Question 19M.2.sl.TZ1.b(i)
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.2.sl.TZ1.b(i) |
| Level | sl | Paper | 2 | Time zone | TZ1 |
| Command term | Determine | Question number | b(i) | Adapted from | N/A |
This question is about peroxides.
Hydrogen peroxide decomposes to water and oxygen when a catalyst such as potassium iodide, KI, is added.
2H2O2 (aq) O2 (g) + 2H2O (l)
In a laboratory experiment solutions of potassium iodide and hydrogen peroxide were mixed and the volume of oxygen generated was recorded. The volume was adjusted to 0 at t = 0.
The data for the first trial is given below.
Plot a graph on the axes below and from it determine the average rate of formation of oxygen gas in cm3 O2 (g) s−1.
Average rate of reaction:
[3]
points correctly plotted [✔]
best fit line AND extended through (to) the origin [✔]
Average rate of reaction:
«slope (gradient) of line =» 0.022 «cm3 O2 (g) s−1» [✔]
Note: Accept range 0.020–0.024cm3 O2 (g) s−1.
The graphing was disappointing with a surprising number of students missing at least one mark for failing to draw a straight line or for failing to draw the line passing through the origin. Also some were unable to calculate the gradient.