Chemistry Paper 3 Questions and Answers with Confidential - Lanjet Joint Mock Exams 2023

INSTRUCTIONS TO CANDIDATES

• 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 note the chemicals you require
• Mathematical tables and electronic calculators may be used.
• All working MUST be clearly shown where necessary.

QUESTION 1

You are provided with the following:

• Solution A potassium iodide solution
• “ B sodium thiosulphate
• “ C acidic solution
• “ D Starch solution
• “ E Hydrogen peroxide
• Distilled water

You are required to determine the rate of reaction between solution A and solution B

Procedure

Step 1

Place 10cm³ of solution A using 10ml measuring cylinder into a 100ml beaker.
Add 2cm³ of solution B followed by 2cm³ of solution C. In same beaker, Add 5 drops of solution D and finally 12cm³ of distilled water and shake the mixture.

Step 2

Using a burette, place 6cm³ of solution E into a test tube. Pour the measured 6cm³ of solution E into beaker in step 1 above and immediately start the stop watch. Swirl the mixture and place it on a white paper or tile. Observe the mixture and note the time taken for blue colour to appear.

Record the time taken in table 2

Measure the temperature of the mixture and record table 2.

Step 3

Repeat the step 1 and 2 using the volumes of solution given in table for experiments 2, 3, 4, 5 and 6, record in table below.

Table 1

1. Calculate the rate of reaction 1/time 5^-1 for each of experiments and fill table 2 below.
   Table 2
   

   experiment number	Volumes of solution   A (cm3)	Temp of solution  (°C)	Time  (sec)	Rate 1/t sec -1
   1	2
   2	4
   3	6
   4	8
   5	10
   6	12

                                                                                                                                         (8 marks)
2. Plot the graph of rate of reaction 1/time against volume of solution A. (3 marks)
                                
3. If the experiment was repeated using 5cm³ of potassium iodide solution A, determine;
   1. Volume of distilled water that would be used. (1 mark)
   2. Time taken for blue colour to appear. (2 marks)
4. Explain how rate of reaction is affected by the volume of potassium iodide. (2 marks)
5. Explain why it is necessary to record the temperature each experiment. (1 mark)

QUESTION 2

You are provided with solid F. Carry out the following tests and record your observations and inferences in the space provided.

1. Place all solid F into a boiling tube. Add about 10cm3 of dilute nitric (V) acid, warm the mixture and then allow it to stand until all the solid dissolves. Add about 10cm3 of distilled water to the solution and shake. Retain the solution for tests (b) and (c)
   

   observations	Inferences
   (2 marks)	(1 mark)

2. Use 2cm³ portion of solution obtained in 2(a) for each of the following tests.
   1. To first portion, add 3 drops of Barium Nitrate.
      

      observations	Inferences
      (1 mark)	(1 mark)

   2. To the second portion, add 3 drops of lead (ii) Nitrate solution.
      

      observations	Inferences
      (1 mark)	(1 mark)

   3. To the third portion, add drops of 2MNaOH until in excess.
      

      observations	Inferences
      (1 mark)	(1 mark)

   4. To the fourth portion, add few then excess drops of 2MNH₄OH provided in the access point.
      

      observations	Inferences
      (1 mark)	(1 mark)

3. To the last portion in the boiling tube add all solid G provided. Shake the mixture for about 2 minutes. Filter the mixture into a boiling tube. Retain the filtrate for test below.
   

   observations	Inferences
   (1 mark)	(1 mark)

   
   
   1. To about 2cm³ of filtrate add few then excess drops of 2MNaOH.
      

      observations	Inferences
      (1 mark)	(1 mark)

   2. To about 2cm³ portion of filtrate add 3 drops of hydrogen peroxide solution then excess drops of 2MNaOH.
      

      observations	Inferences
      (1 mark)	(1 mark)

Question 3

You are provided with solid H carry out the following tests and record the observations and inferences in the space provided.

1. Place all solid in a boiling tube then add about 10cm3 of distilled water use the mixture for tests (i) and (ii) below
   

   observations	Inferences
   (1 mark)	(1 mark)

   
   
   1. Using about 2cm³ of the mixture in a test tube, determine the pH using universal indicator and pH chart.
      

      pH	Inferences
      (1 mark)	(1 mark)

   2. To about 2cm³ of the mixture in a test tube, add 3 drops of potassium manganate VII provided in the access.
      

      observations	Inferences
      (1 mark)	(1 mark)

                                                                                   CONFIDENTAL

In addition to fillings found in each candidate must have the following

1. 60cm³ of solution A
2. 20cm³ of solution B
3. 20cm³ of solution C
4. 20cm³ of solution D
5. 60cm³ of solution E
6. Two 10ml measuring cylinder
7. 100ml beaker
8. 500ml distilled water in a wash bottle.
9. Burette
10. Thermometer
11. Stop watch
12. Six test tubes in rack
13. One boiling tube
14. Filter paper
15. Unsed indicator paper and access to pH chart
16. 0.5g of solid F
17. 0.5g of solid G
18. 0.5g of solid H
19. 20cm³ of dilute nitric (v) acid. (21MHMO₃)

