Chemistry Paper 3 Questions and Answers - Momaliche Pre Mock Exams 2023

INSTRUCTIONS TO CANDIDATES.

• Answer ALL the questions in the spaces provided.
• You are not allowed to start working with the apparatus for the first 15 minutes of the 2¼ hours allowed time for the paper.
• Use the 15 minutes to read through the question paper and make sure that you have all the chemicals and apparatus that you may require.
• Mathematical tables and electronic calculators may be used.
• All working MUST be clearly shown where necessary.

Question 1

You are provided with:-

• 2.0 g solid A.
• 2.0 M hydrochloric acid  solution B.
• 0.1M Sodium hydroxide solution
  You are required to determine the;
  1. Enthalpy change (∆H )for the reaction between solid A and one mole of hydrochloric acid.

PROCEDURE I

Using a burette,place 20.0cm³ of 2.0M hydrochloric acid,solution B in a 100cm³ plastic beaker.Measure the temperature of the solution after every half-minute and record the values in table 1.At exactly 2 ½ minutes, add all of solid A to the acid and stir the mixture gently with the thermometer. Measure the temperature of the mixture after every half-minute and record the values in table 1.Retain the mixture for use in procedure II.

Table 1

(3mks)

1. Plot a graph of temperature against time.                                                             (3mks)
   Using the graph, determine the change in temperature (∆T)                                           (1mk)
2. Calculate heat change for the reaction.(Assume specific heat capacity of the mixture is 4.2J/g/K, Density of solution=1.0g/cm³))                                                                             (2mks)

Procedure II

Rinse the burette thoroughly and fill with sodium hydroxide solution. Transfer all the contents of 100cm³ plastic beaker used in procedure I into a 250cm³ volumetric flask. Add distilled water to make up to the mark. Label this solution C.

Using a  pipette and pipette filler, place 25cm³ of solution C into a clean conical flask and add 2 drops of phenolphthalein indicator and titrate against sodium hydroxide solution. Record your results in table 2 below. Repeat the titration two more times to complete the table 2 below.

TABLE I

(4mks)

1. Determine the average volume of sodium hydroxide solution A used.    (1 mk)
2. Calculate number of moles of;
   1. sodium hydroxide used  (1 mk)
   2. hydrochloric acid in 25cm³ of solution C  . (1 mk)
   3. hydrochloric acid in 250cm³ of solution C  .    (1 mk)
   4. hydrochloric acid in 20cm³ of solution B.     (1 mk)
   5. hydrochloric acid that reacted with solid A.   (1 mk)
3. Calculate the enthalpy of reaction between solid A and one mole of hydrochloric acid solution B.     (1mk)

Question 2

You are provided with solid E,F and G. Carry out the tests below  and write the observations and inferences  in the spaces provided. 

1. Place all solid E in a boiling tube and add about 15cm³ of distilled water. Shake the boiling tube until all the solid dissolves. Label this solution E. Divide the solution E into 4 portions.
   

   Observations	Inferences
   (1mk)	(1mk)

   1. To the first portion of solution E in a test tube, add 4 drops of 2M  sulphuric (VI) acid.
      

      Observations	Inferences
      (1mk)	(1mk)

   2. To the second portion of solution E in a test tube,add sodium hydroxide drop wise until in excess.
      

      Observations	Inferences
      (1mk)	(1mk)

2. Place one half of solid F in a test tube .Add 2cm³ of distilled water and shake well. Add  3 drops of this solution to the third portion of solution E.
   

   Observations	Inferences
   (1mk)	(1mk)

3. To the fourth portion of solution E in a test tube ,add 2 drops of aqueous potassium iodide.
   

   Observations	Inferences
   (1mk)	(1mk)

   1. Name the  cation  present in solid E………………………………..                                        (1mk)

Question 3

You are provided with solid  G. Carry out the tests below  and write the observations and inferences  in the spaces provided. 

1. Using a metallic spatula, place a third of solid G and ignite on a non-luminous flame.
   

   Observations	Inferences
   (1mk)	(1mk)

2. Place the remaining solid G in a boiling tube. Add 10cm³ of distilled water and shake well. Label this solution G. Use the solution G for the tests below.
   1. To the first portion of solution G in a test tube, determine its pH value.
      

