3 mks)
    2. Molar enthalpy of combustion of propanol is −1560Kjmol-1 .
      1. Write a thermochemical equation for the complete combustion of propanol. (1 mk)
      2. Calculate the amount of energy in joules released when 10g of propanol is burnt in excess oxygen. (C=12, H = 1.0,O=16.0) (2 mks)
    3.  
      1. State Hess’ law (1 mk)
      2. Use the information below to answer the questions that follow.
        C(s) + O2(g) → CO2(g)                                   Δ Hθ = - 393Kjmol -1
        H2(g) + ½O2(g) → H2O(l)                               ΔHθ  = -287 Kjmol -1
        C3H8 + 5O2(g) → 3CO2(g) + 4H2O(l)             ΔHθ  = -2209kj mol -
        1. What does the symbol ΔHθ represent? (1 mk)
        2. Write the equation for the formation of propane from its constituent elements. (1 mk)
        3. With the aid of an energy cycle diagram, calculate the enthalpy of formation of propane.  (3 mks)
  • The flow chart below shows an analysis of mixture K that contains two salts. Study it and answer the questions that follow.
    ChemSRF42023PrMP2Q5
    1. Identify,
      1. Solution L: (1 mk)
      2. Solid M: (1 mk)
      3. Solution N:  (1 mk)
    2. What condition is necessary in step 1 (1 mk)
    3. State the observations made in step 1 (1 mk)
    4. Write down an equation to show how;
      1. Solution N is formed. (1 mk)
      2. Colourless solution A and Ammonia gas are formed. (1 mk)
    5. When excess NaOH(aq) is added to solution N, a white precipitate is formed which dissolves. Give the name and formula of the ion formed. (2 mks)
      1. Name:……………………………………………………………………………………………….
      2. Formula: …………………………………………………………………………………………….
    6. Explain why it is necessary to add water to mixture K and then filter. (1 mk)
  • A student set up the apparatus shown below to prepare and collect dry carbon (IV) oxide gas.
    ChemSRF42023PrMP2Q6
    1. State a correction for three mistakes in the set up above (3 mks)
    2. Give two reasons why carbon (IV) oxide is used as a fire extinguisher (2 mks)
    3. The flow chart below is for the manufacture of sodium carbonate by the Solvay process. Use it to answer the questions that follow.
      ChemSRF42023PrMP2Q6c
      1. Name gas
        1. M: ………………………….. (1 mk)
        2. Q: …………………………..
      2. Name solution F and solid X (1 mk)
        1. F: ………………………………………………………..
        2. X: ……………………………………………………….
      3. Name the product L formed and give one of its uses (2 mks)
      4. Write equations of the reactions in (2 mks)
        1. Tower:
        2. Chamber K:
      5. Name the two raw materials required in the manufacture of sodium carbonate (2 mks)
  • A piece of marble chip (calcium carbonate) is put in a beaker containing excess of dilute hydrochloric acid which is placed on a reading balance. The mass of the beaker and its contents is recorded every two minutes as shown in the table.
     Time (min)  0  2   4   6   8   10   12 
     Mass (g)  126.4  126.3   126.2   126.1   126.0   126 0  126.0 
    1. Why is there a continuous loss of mass of the reaction mixture. (1 mk)
    2. Write an equation for the reaction taking place. (1 mk)
    3. State two different ways by which the reaction could have been made more rapid. (2 mks)
    4. Why does the mass remain constant after 8 minutes (1 mk)
    5. State the observations that would be made if a few drops of lead II nitrate solution was added to 1cm3 of the resulting solution followed by excess ammonia solution.   (2 mks)
    6. State one environmental effect that excess carbon (IV) oxide in the air causes. (1 mk)
    7. The energy profile for the forward direction of a reversible reaction is shown.
      ChemSRF42023PrMP2Q7
      Sketch on the diagram the path for a catalysed reaction. (1 mk)
    8. What do you observe when you introduce the following substances in this equation
      2CrO2-4(aq) + 2H+(aq)   Screenshot 2023 05 31 at 15.13.14 Cr2O2-7(aq) + H2O (l)                  ΔH= −477Kj/Mol
      Yellow                                           Orange
      1. Dilute hydrochloric acid solution. Explain (2 mks)
      2. Increase heat.  (2 mks)

    • MARKING SCHEME

    1.  