Access

• 2MNaOH supplied with a dropper
• 2MNH₄OH supplied with a dropper
• Source of heat supplied with a dropper
• 0.1M Pb (NO₃)₂ supplied with a dropper
• 0.1M Ba (Na₃)₂ supplied with a dropper
• 10 volume H₂O₂ supplied with a dropper
• Acidified potassium manganate VII

Preparation of solutions

• Solution A prepared by dissolving 50g of KI and tapping it up to 1 litre.
• Solution B is prepared by dissolving 5g of sodium thiosulphate in a given amount of water and diluting to 1 litre.
• Solution C prepared by dissolving 30cm³ of ethanoic acid in 1 litre volumetric flask then add 68g of sodium ethanoate followed by 700cm³ of distilled under shake the mixture then top it up to 1 litre.
• Solution D is prepared by placing 10 grammes of starch, make a paste then add to boiling water to make 1 litre of solution.
• Solution E is prepared by placing 60cm³ of 20 volumes hydrogen peroxide in 1 litre volumetric flask then adding distilled water to the mask.
• Solid F is about 0.5g CuO
• Solid G is about 0.5g Fe powder
• Solid H is about 0.5g malleic acid

                                                                                       MARKING SCHEME

QUESTION 1

You are provided with the following:

• Solution A potassium iodide solution
• “ B sodium thiosulphate
• “ C acidic solution
• “ D Starch solution
• “ E Hydrogen peroxide
• Distilled water

You are required to determine the rate of reaction between solution A and solution B

Procedure

Step 1

Place 10cm³ of solution A using 10ml measuring cylinder into a 100ml beaker.
Add 2cm³ of solution B followed by 2cm³ of solution C. In same beaker, Add 5 drops of solution D and finally 12cm³ of distilled water and shake the mixture.

Step 2

Using a burette, place 6cm³ of solution E into a test tube. Pour the measured 6cm³ of solution E into beaker in step 1 above and immediately start the stop watch. Swirl the mixture and place it on a white paper or tile. Observe the mixture and note the time taken for blue colour to appear.

Record the time taken in table 2

Measure the temperature of the mixture and record table 2.

Step 3

Repeat the step 1 and 2 using the volumes of solution given in table for experiments 2, 3, 4, 5 and 6, record in table below.

Table 1

1. Calculate the rate of reaction 1/time 5^-1 for each of experiments and fill table 2 below.
   Table 2
   
                                                                                                                                                                      (8 marks)
2. Plot the graph of rate of reaction 1/time against volume of solution A. (3 marks)
                                
   1. COMPLETE TABLE ................ 5 marks
      Marks distribution for the table, the marks were distributed using the conditions shown in Table below.
      • Complete table with 18 entries (6 temeprature, 6 time and 6 correct rates......5 marks
      • Incomplete table with 6 temperature, 6 time and 4 or 5 correct rates...........4½marks
      • Incomplete table with 6 temperature, 6 time and 3 correct rates .......4 marks
      • Incomplete table with 6 temperature, 6 time and 4 or 5 correct rates......3½ marks
      • Incomplete table with 4 or 5 temperature, 4 or 5 time and 4 or 5 correct rates..........3 marks
      • Incomplete table with 4 or 5 temperature, 4 or 5 time and less than 3 correct rates......2½ marks
      • Incomplete table with 4 or 5 temperature, 4 or 5 time and 3 correct rates..........2½ marks
      • Incomplete table with 3 temperature, 3 time and 3 correct rates.......2½ marks
      • Incomplete table with 3 temperature, 3 time and less than3 correct rates.......2 marks
      • Incomplete table with 2 temperature, 2 swith or without corract rates .....1 mark
      • Incomplete table with 1 temperature, 1 time and with or without correct rates ......½ mark
      • Incomplete table with only one entry award.......0 mark
      • Incomplete table with only time column mark out of 2½marks and penalize ½ mark for each space not fillled on the time column
        Penalties
      • Penalize ½ mark once for unrealistic temperature values less than10°C and more than 40°c
      • Penalize ½ mark once for unrealistic time values less than 5 seconds and more than 420 seconds
      • Penalize ½ mark once for time in minutes
      • If no temperature is given, penalize 1 mark once
      • Accept given to at least 3 decimal places, penalize ½ mark once of a candidate gives in less divides the 3dp places unless it works out exactly to a whole number
      • Penalize ½ mark once for wrong arithmetic error in working out rate if the error is outside + or − units in third decimal place
      • Where only temperature raedings are given, penalize fully(award 0 mark) for complete table and award accordingly for decimal place and trend
        Note
      • Reject rate in fractions and strange values and penalize ½ mark for each entry upto a maximum of 1½ marks
      • Accept ¹/_t / rate given in standard form or powers of 10
      • If fractions appear followed by a decimal points ignore the fractions and mark accordingly
      • Where the values are constant in time column award a maximum of ½ mark for complete table
      • When two sets of values for temperature, time and rates are given award only ½ mark for complete table, for trend and accuracy each of the two values must meet the criteria.
   2. USE OF DECIMALS.............1 mark
      • Tied to time ½ mark and temperature ½ mark column only subject to atleast two readings in each case
        Conditions
      • Accept whole numbers, one or 2 decimal place used for time column used consistently, otherwise penalise ½ marks
      • Accept for decimals give as whole number or one decimal place of .0 or 0.5 or two decimal place of 0.00, 0.25, 0.50 or 0.75 used consistently otherwise penalize ½ mark
   3. ACCURACY.......................... 1 mark
      
