Some students design an experiment to investigate the effect of hydrogen peroxide concentration on the rate of oxygen production by the enzyme catalase. The apparatus collected oxygen gas in a gas syringe.
Method:
Some of the results are shown in the tables below:
Table 1: Results for 5%5\%5% hydrogen peroxide
| Time (s) | Trial 1 (cm3\text{cm}^3cm3) | Trial 2 (cm3\text{cm}^3cm3) | Trial 3 (cm3\text{cm}^3cm3) | Mean (cm3\text{cm}^3cm3) | Standard deviation |
|---|---|---|---|---|---|
| 20 | 12 | 14 | 13 | 13.0 | 1.0 |
| 40 | 23 | 25 | 24 | 24.0 | 1.0 |
| 60 | 32 | 35 | 32 | 33.0 | 1.7 |
| 80 | 40 | 41 | 39 | 40.0 | 1.0 |
Table 2: Results for 25%25\%25% hydrogen peroxide
| Time (s) | Trial 1 (cm3\text{cm}^3cm3) | Trial 2 (cm3\text{cm}^3cm3) | Trial 3 (cm3\text{cm}^3cm3) | Mean (cm3\text{cm}^3cm3) | Standard deviation |
|---|---|---|---|---|---|
| 20 | 25 | 23 | 24 | 24.0 | 1.0 |
| 40 | 46 | 40 | 46 | 44.0 | [ To be calculated ] |
| 60 | 61 | 58 | 61 | 60.0 | 1.7 |
| 80 | 72 | 68 | 70 | 70.0 | 2.0 |
(i) State the independent variable in this investigation. (ii) Describe how a student could produce a 15%15\%15% dilute hydrogen peroxide solution from the 25%25\%25% stock solution.
(i) Calculate the standard deviation for the 40 s40\text{ s}40 s result at 25%25\%25% hydrogen peroxide. Use the formula:
s=∑(x−xˉ)2n−1 s = \sqrt{\frac{\sum(x - \bar{x})^2}{n - 1}} s=n−1∑(x−xˉ)2Give your answer to 1 decimal place. (ii) Calculate the initial rate of reaction over the first 20 s20\text{ s}20 s for the result at 5%5\%5% hydrogen peroxide. Include the appropriate unit.
