Some students investigated the rate of reaction between sodium thiosulfate solution and dilute hydrochloric acid. The equation for the reaction is:
Na2S2O3(aq)+2HCl(aq)→2NaCl(aq)+H2O(l)+S(s)+SO2(g) \text{Na}_2\text{S}_2\text{O}_3(\text{aq}) + 2\text{HCl}(\text{aq}) \rightarrow 2\text{NaCl}(\text{aq}) + \text{H}_2\text{O}(\text{l}) + \text{S}(\text{s}) + \text{SO}_2(\text{g}) Na2S2O3(aq)+2HCl(aq)→2NaCl(aq)+H2O(l)+S(s)+SO2(g)The precipitate of sulfur makes the reaction mixture go cloudy.
The students used the following method:
The students used 10 cm310\text{ cm}^310 cm3 of dilute hydrochloric acid in each experiment. They carried out all the experiments at the same temperature. They used different volumes of sodium thiosulfate solution and water in each experiment, aiming to keep the total volume of sodium thiosulfate solution and water constant.
The table shows their results:
| Student | Volume of sodium thiosulfate solution in cm3\text{cm}^3cm3 | Volume of water in cm3\text{cm}^3cm3 | Time in s\text{s}s |
|---|---|---|---|
| 1 | 40 | 0 | 18.4 |
| 2 | 30 | 10 | 25.2 |
| 3 | 25 | 15 | 30.8 |
| 4 | 20 | 20 | 39.5 |
| 5 | 15 | 25 | 55.1 |
| 6 | 10 | 30 | 85.3 |
| 7 | 5 | 45 | 162.0 |
Explain why the results of student 7 should not be used.
The rate of reaction can be calculated using the following equation:
rate of reaction=1000time taken \text{rate of reaction} = \frac{1000}{\text{time taken}} rate of reaction=time taken1000Calculate the rate of reaction for student 2's experiment. Give your answer to one decimal place.
Another group plotted a graph of the rate of reaction against the concentration of sodium thiosulfate. The graph shows a straight line passing through the origin (0,0)(0,0)(0,0).
Describe the relationship between the concentration of sodium thiosulfate solution and the rate of reaction shown by this graph.
Explain, in terms of collision theory, why increasing the concentration has this effect on the rate.