      • Tied to time column omly for expweriment numbr one, compare the candidate value with the school value if within the range of + or − 2 used consistently otherwise penalize ½ mark
3. If the experiment was repeated using 5cm³ of potassium iodide solution A, determine;
   1. Volume of distilled water that would be used. (1 mark)
      14 − 5 = 9 cm³
   2. Time taken for blue colour to appear. (2 marks)
      Shown on graph 
      1/t = 0.008 sec
          t = 125 sec
4. Explain how rate of reaction is affected by the volume of potassium iodide. (2 marks)
   • Rate increases with increase in volume of KI this is because increse in volume results to increase in concentration
5. Explain why it is necessary to record the temperature each experiment. (1 mark)
   • Rate of reaction also depends on tempearture which remains constant

QUESTION 2

You are provided with solid F. Carry out the following tests and record your observations and inferences in the space provided.

1. Place all solid F into a boiling tube. Add about 10cm3 of dilute nitric (V) acid, warm the mixture and then allow it to stand until all the solid dissolves. Add about 10cm3 of distilled water to the solution and shake. Retain the solution for tests (b) and (c)
   

   observations	Inferences
   - Balck soild dissolves forming blue solution    - No effervescence                                                                                          (2 marks)	- F is a base    - CO32− or S032− Absent                                                            (1 mark)

2. Use 2cm³ portion of solution obtained in 2(a) for each of the following tests.
   1. To first portion, add 3 drops of Barium Nitrate.
      

      observations	Inferences
      - No white precipitate                                                                            (1 mark)	- SO42− Absent      -  Ignore SO32− or CO32− if mentioned                             (1 mark)

   2. To the second portion, add 3 drops of lead (ii) Nitrate solution.
      

      observations	Inferences
      - No white precipitate                                          (1 mark)	- Cl−  Absent        - Ignore if mentioned          SO32−, CO32−, SO42–                                                              (1 mark)

   3. To the third portion, add drops of 2MNaOH until in excess.
      

      observations	Inferences
      - Blue precipitate     -  Insoluble in excess                                                                                    (1 mark)	- Cu2+   Present                                                                                                           (1 mark)

   4. To the fourth portion, add few then excess drops of 2MNH₄OH provided in the access point.
      

      observations	Inferences
      - Blue precipiate the dissolved forming deep blue                         solution                                    (1 mark)	Cu2+                                                                           (1 mark)

3. To the last portion in the boiling tube add all solid G provided. Shake the mixture for about 2 minutes. Filter the mixture into a boiling tube. Retain the filtrate for test below.
   

   observations	Inferences
   - Colorless or light green filtrate   - Brown residue                                                          (1 mark)	- Metral G displaces Cu2+ or G is above Cu in                    reacting                                       (1 mark)

   
   
   1. To about 2cm³ of filtrate add few then excess drops of 2MNaOH.
      

      observations	Inferences
      - Green precipitate insoluble in                 exess                                      (1 mark)	Fe2+ present                                                                                                (1 mark)

   2. To about 2cm³ portion of filtrate add 3 drops of hydrogen peroxide solution then excess drops of 2MNaOH.
      

      observations	Inferences
      - Effervescence   - Brown precipitate                                             (1 mark)	- Fe2+ oxidised to Fe3+                                                                                                              (1 mark)

Question 3

You are provided with solid H carry out the following tests and record the observations and inferences in the space provided.

1. Place all solid in a boiling tube then add about 10cm3 of distilled water use the mixture for tests (i) and (ii) below
   

   observations	Inferences
   - Solid dissolved forming colourless solution               (1 mark)	- H is polar// Mcr    - organic substance                                               (1 mark)

   
   
   1. Using about 2cm³ of the mixture in a test tube, determine the pH using universal indicator and pH chart.
      

      pH	Inferences
      -  PH 3                                                                    (1 mark)	- strongly acidic                                                                                                     (1 mark)

   2. To about 2cm³ of the mixture in a test tube, add 3 drops of potassium manganate VII provided in the access.
      

      observations	Inferences
      - Purple acidified potasssium managate (vii) changes to                 colorless                                           (1 mark)	Ι      Ι          − C ≡ C −          C  = C                     Ι       Ι          OR    R−OH     present (1 mark)