Chemistry Paper 3 Questions and Answers with confidential - Kapsabet Mock Exams 2023

• Answer all the questions in the spaces provided.
• Mathematical tables and electronic calculators may be used.
• All working MUST be clearly shown where necessary.
• Use the first 15minutes of the 2 ¼ hours to ascertain you have all the chemicals and apparatus tha you may need.

QUESTION 1

• You are provided with solution K and L
• Solution K is 1M H₂SO₄
• Solution L contains 8.7g of the hydroxide of metal M {with formulae MOH] in 600cm³ of the solution
• You are required to carry out the experiment to determine;
  1. Concentration of solution L
  2. R.A.M of metal M

Procedure

1. Measure 75cm³ of solution K and put into a clean 250cm³ volumetric flask and add distilled water up to the mark
   -label this solution W
2. Fill a clean burette with solution W
3. Pipette 25cm³ of solution L into a clean conical flask and add 2 drops of phenolphthalein indicator
4. Titrate the solution W in the burette against solution L in the conical flask and record the results in the table below
5. Repeat {3} and {4} above as you fill the table below.

TABLE 1

1. Calculate the;
   1. Average volume of solution W used                                                                            [1mk]
   2. Concentration of solution W                                                                                         [1mk]
   3. Number of moles of solution W that reacted with each 25cm³ portion of solution L  {2mks]
2. Calculate the;
   1. Number of moles of the metal hydroxide {MOH} in solution L that reacted with each portion of solution W   [2mks]       
   2. Concentration of solution L               [1mk]
   3. Number of moles of the metal hydroxide [MOH]in 600cm³ of solution L               [2mks]
   4. R.A.M of metal M                [2mks]
      [0=16, H=1]

QUESTION 2

You are provided with solution N and P

• Solution N is 2M HCl
• Solution P is 0.16M sodium thiosulphate
• You are required to carry out the experiment below to determine how concentration affects the rate of reaction between HCl and sodium thiosulphate solutions

PROCEDURE

1. Fill a clean burette with solution P.
   Measure 25cm³ of the solution P from the burette into a clean 100cm³ glass beaker and place on a white piece of paper with a cross[x]  marked on it
2. Add 10cm³ of solution N into it and immediately start a stop watch and note the time taken for the cross beneath the mixture to become invisible
3. Clean the 100cm³ beaker and measure into it 20cm³ of solution P form the burette, and add 5cm³ of distilled water into the solution solution
4. Repeat step [2] above and note  the time taken for the cross to become invisible
5. Repeat  the experiment using volumes indicated on the table below and as you record  the results

TABLE 2

1. Plot a graph of 1t against volume of solution P on the grid provided                                 [3mk]
2.  From the graph
   1. Determine the time taken for the cross to become invisible when 12.5cm³ of solution P is used            [2mks]
   2. Explain the effect of concentration on the rate of reaction between HCl and sodium thiosulphate solution    [2mks]         

QUESTION 3

• You are provided with solids Q and R
• You are required to carry out the tests below as you record your observations and inferences

(i) SOLID Q

-Add about 5cm³ of distilled water to solid Q, shake the mixture thoroughly for a while and then filter it
NOTE: Retain both the filtrate and the residue for the tests below

{ii}SOLID R

                                                                                      CONFIDENTIAL

1. Each student should be supplied with the following
   1. Burette
   2. Pipette
   3. Pipette filler
   4. Filter funnel
   5. White tile
   6. Clamp and stand
   7. 2 conical flask
   8. 100 cm³ glass Beaker (empty)
   9. Stop watch
   10. 100cm³ measuring cylinder
   11. 10cm³ measuring cylinder
   12. 250 cm³ volumetric flask
   13. Metallic spatula
   14. 6 clean test tubes
   15. Test tube holder
   16. 500ml distilled water
   17. White piece of paper or filter paper
   18. 1 filter paper
   19. 1 labelling paper
   20. Phenolphthalein indicator
   21. About 90cm³ solution K
   22. About 100cm³ solution L
   23. About 70cm³ solution N
   24. About 90cm³ solution P
   25. About 0.5gNaHCO₃
   26. About 1.0g solid Q
   27. About 0.5g solid R
2. Each student should have access to the following solutions:
   1. Means of heating
   2. 2M NaOH
   3. 2M HNO₃
   4. Pb(NO₃)
   5. Acidified KMNO₄
   6. Potassium iodide solution
      NB: the above solutions should be supplied with a dropper each.
3. SOLUTIONS PREPARATION AND SOLID MEASUREMENTS
   1. SOLUTION K IS 1M H₂SO₄
   2. SOLUTION L IS 0.36 M NaOH CONTAINING 14.4g OF NAOH IN 1 LITRE OF THE SOLUTION
   3. SOLUTION N IS 2M HCl
   4. SOLUTION P IS 0.16 M Na₂S₂O₃(SODIUM THIOSULPHATE)
   5. SOLID Q IS A MIXTURE OF SODIUM SULPHITE(Na₂SO₃) AND LEAD (II) CARBONATE (PbCO₃) MIXED IN THE RATIO 1:1 (should be thoroughly mixed)
   6. SOLID R IS MALEIC ACID

                                                                               MARKING SCHEME

QUESTION 1
TABLE 1

• complete table CT  1 mk
• decimal point D 1 mk
• accuracy A (tied to school value)1 mk
• principal of averaging 1 mk
  1.  
     1. Average volume / final accuracy 1(tied to school value)
        NB theoretically expected value = 15.0 cm³
     2. 1M x 75 cm³  ½ mk
            250 cm³
                                = 0.3M            ½ mk
        Ans in ii) above    X ans in (a) above ½ mk = ans ½ mk
                                1000
  2.  
     1. 2MOH_(aq) + H₂SO4 _(aq)      →      M₂SO_{4 (aq)} + H₂O_(l)   1mk
        Mole ratio = 2:1   ½ mk
        Moles of solution W = 2 x ans in a(iii)   ½ mk
     2. ans in b(i) x 1000 ½ mk  = ans ½mk
                     25
     3. ans in (i) ix 600 ½ mk = ans ½ mk
                    25
     4.       8.7        ½ mk = RFM OF MOH½ mk
        ans in b (iii)
        
     5. RAM of metal M = RFM  -(16+1) ½ mk= ans½ mk

QUESTION 2 
TABLE 2 

• complete table CT 1mk
• decimal point D 1mk
• trend (increasing time) 1mk
• 1/t row completed 1mk
  1. Graph
     • Plotting 1mk
     • Scale 1mk
     • Straight line touching origin (0,0)  1mk
  2.  Correctly read value from the graph  1mk
  3. Correct reciprocal of value read from the graph  1mk
  4. Rate at reaction increase with increase in concentration of the sodium thiosulphate because increase in concentration increases number of successful collisions

Question 3

(i) Solid Q 

(ii) Solid R