      1.  
        1.  
          1. A and E / C and I √1               Any for 1mk
          2. D and E   √1
      2.  
        1.    
          ChemSRF42023PrMP2Ans1a        
        2. In gaseous form the compound lack mobile ions while in aqueous state it is in ionic form hence conduct electric current √1
      3. Melting point of oxide of H is higher than that of  oxide of I;H oxide have Giant covalent structure with strong covalent bond √1 while oxide of I have simple molecular structure with weak intermolecular bond √1                                                                                             2mks
      4. 4G + 3C2(g) → 2G2C3(s)
        OR    √
        4Al(s) + 3O2(g) → 2Al2O3(s) √1
    2.  
      1.  
        1. Tetraammine copper (ii) ions √1
        2. Tetraammine zinc (II) ions √1
        3. Iron (III) hydroxide. √1
      2.  
        1. 34g of KCl   Screenshot 2023 05 31 at 09.33.19100g of H2O  √ ½
          8.5g of KCl   Screenshot 2023 05 31 at 09.33.198.5 × 100  of H2O  √ ½           
                                                        34
        2. Mass = (34 – 27) √ ½
                    = 7g of KCl √ ½
      3. When two solids are separately heated √ ½ and the gas passed over lime water, √ ½ white precipitate is formed √ ½  with sodium hydrogen carbonate while sodium carbonate does not produce a gas which turns lime water √ ½ into a white precipitate.
      4. Effevescences are seen in test tube with √ ½ water and no effervescence are seen in test tube √ ½ with methylbenzene. Water can react with magnesium to form hydrogen gas due to hydrogen ions √ ½  in water while methylbenzene is non – polar √ ½ hence lack ions.
      5.  
        1. B; √ ½ requires less volume √ ½ of soap to form lather and the volume of soap used does not change even  after boiling.
        2. Sample C contains temporary hardness √ ½ which is removed through boiling √ ½ hence reduction in volume of soap.
    3.  
      1.  
        1. 2HCl(aq) + Ca(HCO3)2(aq) → CaCl2(aq) + 2H2O(l) + 2CO2(g)      √1
        2. 12.0 × 0.05 = 0.0006 moles √ ½                       1
               1000
        3. 0.0006 √ ½ = 0.0003moles√ ½                       1
              2
      2.  
        1.  
          1. Hydrogen sulphide √1
          2. Sulphur (IV) oxide √1
        2. Pressure of 2-3 atmosheres √ ½
          Temperature of 450°c
        3. Sulphur obtained from sulphur (IV) oxide is added to carbon (IV) sulphide in a boiling tube. The contents is then stirred and filtered √ ½ into a dry beaker. The filtrate is allowed to evaporate √ ½ to form Rhombic sulphur.                                                            2
        4. When sulphur (IV) oxide is dissolved in water; excessive heat is generated that boil the acid to produce fine droplets that can cause burn. √1    1
        5. Ca(OH)2(aq) + SO2(g) → CaSO3(s) + H2O(l)
        6.  
          • Large scale manufacture of sulphuric (VI) acid √ 1
          • Vulcanisation
          • manufacture of bleaching agents
          • Used as a fungicide.
          • Manufacture of fireworks and dyes
    4.  
      1. H            H    H                                     H    H    H   H
        |              |       |                                      |      |      |     |
        C = C – C – C – H  + H – HScreenshot 2023 05 31 at 09.33.19   H – C – C – C – C – H
        |       |      |      |                                        |      |      |      |
        H     H    H    H                                      H    H    H    H
        (C=C) + 2( C-C ) + 8 ( C – H ) + H – H Screenshot 2023 05 31 at 09.33.193( C – C ) + 10 ( C – H )
        612 + 2 x 347 + 8 x 413 Screenshot 2023 05 31 at 09.33.193 x 347 + 10 x 413
        612 + 694 +3304+ 436              1041 + 4130
                                 5046 √1 Screenshot 2023 05 31 at 09.33.19 5171 √1
                               ∆H = -125KJmol-   √1                     3
      2.  
