Chemistry Paper 3 Questions and Answers - Kakamega Evaluation Mock Exams 2022

QUESTIONS

1. You are provided with :-
   • Sulphuric (VI) acid, solution P
   • 0.25M sodium hydroxide, solution S
   • Solid R
     You are required to determine the concentration of sulphuric (VI) acid in moles per litre
     PROCEDURE I
     Using a burette, place 50.0cm³ of sulphuric (VI) acid, solution P in a 100ml beaker. Measure the temperature of the solution after every half – minute and record the values in table 1. At exactly 1 ½ minute, add solid R to the acid. Stir the mixture gently with the thermometer ensuring the solid  is intact in  the solution  and note the temperature of the mixture after every half – minute and record the values in table 1.
     
     1. Table 1
        

        Time (minute)	0	½	1	1½	2	2½	3	3½	4	4½	5	5½	6
        Temperature (ºC)

     2.      
        1. Plot a graph of temperature ( y – axis) against time. (3mks)
        2. Using the graph, determine the highest change in temperature. (1mk)
        3. Calculate the heat change for  the reaction (Assume that the specific heat capacity of the mixture is 4.2Jg-1 k-1 and density of the mixture is 1g/ cm)³. (2mks)
        4. Given that the molar heat of reaction of sulphuric (VI) acid with solid R is 320 kJ mol-1, calculate the number of moles of sulphuric acid that were used during the reaction. (2mks)
           PROCEDURE II
           Transfer ALL the contents of the 100 ml beaker  used in procedure I into a 250ml volumetric flask. Add distilled water to make up to the mark. Label this solution Q.
           Rinse the burette and fill it with sodium hydroxide, solution S
           Using a pipette and a pipette filler, place 25.0 cm³ of solution Q into a 250ml conical flask. Add two or three drops of phenolphthalein indicator and titrate against sodium hydroxide. Record your results in table 2. Repeat the titration two more times and complete table 2.
           Table 2
           

           Experiment	I	II	III
           Final burette reading (cm3)
           Initial burette reading  (cm3)
           Volume of solution S used (cm3)

           (4mks)
           1. Calculate the :-
              1. Average volume of solution S used.
              2. the number of moles of sodium hydroxide used.
              3. Sulphuric (VI) acid in 25cm³ of solution Q (1mk)
              4. Sulphuric (VI) acid in 250cm³ of solution Q. (1mk)
           2. Calculate the number of moles of sulphuric (VI) in 50cm³ of solution P.
           3. Calculate the concentration of the original sulphuric (VI) acid solution P in moles per litre (2mks)
2. You are provided with solution Q.  Carry out the tests shown below and answer the questions that follow. 
   1. Dip a clean glass rod in solution Q provided and heat it using a non-luminous flame.  
      

      Observations	Inferences
      (1 mark)	( 1mark)

      Divide the above solution Q into four portions
   2. To about 1cm³ of the solution add 2M sodium hydroxide dropwise until excess.
      

      Observations	Inferences
      (1 mark)	( 1mark)

   3. To the second portion add 2M ammonia solution dropwise until excess. 
      

      Observations	Inferences
      (1 mark)	( 1mark)

   4. To 1cm³ of solution Q add a few drops of Lead (II) nitrate solution.
      

      Observations	Inferences
      (1 mark)	( 1mark)

   5. To 1cm³ of solution Q add four drops of barium nitrate solution followed by a few drops of 2M nitric (V) acid. 
      

      Observations	Inferences
      (1 mark)	( 1mark)

3. You are provided with substance E. Carry out tests on it.
   1.        
      1. Place about one third of solid E on a metallic spatula and ignite it in a flame.
         

         Observations	Inferences
         (1 mark)	( 1mark)

         Place the remaining solid E boiling tube and add about 5cm³ of distilled water. Shake the contents and divide into 3 portions.
      2. To portion one add 3 drops of Universal indicator
         

         Observations	Inferences
         (1 mark)	( 1mark)

   2. To the second portion add all the sodium carbonate provided
      

      Observations	Inferences
      (1 mark)	( 1mark)

   3. To third portion add 2 drops of acidified potassium manganate (VII) solution. Warm the mixture
      

      Observations	Inferences
      (1 mark)	( 1mark)

CONFIDENTIAL
In addition to the apparatus and the fitting found in a chemistry laboratory, each candidate will required the following

1. About 70cm³ of solution P.
2. About 80cm³ of solution S
3. Exactly 7.5 cm solid R (May be fold twice)
4. One thermometer -10ºC - 110ºC
5. One stop watch / clock
6. One 100ml plastic beaker
7. One burette 0 – 50ml
8. One pipette 25ml and a pipette filler
9. One volumetric flask 250 ml
10. About 500cm³ of distilled water supplied in a wash bottle 
11. One label  
12. Two conical flasks
13. 10ml measuring cylinder
14. Five clean dry test – tube in a test tube rack.
15. Glass rod
16. One boiling tube
17. One spatula
18. One test – tube holder
19. Filter funnel
20. PH chart
21. 5ml of solution Q
22. About 0.5g of anhydrous sodium carbonate
23. About 0.5g of solid E