      Observations	Inferences
      (1mk)	(1mk)

   2. To the second portion of solution G in a test tube,addd 3 drops of acidified potassium manganite (VII).
      

      Observations	Inferences
      (1mk)	(1mk)

   3. To the third portion of solution G in a test tube, add 2 drops of bromine water.
      

      Observations	Inferences
      (1mk)	(1mk)

   4. To the fourth portion of solution G in a test tube,add the remaining solid F.
      

      Observations	Inferences
      (1mk)	(1mk)

CONFIDENTIAL

1. 2.0 g solid A weighed accurately and supplied in a stoppered container.
2. About 60cm³ solution B
3. About 130cm³ Sodium hydroxide solution  
4. One thermometer -10⁰C -  110⁰C
5. One Stop watch
6. One 100ml plastic beaker
7. One burette 0-50ml
8. One pipette
9. One volumetric flask
10. About 500ml distilled water
11. 3 labels
12. 2 Conical flasks
13. One 10ml measurimg cylinder
14. One 100ml measurimg cylinder
15. One boiling tube
16. 0.5g Solid E
17. 6-clean dry test tubes
18. 0.2g Solid F
19. 0.5g Solid G
20. pH Chart  
21. Metallic spatula
22. Six droppers

ACCESS TO 

• 2M NaOH
• 2M Sulphuric (VI) acid
• 0.5M Potassium iodide
• Bromine water
• Barium chloride soln. (BaCl₂)
• Universal indicator soln
• Acidified KmnO₄.
• Phenolphthalein indicator
• Source of heating

NOTES

1. Solid A —Borax salt.
2. Solid E-Lead Nitrate 
3. Solid F-Sodium Carbonate
4. Solid G-.Maleic acid

PREPARETIONS

1. Solution B is prepared by adding 172cm³ (1.18g/cm³)of concentrated hydrochloric acid to about 500ml distilled water and diluting to  1 Litre solution.
2. Sodium hydroxide solution is prepared by dissolving 4gms of the soild in about 500ml of water then diluting to 1 Litre (0.1 M).
3. Bromine water is prepared 1ml of liquid water and dissolving it 100ml of distilled water in a fume chamber.(Freshly Prepared).
4. Acdified KMnO₄ is prepared by dissolving 3.16g of solid potassium manganate(VII) in about 200ml of 2M Sulphuric (VI) acid and top up to 1 Litre of distilled water.

MARKING SCHEME

Question 1

PROCEDURE 1

Table 1 

CT = 1
TR = 1
D = 1

1.  
   
   Change in temperature 
   20 − 10 = 5.0 (after extrapolation)
2. ΔH = 0.42kJ

PROCEDURE II

TABLE I

CT = 1
D = 1
AC = 1
PA = 1
FA = 1

1. 15.0cm³
2.  
   1. = 0.0015 moles
   2. Mole ratio 1:1 hence 0.0015 moles HCl solution C used
   3. = 0.015 moles
   4. = 0.04 moles
   5. 0.04 − 0.015 = 0.025 moles
3. = + 16.8 kJ/mole

Question 2

1.  
   

   Observations	Inferences
   Solid E dissolves to form a colourless solution (1mk)	- A soluble salt present - Cu2+,Fe2+,Fe3+ absent (1mk)

   1.   
      

      Observations	Inferences
      A white precipitate formed (1mk)	Ca2+ ,Pb2+ ,Ba2+ present (1mk)

   2.  
      

      Observations	Inferences
      A white precipitate dissolves in excess (1mk)	Pb2+ present (1mk)

2.  
   

   Observations	Inferences
   A white precipitate formed (1mk)	Cl- ,CO32- ,SO42- ,SO32- present (1mk)

3.  
   

   Observations	Inferences
   A yellow precipitate (1mk)	Pb2+ present (1mk)

   • Solid E = Lead (II) ions (1mk)

Question 3

1.   
   

   Observations	Inferences
   Solid G melts and burns with a yellow sooty flame (1mk)	(1mk)

2.  
   1.   
      

      Observations	Inferences
      pH value is 1,2  (1mk)	Solution is strongly acidic (1mk)

   2.  
      

      Observations	Inferences
      Purple colour of potassium manganite(VII) solution changes to colourless (1mk)	R -OH Present(1mk)

   3.  
      

      Observations	Inferences
      Yellow colour of bromine water changes to colourless     (1mk)	(1mk)

   4.  
      

      Observations	Inferences
      Effervescence occurs. (1mk)	CO32-  Present (Tied to part 2(b) above).   (1mk)