DP Chemistry (last assessment 2024)
Question 19M.3.hl.TZ2.2a
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.3.hl.TZ2.2a |
| Level | hl | Paper | 3 | Time zone | TZ2 |
| Command term | Determine | Question number | a | Adapted from | N/A |
a.
[Maximum mark: 3]
19M.3.hl.TZ2.2a
Bromine and methanoic acid react in aqueous solution.
Br2 (aq) + HCOOH (aq) → 2Br− (aq) + 2H+ (aq) + CO2 (g)
The reaction was monitored by measuring the volume of carbon dioxide produced as time
progressed.
(a)
Determine from the graph the rate of reaction at 20 s, in cm3 s−1, showing your working.
[3]
Markscheme
tangent drawn to curve at t = 20 s [✔]
slope/gradient calculation [✔]
0.35 «cm3 s–1» [✔]
Note: Accept values in the range 0.32–0.42 «cm3 s–1»
Examiners report
This part proved to be challenging for some candidates whereas other candidates were able to draw a tangent at 20 sec and then calculate the rate. A significant number of candidates calculated the average rate and achieved one mark.
