Chemistry Paper 3 Questions and Answers - Kijiset Revision Mock Exams 2022

Questions

Instructions to candidates

• Answer all the questions in the spaces provided in the question paper.
• You are not allowed working with the apparatus for the first 15 minutes of the 21/4 hours allowed for this paper. This time is to enable you the question paper and ensure you have all the chemicals and apparatus that you may need.
• All workings must be clearly shown where necessary.
• Mathematical tables and silent electronic calculators may be used.

Question 1.
You are provided with the following:

• Solution A containing 95g of a mixture of sodium carbonate and sodium chloride per litre of solution.
• 1M HCl solution B

You are required to determine the percentage of sodium chloride in the mixture

Procedure:
Pipette 25cm3 of A and place it in a conical flask. Titrate with B from the burette using 3 drops of methyl orange indicator until a permanent pink colour appears. Repeat the experiment and complete the table below.

Table I

(4mks)

1. Calculate the average volume of B used. (1mk)
2. Determine the number of moles of B used (1mk)
3. Write the ionic equation for the substance that react. (1mk)
4. Calculate:
   1. the number of moles of the base used (1mk)
   2. the concentration of sodium carbonate (2mks)
   3. the mass of sodium carbonate in 1 litre of the solution. (Na=23, C=12, O=16) (2mks)
   4. the percentage of sodium chloride in the mixture (1mk)

Question 2.
You are provided with:
-1M HCl solution B
-1M NaOH solution C

You are expected to determine the Molar heat of Neutralization hydrochloric acid

Procedure:
Measure 23cm³ of solution B and put it in a 100ml beaker. Measure its temperature and record in the table below under first column. By use of measuring cylinder, measure 5cm³ of solution C and add to solution B in the beaker. Stir with the thermometer and record the final steady temperature. Continue adding 5cm³ at a time and record the temperature till 35cm³ has been added.

1. Complete the table below (4mks)
   

   Volume of C added(cm3)	0	5	10	15	20	25	30	35
   Temperature (°C)

2. Plot a graph of temperature (vertical axis) against volume of NaOH added. (3mks)
3. From your graph, determine:
   1. Volume of 1M NaOH needed to neutralize 23cm3 of 1M HCl (1mk)
   2. Rise in temperature ∆T (1mk)
4. Calculate the amount of heat evolved in the above reaction. (Take specific heat capacity of solution to be 4.2J/g/K, density of solution, 1g/cm3) (2mks)
5. Calculate :
   1. the number of moles of HCl used (1mk)
   2. hence determine the Molar heat of neutralization of hydrochloric acid (2mks)

Question 3.
You are provided with mixture P. You are required to perform tests on the mixture in order to determine its composition. Record your observations and inferences in the spaces provided.

1. Place a spatula of solid P on a white tile and observe its appearance
   

   Observation	Inferences

2. Place the remaining portion of solid P in a boiling tube and add 10cm³ of distilled water. Shake vigorously, filter and retain both the residue and filtrate.
   

   Observation	Inferences

   
   
   1. Divide the filtrate into 3 portions. To the first portion, add sodium hydroxide drop-wise until excess.
      

      Observation	Inferences

   2. Dip a glass rod in the second portion and place it at the hottest part of the non-luminous flame.
      

      Observation	Inferences

   3. To the third portion, add 3 drops of dilute HNO³(aq), followed by 3 drops of BaCl_2(aq).
      

      Observation	Inferences

3. Scrap the residue from the filter paper and place a half of it in a clean dry test-tube. Add about 3cm³ of 2M HNO³(aq). Test foe any gas produced by use of calcium hydroxide solution on a glass rod. Preserve the solution for use in procedure (d) below.
   

   Observation	Inferences

4. Add about 3cm³ of distilled water to the solution obtained in (c) above and shake to mix. Divide the solution into 3 portions.
   1. To the first portion, add sodium hydroxide drop-wise until excess.
      