        1. 2CH3CH2CH2OH(l) + 9O2(g) → 6CO2(g) + 8H2O(l).   √1
        2. If 60g of C3H7OH Screenshot 2023 05 31 at 09.33.191560KJ
             10g of C3H7OH  Screenshot 2023 05 31 at 09.33.19 10 × 1560           √1
                                                            60
                           = 260KJ √1
      3.  
        1. The energy changes in converting reactants to products is the same regardless of the route by which the chemical change occurs. √1
        2.  
          1. Standard enthalpy changes. √1
          2. 3C(s) + 4H2(g) → C3H8(g) 

          3. Screenshot 2023 05 31 at 15.53.48
            ΔHθf(C3H8) = 3ΔHθc(c) + 4ΔHθc(H2)) − ΔHθc(C3H8)
                              = ( 3 x – 393 + 4 x – 287) – ( − 2209) √1
                              =( - 1179 + - 1148) + 2209
                              = - 2327 + 2209
                             = - 118Kjmol-1   √1
    5.  
      1.  
        1. NH4Cl/ Ammonium chloride √1
        2. PbCO3 (g) / Lead carbonate   √1
        3. Pb(NO3)2 (aq) / Lead nitrate  √1
      2. Heat √1
      3. Orange solid that cools to form a yellow solid √1
      4.  
        1. PbOs + 2HNO3(aq) → Pb(NO3)2 + H2O(l)     √1
        2.  
      5.  
        1. Name : Plumbate ion.  √1
        2. Formula : (Pb(OH)4)2- √1
      6. Mixture K is made of both soluble and insoluble salts hence need to separate them. √1
    6.  
      1.  
        1. CO2 is collected by downward delivery.  ✓1mk
        2. Exchange apparatus containing water and concentrated sulphuric (IV) acid.   ✓1
        3. Use dilute hydrochloric acid for dilute sulphuric acid    ✓
      2.  
        • It does not support combustion ✓1
        •  It is denser than air.    ✓1
      3.  
        1.  
          1. M-Ammonia gas.     ✓1/2
          2. Q-carbon (iv) oxide         ✓1/2
        2.  
          1. F-Ammonium chloride  ✓1/2
          2. X-Sodium hydrogen carbonate.   ✓1/2
        3.  
          • L-Calcium chloride ✓1
          • Used as a drying agent   ✓1
        4.  
          1. Tower;  P-NH3(aq)+CO2(g)+NaCl(aq)+H2O(l)  Screenshot 2023 05 31 at 09.33.19NaHCO3(s)+NH4Cl(aq) ✓1
          2. Chamber;  K  2NH4Cl(aq)  + Ca(OH)2(aq)  Screenshot 2023 05 31 at 09.33.19CaCl2(aq) + 2NH3(g) + H2O(l)  ✓1
        5.  
          • Sodium chloride. ✓1,
          • Ammonia, coke or limestone. ✓1
    7.  
      1. Due to production of CO2 which escape to the atmosphere  1
      2. CaCO3(s) + 2HCl(aq)  → CaCl2(aq) + H2O(l) + CO2(g)      1
      3.  
        • Grind marble chips to powder form 1
        • Increase concentration of HCl 1
        • Increase the temperature of the reactants                        any 2 correct = 2mks
      4. The reaction is complete since calcium carbonate has been used up 1
      5. White precipitate ½ insoluble ½ in excess ammonia solution
      6.  
        • global warming
        • cause acid rain                                                                               any one = 1mk
      7.   
        ChemSRF42023PrMP2Ans7
      8.  
        1. Favours forward reaction1orange colour intensify ✓1 concentration of hydrogen ions increases ✓1
        2. Favour backward reaction yellow colour formed✓1  the reaction produces heat/ exothermic✓1
    Read 381 times Last modified on Monday, 05 June 2023 07:11

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