Chemistry Paper 3 Questions and Answers - Maranda Mock Examinations 2022

Instructions to candidates

1. Answer ALL questions in the spaces provided on the question paper
2.  You are NOT allowed to start working with the apparatus for the first 15 minutes of the 2¼ hours allowed for this paper. This time is to enable you to read the question paper and make sure you have all the apparatus and chemicals that you may need.
3. All working MUST be clearly shown where necessary
4. Mathematical tables and silent non-programmed electronic calculators may be used.

QUESTIONS

1. You are provided with:
   • Solid K – Magnesium ribbon
   • Solution L – 2.0M Hydrochloric acid
   • Solution C – 0.4 M Sodium hydroxide solution
   • Stopwatch

You are required to determine:

• the rate of reaction between magnesium and hydrochloric acid at different concentrations
• Mass of magnesium ribbon that reacted

PROCEDURE I

1. Place the five test tube on the test tube rack and label them 1, 2, 3, 4 and 5. Using a 10 cm3 measuring cylinder, measure out the volumes of 2.0 M hydrochloric acid, Solution L, as shown in table 1 below and pour them into the corresponding test tube. RETAIN the remaining solution L for use in question 2 and 3. Wash the measuring cylinder and use it to measure volumes of water as indicated in the table and pour into the corresponding test tubes.
2. Cut out FIVE pieces each of exactly 1 cm length of magnesium ribbon, Solid K.
3. Transfer all the solution in test tube 1 into a clean 100 cm3 beaker. Place one piece of magnesium ribbon into the beaker and start the stopwatch immediately. Swirl the beaker continuously ensuring that the magnesium is always inside the solution. Record in the table the time taken for the magnesium ribbon to disappear. TRANSFER carefully the contents of the beaker into the 250ml volumetric flask. Add 10 cm3 of distilled water into the beaker, swirl and add it to the volumetric flask. Retain this for Procedure II.
4. Repeat procedure (iii) for each of the solutions in test tube 2, 3, 4 and 5 and complete the table I below.

Table 1

Test tube Number	1	2	3	4	5
Volume of solution L (cm3)	10	9	8	7	6
Volume of water added (cm3)	0	1	2	3	4
Time taken for the ribbon to disappear (sec.)
Rate of reaction (1/time) s-1

(5 marks)
b)

1. Plot a graph of rate of reaction (1/time) (y-axis) against volume of solution L. (3 marks)
2. Using the graph, determine the time that would be taken for a 1 cm length of Magnesium ribbon to disappear if the volume of the acid was 7.5 cm³. (1 mark)

PROCEDURE II
To the contents of 250ml volumetric flask from Procedure I, add distilled water to the mark while shaking. Label this as solution D. Fill the burette with solution C. Pipette 25 cm³ of solution D into a 250 cm³ conical flask. Add three drops of phenolphthalein indicator and titrate with solution C. Record the results in table 2. Repeat the titration and complete table 2.
Table 2

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

(4 marks)

1. Determine the average volume of solution C used. (1 mark)
2. Calculate the number of moles of:
   1. Sodium hydroxide in solution C used. (1 mark)
   2. Hydrochloric acid in 25cm³ of solution D. (1 mark)
   3. Hydrochloric acid in 250 cm³ of solution D. (1 mark)
   4. Hydrochloric acid in 40 cm³ of solution L (1 mark)
   5. Hydrochloric acid that reacted with Magnesium. (1 mark)
3. Determine the mass of Magnesium that reacted. (Mg =24.0) (1 mark)

2. You are provided with solid E. Carry out the following tests and write your observations and inferences in the spaces provided.

1. Place all of solid E in a boiling tube. Add about 10 cm³ of distilled water and shake thoroughly. Filter the mixture into another boiling tube. Retain the filtrate for use in test 2(b) below. Dry the residue using pieces of filter papers.
   1. Place the residue in a dry test-tube. Add 4 cm³ of 2M hydrochloric acid, solution L. Retain the mixture for test (iii) below.

