Chemistry Paper 3 Questions and Answers with Confidential - Form 4 Mid Term 2 Exams 2021

CHEMISTRY
PAPER 3
FORM 4 MID TERM 2

INSTRUCTIONS

• Answer all questions

1. QUESTION 1
   You are provided with:
   • Solution Q 0.125M Hydrochloric acid solution
   • N grammes of anhydrous sodium carbonate.
   • Methylorange indicator
     You are required to prepare a solution of sodium carbonate and then standardize it with hydrochloric acid solution Q.
     
     Procedure
   • Transfer all the N grams of sodium carbonate into a 250 ml volumetric flask.
   • Add 100cm3 of distilled water and shake till all the solid dissolves.
   • Add more distilled water upto the 250 ml mark and label it solution P. using a measuring cylinder, transfer 50cm3 of solution P into a clean 250 ml beaker and add 50cm3 of distilled water.
   • Stir well with a glass rod and label it solution T.
   • pipette 25.0cm3 of solution T and place it into a conical flask, add 2 drops of methyl orange indicator and titrate with solution Q from the burette. Record your results in the table 1 below and repeat the titration part to complete the table below.
     (3 mks)
     

     	I	II	III
     Final burette reading (cm3)
     Initial burette reading (cm3)
     Volume of Q used (cm3)

     
     
     1. Calculate the average volume of solution Q used. (1 mk)
     2.    
        1. Calculate the number of moles of solution Q used. (2 mks)
        2. Write an equation for the reaction between solution T and Q. (1 mk)
           Calculate:
        3. Number of moles of sodium carbonate solution in 25cm3 of solution T. (2 mks)
        4. Number of moles of sodium carbonate in 100cm3 of solution T. (2 mks)
        5. Number of moles of sodium carbonate in 50cm3 of the original solution P. (2 mks)
     3. Given that Na=23.0, C=12.0, O=16.0;
        1. The mass of sodium carbonate N grammes that were dissolved to make solution P. (1 mk)
        2. The concentration of sodium carbonate solution P in moles per litre. (2 mks)
2. QUESTION 2
   You are provided with:
   • 1 M Sulphuric (vi) acid solution D.
   • 2 M Sodium hydroxide solution C.
     You are required to determine the heat of neutralization of Sulphuric (vi) acid solution D.
     
     Procedure
   • Measure 50cm3 of solution C and transfer into a 250cm3 plastic beaker provided. record the initial temperature of solution C.
   • measure 10cm3 of sulphuric(vi)acid solution D and add it to solution C in the beaker. Stir gently with the thermometer to mix and record the highest temperature in the table below.
   • Continue adding 10cm3 portions of solution D recording the temperature after each addition until 80cm3 of solution D has been added. (3 mks)
     

     Total volume of solution D added (cm3)	0	10	20	30	40	50	60	70	80
     Temperature of the mixture (ºC)

     
     
     1. Plot a graph of temperature against volume of sulphuric(vi)acid solution D added. (3 mks)
     2. From your graph determine the maximum temperature change ΔT. (1/2 mk)
     3. From your graph determine the volume of sulphuric(vi)acid solution required for neutralization.(1/2 mk)
     4. Calculate the molar heat of neutralization of 1M sulphuric(vi)acid solution D. (Assume density of water = 1g/cm3, specific heat capacity = 4.2 Jg-1K-1) (3 mks)
3.                
   1. You are provided with solid A. carry out the following tests, record the observations and inferences.
      1. Place solid A in a boiling tube and add about 10cm3 of distilled water while shaking. Filter the solution and divide the filtrate into three portions. Keep the residue for part (b).
         

         Observation	Inference

         
         
         1. To the first portion, add sodium hydroxide dropwise till in excess.
            

            Observation	Inference

         2. To the second portion add 3 drops of barium nitrate solution.
            

            Observation	Inference

         3. To the third portion add 3 drops of lead(ii)Nitrate solution
            

            Observation	Inference

      2. Place the residue in(a) above in a boiling tube. Add dilute nitric(v)acid while shaking till the solid just dissolves.Divide the solution into two portions.
         

         Observation	Inference

         1. To the first portion add sodium hydroxide solution dropwise till in excess.
            

            Observation	Inference

         2. To the second portion, add a few drops of ammonia solution then in excess.
            

            Observation	Inference

   2. You are provided with solid Z. carry out the tests below and record your observations and inferences. Place all of solid Z into a boiling tube. Add 10cm3 of distilled water and shake well. Divide the solution into three portions. 
      1. Test the first portion with both blue and red litmus paper.
         

         Observation	Inference

      2. To the second portion add 2 drops of acidified potassium manganate(vii) and shake well.
         

         Observation	Inference

      3. To the third portion add a little sodium hydrogen carbonate.
         

         Observation	Inference

CONFIDENTIAL

In addition to the other common apparatus and reagents found in a chemistry laboratory, each candidate will require the following.

1. About 100cm³ of 0.125M Hydrochloric acid labelled solution Q.
2. Accurately weighed 2.65g of unhydrous sodium carbonate labeled solid N.
3. 250ml volumetric flask.
4. 100ml measuring cylinder.
5. Distilled water
6. 250 ml empty glass beaker
7. Glass rod
8. 1 label
9. One burette (0-50ml)
10. One 25.0 ml pipette
11. Two conical flasks (250 ml)
12. Methyl orange indicator
13. Retort stand
14. Pipette filler
15. A white tile
16. 6 dry test tubes
17. 1 boiling tub
18. One filter funnel
19. 0-1100C thermometer
20. 1 metallic spatula
21. About 60cm³ of 1M Sulphuric(vi)acid labeled solution D.
22. About 60cm³ of 2M sodium hydroxide solution labeled solution C.
23. 250 ml plastic beaker empty.
24. About 0.5g of solid Z.
25. About 1.5g of solid A.
26. 1 red and 1 blue litmus paper.
27. About 0.2g of sodium hydrogen carbonate.
28. 1 filter paper.