Access to:

1. Bunsen burner
2. 2M sodium hydroxide provided with a dropper
3. Phenolphthalein indicator supplied with a dropper
4. Lead (II) nitrate solution supplied with a dropper
5. Barium nitrate solution supplied with a dropper
6. 2M aqueous ammonia
7. Universal indicator solution
8. Acidified potassium manganate (VII)
9. 2M Nitric (V) acid

NOTE

1. Solution P  is prepared by adding exactly 27.2 cm³ of concentrated sulphuric (VI) acid of specific gravity ( density) 1.84g / cm³ to about 600cm³ of distilled water and diluting  to one litre of solution
2. Sodium hydroxide is prepared by dissolving exactly 10g of sodium pellets in about 800cm³ of distilled water and diluting to one litre of solution
3. Solid R is exctaly 7.5cm magnesium ribbon
4. Lead (II) Nitrate solution is prepared by dissolving 33.1g  of lead (II) Nitrate solid to 1 litre of distilled water
5. Barium Nitrate solution is prepared by dissolving 26.1g of Barium Nitrate in 1 litre of distilled water.
6. Solution Q made by mixing sodium sulphate and zinc sulphate in the ratio of 1:1 and dissolving in 10ml of distilled water
7. 2M Nitric (V) acid is  prepared by dissolving 134cm³ of concentrated Nitric (V) acid of specific gravity 1.42 g/cm³ to about 600cm³ of distilled and diluting to 1 litre of solution
8. 2M sodium hydroxide solution is prepared by dissolving 80g of sodium hydroxide pellets to about 800cm3 of distilled water and diluting to 1 litre of solution
9. Solution Y -Acidified Potassium Manganate (VII)prepared by dissolving 9g of solid Potassium Manganate (VII) in about 600cm³ of 2M Sulphuric (VI) acid and adding distilled water to make a litre of solution.
10. Solid E is oxalic acid

MARKING SCHEME

1.        
   1. CT = Complete table ….1mk
      Table to be filled completely
      If at time 0min a student records temperature as 0 or any reading is more than 40 penalize half mark.
      D.P = decimal point ……. ½mk
      All values to be recorded as whole numbers OR with a decimal as 0 or 0.5 only if any other figure is used award 0mk for d.p
      Accuracy.Consider reading at time 0min if  +/- 2oC of school value award ½mk, if beyond award 0mk
      Trend 1 mk
      For time t= 0to 1½  values to be constant. ½ mk
      For time t = 2 ½ to 6 ½mk
      Values to be rise and be higher than those of t = 0 to t = 1 ½ .the last values to drop 
   2. Graph
      
      Labeled axes …. ½mk
      Axes to be labeled with quantities 
      Scale ………….½mk
      Plot to cover ¾ of the given grid.
      Plots …………..1mk
      To be plotted accurately, 10-12 (1mk), 9plots (½ mk)
      Plots for t =0 to 1 ½ to be joined by straight line …. ½mk. Draw line for drop and extrapolate ½mk
      1. ½ mk for using graph ( must show dotted line on graph or blocked liner)
         ½ mk for correct answer
         If not shown in graphs penalize fully.
      2. MCΔT
         M ≡ 50 x 1.0g/cm³ = 50g ½  mk
         = 50 x 4.2 x higher of ans b(ii) //  50 x 4.2 xΔt 1mk
         = ans ½  mk
         Penalize ½ mk for omitting units or wrong units in final answer
         Accept J or kJ units
      3. Value obtain in b(iii) 
                  320
         Procedure II
         Table 2
         CT – 1mk
         Decimal – 1mk
         Accuracy – 1mk
         Principle of averaging – 1mk
         Final answer – 1mk
         1.      
            1. I : ans a(i)  x 0.25 ½ mk      = ans ½ mk  
                           1000
            2. Moles ratio between H₂SO₄ and NaOH = 1 : 2// ½ mk
               Moles of H₂SO₄in 25cm³ = ½ x ans a(ii)  
               = ans ½ mk
            3. ans a(iii) x 250 ½ mk   = ans
                  25
         2. Moles of procedure I b(iv)  + procedure II a(iv) 
         3. Ans part (d)  x 1000
                        50
2. Observation Inference 
   

   Observations	Inferences
   Yellow flame  1mk  Whit ppt. forms ½mk  soluble in excess ½mk   Whit ppt. ½mk  soluble in excess ½mk  White ppt  1mk  white ppt  ½mk insoluble in the acid ½mk	Na+  present   1mk Zn2+  ,  Al3+ ,  Pb2+   present Zn2+  present SO42-, CO32- , SO32-, CI-    present SO42-   1mk

3. Observation Inference 
   

   Observations	Inferences
   Burns with sooty yellow flame pH = 4 - 6 Bubbles evolved // Effervescence purple KMnO4decolourized	unsaturated organic compound // Weakly acidic (½mk) –COOH present  (½mk) R - OH   ½ mk