Observations	Inferences
( ½  mark)	(1mark)

ii).  To 2 cm³ of the solution obtained in (i) above, add aqueous ammonia dropwise until in exess.

Observations	Inferences
(1 mark)	(1mark)

b). Use about 2 cm³ of the filtrate obtained in (a) above for tests (i) to (iii) below.
i) Add aqueous ammonia dropwise until in excess.

Observations	Inferences
(1 mark)	(1mark)

ii) Add about 2 cm³ of 2M hydrochloric acid, solution L.

Observations	Inferences
(1 mark)	(1mark)

iii) Add aqueous sodium hydroxide dropwise until in excess.

Observations	Inferences
(½ mark)	(1mark)

iv). Add three drops of barium nitrate solution.

Observation	Inference
(1mark)	(1mark)

3. You are provided with solid F. Carry out the following tests. Write your observations and inferences in the spaces provided

a. Place all of solid F in a boiling tube. Add about 20 cm³ of distilled water and shake until all the solid dissolves. Label the solution as solution F.

Add about half of the solid sodium hydrogen carbonate provided to 2 cm³ of solution F.

Observations	Inferences
( ½  mark)	( ½  mark)

(i) Add about 10 cm³ of dilute hydrochloric acid, solution L, to the rest of solution F in the boiling tube. Filter the mixture. Wash the residue with about 2 cm³ of distilled water. Dry the residue between filter papers. Place about one third of the dry residue on a metallic spatula and burn it in a Bunsen burner flame.

Observations	Inferences
(l mark)	(l mark)

(ii) Place all the remaining residue into a boiling tube. Add about 10 cm³ of distilled water and shake thoroughly. Retain the mixture for tests in (c).

Observations	Inferences
(l mark)	(l mark)

1. Divide the mixture into two portions:
   • To the first portion, add the rest of the solid sodium hydrogen carbonate.

Observations	Inferences
(½ mark)	( ½  mark)

To the second portion, add two drops of bromine water.

Observations	Inferences
(1  mark)	(1 mark)

CONFIDENTIAL

INSTRUCTIONS TO SCHOOLS

In addition to the fittings and apparatus found in a chemistry laboratory, each candidate will require the following:

A: Each candidate

1. About 80cm³ of solution L
2. About 100cm³ of solution C
3. About 80cm³ of solution
4. One burette 0 – 50 ml
5. One pipette 25.0ml and a pipette filler
6. One Filter funnel
7. 100ml beaker
8. Solid K
9. Two clean dry 250 ml conical flasks
10. Six (6) clean and dry test tubes on a test tube rack
11. One boiling tube
12. 2g of solid sodium hydrogen carbonate supplied in a stoppered container
13. About 500cm³ of distilled water supplied in a wash bottle
14. One 250ml volumetric flask
15. 4 filter papers (125mm Whatman no. 1)
16. One 10ml measuring cylinder
17. Seven (7) labels
18. One metallic spatula
19. One test tube holder
20. One stopwatch
21. A white tile
22. About 1.0g of solid E supplied in a stoppered container
23. About 0.5g of solid F supplied in a stoppered container

B: Access to:

1. Phenolphthalein indicator supplied with a dropper
2. Bunsen burner
3. 0M aqueous ammonia supplied with a dropper
4. 0M sodium hydroxide solution supplied with a dropper
5. Bromine water supplied with a dropper
6. 5M Barium (II) nitrate solution supplied with a dropper

C: Preparation of solutions and solids

1. Solution L is prepared by accurately adding 172cm³of concentrated hydrochloric acid (density 1.18gcm³) to about 500cm³ of distilled water and diluting with distilled water to make one litre solution.
2. Solution C is prepared by dissolving 8.0g of sodium hydroxide in 700cm³ of distilled water and diluting it to one litre.
3. Solid E is a mixture of zinc carbonate and magnesium sulphate in the ratio 1:1
4. Solid F is sodium benzoate
5. Solid K is 6 cm long Magnesium ribbon

Instructions to candidates

1. Answer ALL questions in the spaces provided on the question paper
2.  You are NOT allowed to start working with the apparatus for the first 15 minutes of the 2¼ hours allowed for this paper. This time is to enable you to read the question paper and make sure you have all the apparatus and chemicals that you may need.
3. All working MUST be clearly shown where necessary
4. Mathematical tables and silent non-programmed electronic calculators may be used.