Access to:

1. 2M NaOH with a dropper.
2. 2M Ammonia solution with a dropper.
3. 0.25M Barium nitrate solution with a dropper.
4. 0.2M Lead (ii) nitrate solution with a dropper.
5. 0.02M acidified Potassium Manganate (vii) with a dropper.
6. 1M Nitric(v) acid.

NOTE:

1. Solid A is a mixture of zinc carbonate and Sodium Sulphate in the ratio 1:1.
2. Solid Z is oxalic acid.
3. Solution Q is 0.125M Hydrochloric acid prepared by dissolving 10.75cm3 of concentrated hydrochloric acid in 1 litre.
4. Solution D is 1M Sulphuric (vi) acid prepared by dissolving 55 cm³ of concentrated sulphuric (vi) acid in 1 litre of solution (Density of Sulphuric acid is 1.84 g/cm³).
5. Solution C is 2M sodium hydroxide prepared by dissolving 80g of sodium hydroxide pellets in 1 litre of solution.
6. 2 M Ammonia solution is prepared by dissolving 112cm³ of concentrated ammonia solution in 1 litre of solution.
7. 0.25M Barium nitrate is prepared by dissolving 65g of Barium nitrate in 1 litre of solution.
8. 0.2M lead(ii)nitrate is prepared by dissolving 66.2g of lead(ii)nitrate in a litre of solution.
9.  1 M nitric acid is prepared by dissolving 64cm³ of concentrated Nitric(v) acid in 1 litre of solution.
10. 0.02M acidified potassium manganate(vii) is prepared by dissolving 3.2g of the solid in 2.00cm³ of 2M sulphuric(vi) acid then diluting to 1 litre.

MARKING SCHEME

1.    
   Table:
   • Award 1 mark for 3 titrations
   • Award 1/2 mark for only 2 titrations
   • Award 0 mk for 1 titration done
   • Decimal - 1mk
   • Accuracy 1mk 
     ± 0.2cm³ award ¹/₂ mk
     ± o.1cm³ award 1mk
     Total 3 mks
     1. Average volume of solution Q= 20.0cm3
     2.     
        1. moles of solution Q used
           20 x 0.125 = 0.0025 moles
              1000
        2. Na₂CO_3(s) + 2HCl_(aq) → 2NaCl_(aq) + CO_2(g) + H₂O_(l)
        3. Moles of Na2CO3 in 25cm³ of solution T 
           ¹/₂ x 0.0025 = 0.00125
        4. Moles of Na₂CO₃ in 100cm³ of solution T
           25cm³ → 0.00125moles
           then 100cm³ = 0.00125 x 100 = 0.005 moles
                                         25
        5. Moles of Na2CO3 in 50cm3 of the original solution P
           0.00moles → 100cm³ of T
                           → 250cm³
           250 x 0.005=0.025
              50
        6.     
        7. Mass of Na₂CO₃ in grammes
           =0.025 x 106g= 2.65g
        8. Concentration of Na₂CO₃ in solution P
           2.65 →250cm³
             ? → 1000cm³
           2.65 x 1000 = 10.6g/litre
              250
           Molarity= ^10.6/₁₀₆ = 0.1m
2.  
     

   Total volume of solution D added (cm3)	0	10	20	30	40	50	60	70	80
   Temperature of the mixture (ºC)	240.	30.0	33.0	36.0	37.0	35.0	34.0	33.0	31.0

   
   CT 1 mk
   D.P - 1mk
   Temperature at 0 volume of solution D ± 2D
   1. Graph of temperature against volume of sulphuric (vi) acid added during neutralization reaction
      Labelled axis with units - 1mk
      plotting - 1mk
      Shape - 1mk
      Total - 3mks
   2. Temperature changes =- 13.0ºC
   3. Volume of H₂SO₄ required for neutralization 40cm³(1/2mk)
   4. Molar heat of neutralization
      Heat change= MCθ
      =(50 + 40) x 42 x 13J
      =90 x 42 x 13J= -4914J
      Moles of H₂SO₄ = 1 x 40= 0.04
                                   1000
      0.04 moles → -4914J
       1mole → ?
      -4.914 = 122.85KJ/mol
         0.04 
         
      
3.            
   1.     
      1.      
            

         Observation	Inference
         - White residue - Colourless filtrate	Cu2+, Fe2+, Fe3+ present

          
         1.  
            

            Observation	Inference
            No white ppt	Pb2+, Al 3+. Zn2+ absent  or K+ or Na+ present

               
         2.  
            

            Observation	Inference
            White ppt formed	SO42-, SO32-, CO32- present (any two)

               
         3.    
            

            Observation	Inference
            White ppt present	SO42- present

             
      2.    
         

         Observation	Inference
         Effervesence, produces colourless gas	CO32- present

          
         1.  
            

            Observation	Inference
            White ppt which dissolves in excess	Pb2+, Al3+, Zn2+ present

                
         2.    
            

            Observation	Inference
            White ppt that dissolves in excess	Zn2+ present

              
   2.        
      1.    
         

         Observation	Inference
         Blue litmus turns to red, red litmus remains red	H+ present

           
      2.    
         

         Observation	Inference
         Purple acidified potassium manganate (vii) is decolourised	|    | C = C  |     | -C≡C- or  R-OH present

      3.  
         

         Observation	Inference
         Effervesence present	H+ present