A group of students investigated the reaction between magnesium ribbon and dilute hydrochloric acid:
Mg(s)+2HCl(aq)→MgCl2(aq)+H2(g) \text{Mg}(s) + 2\text{HCl}(aq) \rightarrow \text{MgCl}_2(aq) + \text{H}_2(g) Mg(s)+2HCl(aq)→MgCl2(aq)+H2(g)They wanted to determine how changing the concentration of hydrochloric acid affects the rate of reaction. The teacher provided a stock solution labelled 100% hydrochloric acid.
All experiments were performed at room temperature by timing how long it took to collect 40 cm3 of hydrogen gas.
The students kept the amount of magnesium constant by using exactly 3 strips of magnesium ribbon in each experiment. State two other physical properties of the magnesium ribbon that should be kept constant in each experiment.
The table below shows what each student wrote down in their lab notebook:
Identify the missing piece of information that each student (B, C, D, and E) failed to record.
The students repeated the experiment using a different supply of hydrochloric acid. Their results are shown in the table below:
| Percentage concentration of hydrochloric acid (%) | Time to collect 40 cm3 of gas (s) | Rate of reaction (cm3/s\text{cm}^3/\text{s}cm3/s) |
|---|---|---|
| 10 | 100.0 | 0.40 |
| 30 | 27.6 | 1.45 |
| 50 | 25.0 | 1.60 |
| 70 | 18.2 | 2.20 |
| 90 | 14.3 | 2.80 |
| 100 | 12.9 | 3.10 |
Identify which concentration has an anomalous rate of reaction.
Suggest two experimental errors that could have caused this anomalous result.
Using a linear best-fit trend for the other five data points, estimate the rate of reaction at an acid concentration of 60%.