MARKING SCHEME

1. You are provided with:
   • Solid K – Magnesium ribbon
   • Solution L – 2.0M Hydrochloric acid
   • Solution C – 0.4 M Sodium hydroxide solution
   • Stopwatch

You are required to determine:

• the rate of reaction between magnesium and hydrochloric acid at different concentrations
• Mass of magnesium ribbon that reacted

PROCEDURE I

1. Place the five test tube on the test tube rack and label them 1, 2, 3, 4 and 5. Using a 10 cm3 measuring cylinder, measure out the volumes of 2.0 M hydrochloric acid, Solution L, as shown in table 1 below and pour them into the corresponding test tube. RETAIN the remaining solution L for use in question 2 and 3. Wash the measuring cylinder and use it to measure volumes of water as indicated in the table and pour into the corresponding test tubes.
2. Cut out FIVE pieces each of exactly 1 cm length of magnesium ribbon, Solid K.
3. Transfer all the solution in test tube 1 into a clean 100 cm3 beaker. Place one piece of magnesium ribbon into the beaker and start the stopwatch immediately. Swirl the beaker continuously ensuring that the magnesium is always inside the solution. Record in the table the time taken for the magnesium ribbon to disappear. TRANSFER carefully the contents of the beaker into the 250ml volumetric flask. Add 10 cm3 of distilled water into the beaker, swirl and add it to the volumetric flask. Retain this for Procedure II.
4. Repeat procedure (iii) for each of the solutions in test tube 2, 3, 4 and 5 and complete the table I below.

Table 1

Test tube Number	1	2	3	4	5
Volume of solution L (cm3)	10	9	8	7	6
Volume of water added (cm3)	0	1	2	3	4
Time taken for the ribbon to disappear (sec.)
Rate of reaction (1/time) s-1

(5 marks)
b)

1. Plot a graph of rate of reaction (1/time) (y-axis) against volume of solution L. (3 marks)
2. Using the graph, determine the time that would be taken for a 1 cm length of Magnesium ribbon to disappear if the volume of the acid was 7.5 cm³. (1 mark)

PROCEDURE II
To the contents of 250ml volumetric flask from Procedure I, add distilled water to the mark while shaking. Label this as solution D. Fill the burette with solution C. Pipette 25 cm³ of solution D into a 250 cm³ conical flask. Add three drops of phenolphthalein indicator and titrate with solution C. Record the results in table 2. Repeat the titration and complete table 2.
Table 2

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

(4 marks)

1. Determine the average volume of solution C used. (1 mark)
   = titre 1 + titre 2 + titre 3
                    3
   = average titre
2. Calculate the number of moles of:
   1. Sodium hydroxide in solution C used. (1 mark)
      = 0.4 x average titre
              1000
      correct answer
   2. Hydrochloric acid in 25cm³ of solution D. (1 mark)
      mole ratio Hcl: NaOH is 1:1
      = answer in b(i) above
   3. Hydrochloric acid in 250 cm³ of solution D. (1 mark)
      Answer b(ii) x 250
                   25
      = correct answer
   4. Hydrochloric acid in 40 cm³ of solution L (1 mark)
      = 40 x 2
         1000
      = 0.08
   5. Hydrochloric acid that reacted with Magnesium. (1 mark)
      = answer (iv) - answer (iii)
      = correct answer
3. Determine the mass of Magnesium that reacted. (Mg =24.0) (1 mark)
   Mg(s) + 2Hcl(aq) -> MgCl2 (aq) + H2 (g)
   =answer (v) x 24
          2
   = correct answer
   
   OR
   
   ratio Mg:HCl is 1:2
   = Answer (v) x 24
           2
   = correct answer

2. You are provided with solid E. Carry out the following tests and write your observations and inferences in the spaces provided.

