CSEE
Chemistry · Paper 2B · 2020
3 questions 🇹🇿 NECTA ✓ Official NECTA answers
CSEE
🇹🇿 NECTA
✓ Official NECTA answers
Chemistry · Paper 2B · 2020
3 questions
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Questions (3)
Section A
2.
25 marks
Study the reaction between sodium thiosulphate and hydrochloric acid. The chemicals provided are labelled as N1, N2, and N3 for 0.13 M sodium thiosulphate, 2.0 M hydrochloric acid and distilled water respectively. You are also provided with a piece of white paper marked X on which a 100 cm3 beaker containing the reaction mixture. Mix volumes of N1, N2, and N3 and at the same time record the time taken for the reaction as shown in the following table.
| Volume of N1 (cm3) | Volume of N3 (cm3) | Volume of N2 (cm3) | Time (s) |
|---|---|---|---|
| 2 | 8 | 10 | |
| 4 | 6 | 10 | |
| 6 | 4 | 10 | |
| 8 | 2 | 10 | |
| 10 | 0 | 10 |
(a)
Record the time taken for each experiment in the table provided.
5 mk
(a)
Complete filling the table.
0 mk
(b)
Calculate the rate of reaction in each experiment.
5 mk
(b)
(i) plot a graph of volume N1 (vertical axis) against time (horizontal axis) taken for the letter X to disappear completely.
(ii) comment on the shape of the graph.
0 mk
(c)
Plot a graph of Rate of reaction (y-axis) against Volume of N1 (x-axis).
8 mk
(c)
Explain why did the letter X disappear.
0 mk
(d)
Explain the shape of the graph in relation to the rate of reaction.
7 mk
(d)
Write the electronic configuration of the product which causes the solution to be cloudy (milky).
0 mk
(none)
Explain the trend observed in the graph.
5 mk
(e)
Write the ionic equation for the reaction between N1 and N2.
0 mk
(f)
Explain why N3 was added to N1.
0 mk
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