2016 KCSE Chemistry Paper 3 Past Paper
1. You are provided with the following:
• Aqueous potassium iodide, solution A1
• Aqueous sodium thiosulphate, solution A2
• Acidic solution, solution A3
• Starch solution, solution A4
• Dilute hydrogen peroxide, solution B
• Distilled water
You are required to determine the rate of reaction between acidified potassium iodide and hydrogen peroxide.
Using a 10 ml measuring cylinder, place 2 cm3 of solution A1 into a MO ml beaker. Add 2 cm3 of solution A2 followed by 2 cm3 of solution A3 . Add 5 drops of solution A4. Finally, add 12 cml of distilled water and shake the mixture.
Using a burette, place 6 cm’ of solution B into a test tube.
Pour the measured 6cm3 of solution B into the beaker in Step 1 above and immediately start a stopwatch/clock.
Swirl the mixture and place on a white paper.
Observe the mixture and immediately stop the stopwatch/clock when a blue colour appears. Record the time taken in table 2.
Measure the temperature of the mixture and record in table 2.
These arc the results of experiment I.
Repeat steps 1 and 2 using the volumes of solutions given in table 1 for experiments 2, 3, 4, 5 and 6 and record in table 2.
(b) plot a graph of a late of reaction 1/time vertical axis against volume of potassium iodide (3 marks)
(c) Explain why it is necessary to record the temperature for each experiment. (1 mark)
(d) ln the experiment was repeated using 7 cm3 of acidified potassium iodide, solution AI, determine:
(i) the volume of distilled water that would be used. (1 mark)
(ii) the time taken for the blue colour to appear. (2 marks)
(e) Explain how the rate of the reaction is affected by the volume of acidified potassium iodide. (1 mark)
2. You are provided with Solution G. Carry out the following tests and record your observations i and inferences in the spaces provided.
(a) Measure the pH of the solution using 2 cm3 of Solution G and universal indicator paper.
(b) To about 2cm3 of G in a test tube, add dropwise dilute nitric (V) acid until no further change. Retain the mixture for use in tests (c)(i) and (c)(ii)
(c) Divide the mixture obtained in (b) above into two portions.
(i) To the first portion, add 3 drops of aqueous lead (II) nitrate.
(ii) To the second portion, add 3 drops of aqueous barium nitrate. observations inferences
(d) Describe a test that you would carry out to find out if Zn2+ ions are present in Solution G.
(e) Carry out the test described in (d) above.
3. You are provided with Solid H. Carry out the following tests and record your observations and inferences in the spaces provided.
(a) Place all of Solid H in a boiling tube. Add about 10 cm3 of distilled water and shake the mixture thoroughly.
To about 2cm3 of the mixture in a test tube, add about half of the solid sodium hydrogen carbonate.
(c) To the remaining amount of the mixture of H in the boiling tube add about 10 cm3 of dilute hydrochloric acid.
Shake thoroughly then filter the mixture. Wash the residue with distilled water.
Dry the residue using filter papers. Use the residue for tests (i), (ii) and (iii) below.
(i) Place about one third of the residue in a test tube. Add about 10cm3 of distilled water and warm the mixture.
To the warm mixture, add the remaining amount of solid sodium hydrogen carbonate.
(ii) To about one third of the residue in a test tube, add about 5 cm3 of distilled water, shake the mixture and then add 3 drops of bromine water.
(iii) To the remaining amount of the residue in the boiling tube, add about 10cm3 of distilled water, about 5 cm3 of dilute sulphuric (VI) acid and then about 5 cm3 of ethanol. Warm the mixture.