      Observation	Inferences

   2. To the second portion, add ammonia solution drop-wise until in excess.
      

      Observation	Inferences

   3. To the third portion, add 2 drops of potassium iodide solution.
      

      Observation	Inferences

Confidential

REQUIREMENTS
In addition to the equipment, apparatus and chemicals found in the Chemistry laboratory, each candidate will require the following:

1. 100cm3 of solution B
2. 80cm3 of solution A
3. 50cm3of solution C
4. 25ml pipette
5. 50ml Burette
6. 2 conical flasks
7. Filter funnel
8. Filter paper
9. 10ml Measuring cylinder
10. 50ml Measuring cylinder
11. Thermometer (-10 to 1100C)
12. 100ml plastic beaker
13. 6 test-tubes on a test-tube rack
14. 1 Boiling tube
15. White tile
16. Stand and clamp
17. Solid P in a stoppered container
18. A glass rod
19. Metallic spatula
20. Distilled water in a wash bottle
21. Calcium hydroxide in a stoppered container

Access to:

1. Methyl orange indicator with a dropper
2. 2M sodium hydroxide with a dropper
3. 2M nitric (V) acid with a dropper
4. 2M ammonia solution with a dropper
5. 0.5M barium chloride with a dropper
6. 0.05M potassium iodide with a dropper
7. 2M hydrochloric acid with a dropper
8. Source of heat

Preparation of solutions:

1. Solid P is the mixture of Lead (II) carbonate and Sodium sulphate in the ratio of 1:1.
2. Solution A is prepared by mixing 53g of sodium carbonate and 42g of sodium chloride solid and dissolving to make one litre of solution.
3. Solution B is prepared by dissolving 86cm3 of concentrated hydrochloric acid in distilled water and dilute to one litre.
4. Solution C is prepared by dissolving 40g of sodium hydroxide pellets in distilled water and top up to one littre.

Marking scheme

QUESTION 1

Table 1

A ward a total of 5 mks as follows

1. Complete table 1 mk
   
   1. Complete table with 3 titrations 1mk
   2. Incomplete table with 2 titrations ½
   3. Incomplete table with only 1 titration done 0 mk
      
      Penalties
      • Wrong arithmetic/ subtraction
      • Inverted table
      • Burette reading beyond 50cm3
      • Unrealistic titre value ie 1.0cm3
        
        NOTE: Penalize ½mk for each for a maximum penalty of ½
2. Use of decimals (tied to the 1st and 2nd row only) 1mk
   1. Accept either 1 or 2 decimals used CONSISTENTLY , otherwise penalize fully.
   2. If 2 decimal places are used the 2nd decimal must be 0 or 5 otherwise penalize fully.
3. Accuracy 1mk
   1. Compare candidate titre value with the school value (SV)
   2. If at  least one value is within ±0.1 award 1mk
   3. If within ±0.2 of the SV award ½
   4. If no value is within ±0.2 of the SV award 0mk
4. Principle of averaging
   Value average must be shown and must be within 0.2 of each other ½mk, followed by ½mk for the correct answer.
   
   NOTE
   1. If 3 values are possible but averaged, award 0mk
   2. If 3 titration are done, are inconsistent and averaged, award 0mk
   3. If only 2 titrations are done, are consistent and averaged, award 0mk
5. Final answer (tied to correct average titre)  1mk
   Compare the candidate CORRECT AVERAGE TITRE with the SV
   1. If it is within 0.1 of S.V, award 1mk
   2. If it is within 0.2 of S.V, award ½mk
   3. If it is beyond 0.2 of S.V, award 0mk

Calculations

1. Table 2
   • Complete table 1mk
   • Accuracy 1mk
   • Decimal place 1mk
     Accept 1d.p or whole number for temperature readings
     Award 0mk if the second d.p is not 0 or 5 
   • Reject 2d.p
   • trend 1mk
     Temperature readings to increase then decrease.
2. Graph
   1. Labelled axes ½mk
      Award half a mark if both axes are correctly labelled (temeparture (°C) vertical axis) against colume (cm3) on horizontal axis.
   2. Scale ½mk
      • Area covered by the actual plots must be at least half.
      • Scale interval must be consistent
      • Scale chose must accomodate all plot
   3. Plot
      • If 7 to 8 are correctly plotted 1mk
      • If 4 to 6 plots are correctly plotted half a mark
      • Otherwise a ward 0mk
   4. Shape 1mk
      • Accept straight lines of best fit, one for increase in temperature and another for decrease joined with dotted lines at a vertex 1mk
3.  
   • From the graph
   • Shown in graph
   • Correct reading
     ΔT - 
     
     • Shown in graph
     • correct answer from graph
4. ΔH = MCΔT = (23 + C(i) x 4.2 x c(ii))
   correct ans
5. Moles =   1 x 23  
                  1000
   = 0.023 moles

Question 3