Chemistry Paper 3 Questions and Answers with Confidential - Lainaku II Joint Mock Examination 2023

Instructions:

• Answer ALL questions
• You are NOT allowed to start working with the apparatus for the first 15 minutes of the 2 ¼ hours allowed for this paper. This time will enable you read through the question paper and make sure you have all the chemicals and apparatus required.
• Mathematical tables and electronic calculators may be used
• All working must be clearly shown where necessary.

1.You are provided with:

• Solution A of Potassium manganate (VII).
• 0.05M solution B of oxalic acid.
• Solution C containing 4.9g of ammonium iron (II) Sulphate, (NH4)2 SO4.FeSO4.6H2O, in 250cm3 of water.
• You are required to:
  1. Determine the rate of reaction between oxalic acid and Potassium manganate (VII) solutions.
  2. Standardize the solution A.

PROCEDURE I:

1. Fill the burette with solution A.
2. Place 1 cm³ of solution A from the burette into each of the five (5) test-tubes in a test tube rack.
3. Using a clean measuring cylinder, place 19 cm³ of solution B into a boiling tube.
4. Place the thermometer into solution B and heat gently until it attains a temperature of 40°C.
5. Add the first portion of solution A immediately and at the same time start a stop watch.
6. Record the time taken for solution A to be decolorized in table I below.
7. Repeat the procedure (i) to (v) at temperatures of 50°C,60°C,70°C and 80°C to complete the table.

Table I

Temperature of solution B (oC)	40	50	60	70	80
Time taken for decolorization (seconds)
Rate ( I/t ) s-1 X 1000

                                                                                                              (4 marks)

1. Plot a graph of ( ¹/_t X 1000) against temperature (X-axis) (3 marks)
2. From the graph determine the time taken for the mixture to decolourise at 65°C (2 marks)
3. How does the rate of reaction between oxalic acid solution B and Potassium manganate (VII) solution A vary with temperature? (1 mark)

PROCEDURE II

• Refill the burette with solution A.
• Pipette 25cm³ of solution C into a conical flask and titrate the solution A against solution C until a permanent pink colour just appears.
• Record your results in table II below and repeat the procedure to fill the table.
  Table II
  

  	1	2	3
  Final burette reading (cm3)
  Initial burette reading (cm3)
  Volume of A used (cm3)

1. Determine the average volume of A used. (1 mark)
2. Calculate the concentration of solution C in moles per litre (Fe = 56, S = 32, O = 16, N =1 4, H = 1) (1 mark)
3. Find the number of moles of solution C used. (1 mark)
4. Given the ionic equation for the reaction is
   5Fe²⁺_(aq) + MnO_4⁻(aq) + 8H⁺_(aq) ⟶ 5Fe³⁺_(aq) + Mn²⁺_(aq) + 4H₂O_(l);
   Find the number of moles of solution A used. (1 mark)
5. Determine the concentration of the Potassium manganate (VII), solution A in moles per litre.  (2 marks)

2.You are provided with solid Q. Carry out the tests below and record your observations and inferences in the table below

1. Place half a Spatula full of solid Q in a clean dry test-tube and heat gently then Strongly.
   Test the gas produced using moist red and blue litmus papers
   

   Observations	Inferences
   (1 mark)	(1 mark)

2. Place the remaining solid Q in a boiling tube, add about 5cm3 of distilled water and shake well. Divide the resulting mixture into four portions for the tests below.
   

   Observations	Inferences
   (1 mark)	(1 mark)

   
   
   1. To the first portion add Sodium hydroxide solution dropwise until in excess.
      

      Observations	Inferences
      (1 mark)	(1 mark)

   2. To the second portion add 2-3 drops of dilute Sulphuric (VI) acid
      

      Observations	Inferences
      (1 mark)	(1 mark)

   3. To the third portion add aqueous ammonia dropwise until in excess
      

      Observations	Inferences
      (1 mark)	(1 mark)

   4. To the fourth portion add 2-3 drops acidified barium nitrate solution
      

      Observations	Inferences
      (1 mark)	(1 mark)

3.You are provided with solid L. carry out the tests below on L and record the observations and inferences in the spaces provided.

1. Place half of solid L in a boiling tube and add about 5cm3 of distilled water
   1. 
      

      Observations	Inferences
      (1 mark)	(1 mark)

      Divide the solution into two portions and carry out the tests below.
      
      
   2. To the first portion add 2-3 drops of acidified potassium manganate (VII).
      

      Observations	Inferences
      (1 mark)	(1 mark)

   3. To the second portion add Sodium carbonate provided.
      

      Observations	Inferences
      (1 mark)	(1 mark)

2. Place the remaining solid L in metallic spatula and ignite it.
   

   Observations	Inferences
   (1 mark)	(1 mark)

CONFIDENTIAL

1. Apart from the school laboratory fittings supply the following
   1. 100cm³ solution A - 0.02M Acidified potassium manganite (VII) (H⁺/KMnO₄)
   2. 100cm³ Solution B - 0.05M Oxalic acid
   3. 100cm³ Solution C - containing 4.9g of (NH₄)₂SO₄ FeSO₄.6H₂O in 250cm³ of solution)
   4. 50ml measuring cylinder
   5. 5 Test tubes
   6. 1 boiling tube
   7. 250ml beaker
   8. Thermometer
   9. Stopwatch
   10. Burette
   11. Pipette
   12. Two conical flasks
   13. About 0.5g of solid Q (ZnSO₄)
   14. Distilled water
   15. About 0.5g of solid L (oxalic acid)
   16. Red and blue litmus papers
   17. Metallic spatula
   18. test tube holder
   19. 0.5g sodium carbonate

ACCESS TO:

1. 1 M Sodium hydroxide solution.
2. 1M Ammonia solution.
3. 0.5M Acidified Barium Nitrate solution.
4. 1M sulphuric (VI) acid.
5. Acidified potassium Manganate (VII)
6. Source of heat.

