Chemistry Paper 3 Questions - Maseno Mock Examinations 2022

QUESTIONS

1. You are provided with:
   
   • Solution A, 2M Hydrochloric acid
   • Solution B; 0.15 sodium Thiosulphate
   • Solution C; Sodium Carbonate
     Procedure 1
     Measure 20cm³ of 0.15M Sodium thiosulphate (Solution B) into a 250cm³ conical flask. Place the beaker on a white piece of paper with the ink mark ‘X’ on it. Measure 20cm³ of 2M Hydrochloric acid (Solution A) using a 50cm³ measuring cylinder. Put the acid into the conical flask containing sodium thiosulphate and immediately start off the stop watch. Determine the time taken for the mark ‘X’ to become invisible/obscured when viewed from above. Repeat the procedure by measuring different volumes of the acid and adding the volumes of the distilled water to complete Table I below.
     Table I
     

     Volume of acid (cm3)	Volume of water (cm3)	Volume of sodium thiosulphate (cm3)	Time taken for mark X to be invisible(seconds)	Reciprocal of time (sec-1)1/t
     20	0	20
     18	2	20
     16	4	20
     14	6	20
     12	8	20
     10	10	20

     1. Complete the table above. (6 marks)
     2. Plot a graph of 1/t (rate of reaction) against volume of acid used. (3marks)
     3. Explain the shape of the graph. (1 mark)
     4. From the graph determine
        
        1. Time taken for the cross (X) to be obscured/invisible when the volume of the acid is
           
           1. 15cm³ (1mark)
           2. 8cm³ (1 mark)
        2. The volume of the acid used if the time taken for the cross (x) to be obscured/invisible is:
           
           1. 40 seconds (1 mark)
           2. 43 seconds
              Procedure 2
              Using a 10cm³ measuring cylinder, place 10cm³ of solution A into 250ml volumetric flask. Add about 200cm³ of distilled water, shake well. Add more distilled water to top up to the mark. Label this solution D. fill the burette with solution D using a pipette and pipette filter, pipette 25cm³ of solution C into a conical flask. Add 3 drops of phenothalene indicator and titrate with solution D
              Record your results in the table 2. Repeat the titration two more times and complete table 2.
              Table 2
              

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

              (4 marks)
              1. Determine the
                 1. Average volume D used (1 mark)
                 2. Moles of the acid in the average volume of solution D used. (2marks)
                 3. Concentration of solution C in the moles per liter. (2 marks)
2. You are provided with solid E. carry out the following tests and record the observation and inferences in the spaces provided.
   
   1. Place about one third of solid E in a dry test-tube. Heat the solid strongly and test any gas produced with both blue and red litmus papers.
      

      Observations	Inferences

   2. Place the remaining amount of solid E in a boiling tube. Add about 15cm³ of distilled water and shake. Divide the mixture into four test-tubes each containing about 2cm³
      
      1. To the first portion, add three or four drops of dilute hydrochloric acid.
         

         Observations	Inferences

      2. To the second portion, add two or three drops of aqueous barium nitrate.
         

         Observations	Inferences

      3. To the third portion add aqueous sodium hydroxide drop wise until in excess.
         

         Observations	Inferences

      4. To the fourth portion, add aqueous ammonia drop wise until in excess
         

         Observations	Inferences

3. You are provided with solid F. Carry out the test below and record your observations and inferences in the spaces provided.
   
   1. Place one third on a metallic spatula. Burn it in a non-luminous flame of the Bunsen burner.
      

      Observations	Inferences

   2. Place the remaining solid F in a boiling tube. Add about 10cm³ of distilled water and shake the mixture well. Retain the solution for the next procedure.
      

      Observations	Inferences

   3. To about 2cm³ of the solution, add 2 drops of acidified potassium manganate(VII) and warm.
      

      Observations	Inferences

   4. To about 2cm³ of the solution, add 3 drops of acidified potassium dichromate (VI) and warm.
      

      Observations	Inferences

   5. To about 2cm³ of the solution. Add 0.5g of sodium hydrogen carbonate.
      

      Observations	Inferences

CONFIDENTIAL
INSTRUCTIONS
Apart from the usual laboratory fittings, each students should have following:

1. 100cm³ of solution A
2. 100cm³ of solution B
3. 100cm³ of solution C
4. About 0.5g of solid E
5. About 0.5g of solid F
6. Distilled water in 500ml wash bottle
7. 2 labels (2)
8. Spatula (metallic spatula)1
9. 50ml measuring cylinder
10. 10ml measuring cylinder
11. One burette 0-50ml
12. One pipette 25ml
13. 2-250 conical flask
14. One 250ml volumetric flask
15. Blue and red litmus paper
16. Stop watch
17. Phenophthalene indicator
18. Two boiling tubes
19. 6- dry test-tubes in a rack
20. Test-tube holder
21. 0.5g of solid sodium hydrogen carbonate
22. Pipette filler
23. White piece of paper
24. Filter funnel

Access to:

• 2M NaOH_(aq)
• 2M NH_3(aq)
• 2M HCl_(aq)
• 0.5M Ba (NO₃)_2(aq) with dropper
• KMnO₄│H+ supplied with dropper
• K₂Cr₂O₇│H+

NOTES:

1. Solution A is prepared by weighing exactly 172cm³ of hydrochloric acid (35-37% sp. Gr 1.184)
2. Solution B is prepared by weighing exactly 372g of Sodium thiosulphate pentahydrate and dissolving to make 1dm³ of solution
3. Solution C is prepared by weighing exactly 4.8g of sodium carbonate dissolve t to make 1dm³ of solution.
4. Solid E is Hydrated Ammonim Aluminiun sulphate
5. Solid F is maleic acid.