1. Place all of solid E in a boiling tube. Add about 10 cm³ of distilled water and shake thoroughly. Filter the mixture into another boiling tube. Retain the filtrate for use in test 2(b) below. Dry the residue using pieces of filter papers.
   1. Place the residue in a dry test-tube. Add 4 cm³ of 2M hydrochloric acid, solution L. Retain the mixture for test (iii) below.

Observations	Inferences
effervescence/bubbles of a colourless gas rej:  - hissing - fizzing ( ½  mark)	CO2-3 Penalise fully for any contradicting ion (1mark)

ii).  To 2 cm³ of the solution obtained in (i) above, add aqueous ammonia dropwise until in exess.

Observations	Inferences
white precipitate soluble in excess  (or dissolves in excess to form a colourless solution) rej; a soluble white precipitate (1 mark)	Zn2+ (1mark)

b). Use about 2 cm³ of the filtrate obtained in (a) above for tests (i) to (iii) below.
i) Add aqueous ammonia dropwise until in excess.

Observations	Inferences
white precipitate insoluble in excess rej: insoluble white ppt (1 mark)	Al3+, Pb2+, Mg2+ present conditions - 3 correct ions - 1 mk - 2 correct ions - 1/2 mk - only 1 correct ion - 0 mk NB: penalise 1/2 mk for each contradictory ion to max of 1 mk (1mark)

ii) Add about 2 cm³ of 2M hydrochloric acid, solution L.

Observations	Inferences
no effervescence no white precipitate  (1 mark)	CO2-3, SO2-3 absent award 1/2 mk for both ions tied to no effervescence Al3+, Mg2+ present must be correctly inferred in b(i) above otherwise penalise fully  Pb2+ absent  (1mark)

iii) Add aqueous sodium hydroxide dropwise until in excess.

Observations	Inferences
white precipitate insoluble in excess  rej; insoluble white ppt (½ mark)	Mg2+ present (1mark)

iv). Add three drops of barium nitrate solution.

Observation	Inference
white precipitate  penalise fully for white ppt soluble  (1mark)	SO2-4 present penalise fully for any contradictory ion mentioned (1mark)

3. You are provided with solid F. Carry out the following tests. Write your observations and inferences in the spaces provided

a. Place all of solid F in a boiling tube. Add about 20 cm³ of distilled water and shake until all the solid dissolves. Label the solution as solution F.

Add about half of the solid sodium hydrogen carbonate provided to 2 cm³ of solution F.

Observations	Inferences
no efeervescence / no bubbles ( ½  mark)	H+, H3O+, R-COOH absent ( ½  mark)

(i) Add about 10 cm³ of dilute hydrochloric acid, solution L, to the rest of solution F in the boiling tube. Filter the mixture. Wash the residue with about 2 cm³ of distilled water. Dry the residue between filter papers. Place about one third of the dry residue on a metallic spatula and burn it in a Bunsen burner flame.

Observations	Inferences
Burns with a sooty yellow flame (l mark)	(aromatic cpds long-chain alkanes) (l mark)

(ii) Place all the remaining residue into a boiling tube. Add about 10 cm³ of distilled water and shake thoroughly. Retain the mixture for tests in (c).

Observations	Inferences
white suspension/ white solid / white solid remains undissolved rej; white ppt/ undissolves residue alone (l mark)	compound slightly soluble partially soluble rej; solid F is insoluble col we are using its portion to conduct test (l mark)

1. Divide the mixture into two portions:
   • To the first portion, add the rest of the solid sodium hydrogen carbonate.

Observations	Inferences
effervescence / bubbles of a colourless gas  (½ mark)	H+, H3O+, R-COOH rej; mention of F being an acid but accept for 1/2 mk F is acidic ( ½  mark)

To the second portion, add two drops of bromine water.

Observations	Inferences
Bromine water is not decolourised yellow bromide water remains yellow/ yellow colour of bromide water persists (1  mark)	absent (1 mark)

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