DP Chemistry (last assessment 2024)
Question 19M.3.hl.TZ2.a
| Date | May 2019 | Marks available | [Maximum mark: 3] | Reference code | 19M.3.hl.TZ2.a |
| 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.a
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.
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.