NB

1. Solution A 0.02M of H⁺/KMnO₄ is prepared by dissolving 3.16g of KMnO₄ in 400cm³ of 2M H₂SO₄. Add distilled water to make 1 litre of solution.
2. 1M sodium hydroxide is prepared by dissolving 40 g of sodium hydroxide dissolved in about 200cm³ of distilled water in a 1000 ml volumetric flask and top up with distilled water to the mark.
3. Acidified Barium Nitrate solution is prepared by dissolving 26.1g of Barium Nitrate in 400cm³ of 2M nitric acid and top up to 1 litre of solution using distilled water.
4. 2M Sulphuric acid. Prepared by dissolving 110cm³ of concentrated Sulphuric acid in about 600cm³ of distilled water and diluting to one litre of solution.
5. Solution B 0.05M oxalic prepared by dissolving 6.3g of dehydrated oxalic acid in about 400ml of distilled water in a 1 litre volumetric flask and top up to the mark.

MARKING SCHEME

Q1. Table I/procedure I
       Complete table – (1mark)

• 5 values -1mark
• 3-4 values ½ mark
• 1-2 values 0 mark

Decimal place.

• Tied to the time
  Accept time to 2 decimals, 1 decimal or whole number used consistently

Accuracy (1mk)

• Compare the first value with teacher’s value.
  If within range of ±2 units award 1 mark otherwise award 0 mark if outside the range

Trend – (1mark)

• Continuous decrease in time (1mark)
  penalize fully for any inconsistence in the trend

Graph (3mark)

• Scale – ½ mark
  Occupy at least 8 squares on both axes

Labelling axes – ½ mark

• Both axes labelled correctly showing correct variables- ½ mark
  (Units may or may not be given. But if given must be correct. Otherwise penalize fully for wrong units

Plotting 1 mark

• 4-5 correctly plotted points -1mark
• 2-3 correctly plotted points – ½ mark

Shape/curve-1mark
Smooth curve – 1mark

(ii) Correct showing on graph√¹ 1mark. Correct reading from graph – (1 mark)
(iii). Rate of reaction increase with increase in temperature√ 1mark

Procedure II
Table

• Complete Table (C.T- 1 mark
• C.T with 3 titrations 1 mark
• C.T with 2 titrations 1 mark
• C.T with 1 0 mark

Penalties

• Inverted table penalize ½ mark
• Wrong arithmetic ½ mark
• Unrealistic values below 1cm3 and above 50cm3 penalize ½ mark
• NB/ penalize to a maximum of ½ mark

Decimal place (D.P) (1mark)

• Values to 1 d.p or 2 d.p of 25, 50, 75 i.e
• 2^nd d.p should be 0 or 5

Accuracy (A) – 1mark

• If any value is within the range 0.1 of school value award 1 mark
• If any value is within the range of 0.2 of school value award ½ mark

Principle of averaging (P.A) – 1mark

• Average value that are 0.2 of each other (1mark)

Final answer/accuracy (F.A) – 1mark

• Compare the averaged value with school value.
• If within range of 01 1mk, if range of 0.2 ½ mark

(ii). RFM of (NH₄)₂SO₄. FeSO₄. 6H₂O = 392

                 ∴concentration = ^19.6/₃₉₂√1

               = 0.05moles√1 (2marks)

(iii). Moles of C used = (1mark)

                    0.05 x 25 √½ = 0.00125 moles√½
                        1000

(iv). Moles of A used = ¹/₅ x 0.00125½(1mark)
                                  = 0.00025 moles √½

(v) Average tire → 0.00025 moles   (1mark)
                       1000cm³ → 
                        0.00025 x 1000√1 = correct answer √1
                            Average tutre

Q2.
     (i).

Observations	Inferences
Colourless liquid condenses on cooler part of test tube Blue litmus changes to red and red remains red. Yellow solid formed (Any 2 ( ½ x 2)	Hydrated/contains water of crystallisation. Tied to colour liquid condenser SO42- SO32- CO32- present   (Any one for ½ mark each)

 

   (ii)
  

Observations	Inferences
Dissolves ½ forming colourless ½ solution	Soluble salt/substance √1 ½ mark for Absence of Cu2+ Fe2+Fe3+ ions

  (a).

Observations	Inferences
White ppt√1/2 soluble in excess√1/2	Zn2+,Pb2+, Al3+ present√1 (3 ions 1 mk) (2 ions ½ mark 1 ion 0mk Correctly inferred Penalize ½ mark each for any contradictory ion to a maximum of 1 mark

  (b).

Observations	Inferences
No white precipitate No effervescence	Zn2+, Al3+ present√1 Pb2+ absent for ½ mk SO32- CO32- absent The cations must be mentioned in (a) above.

  (c)

Observations	Inferences
White precipitate √½soluble in excess ½ (1mk)	Zn2+ √1 Present (1mk)

  (d).

Observations	Inferences
White precipitate formed√1 (1mk)	SO42- present√1 (1mk)

Q3.
     (a)
           (i)

Observations	Inferences
Solid dissolve√½ to form colourless solution √½	Polar substance √1

          (ii).

Observations	Inferences
Decolourize potassium manganite(VII) /potassium manganite (VIII) change from purple to colourless

         (iii).

Observations	Inferences
Effervescence/bubbles/fizzing (1mk)	R-COOH present (1mk)

     (b).

Observations	Inferences
Burns with yellow/ sooty/luminous flame (1 mark)

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