Question 19M.3.sl.TZ2.c(i)
| Date | May 2019 | Marks available | [Maximum mark: 2] | Reference code | 19M.3.sl.TZ2.c(i) |
| Level | sl | Paper | 3 | Time zone | TZ2 |
| Command term | Describe | Question number | c(i) | Adapted from | N/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.
Describe one systematic error associated with the use of the gas syringe, and how the error affects the calculated rate.
[2]
ALTERNATIVE 1
gas may leak/be lost/escape
OR
plunger may stick/friction «so pressure is greater than atmospheric pressure»
OR
syringe may be tilted «up» so plunger moves less «with gravity acting on plunger»
OR
CO2 dissolved in water [✔]
calculated rate lower [✔]
ALTERNATIVE 2
syringe may be tilted «down» so plunger moves more «with gravity acting on plunger»
OR
syringe is held in hand so gets warmer and gas expands [✔]
calculated rate higher [✔]
Note: Calculated rate is lower or higher must be stated for M2.
Do not accept “scale on syringe is inaccurate”, “errors in reading syringe”, or “bubbles in syringe”.
This question was asking about a systematic error. There were several possible correct answers for the error, but students also needed to clearly identify a specific error and if the rate increased or decreased for the second mark. Many students confused this with the concept of a random error and identified the uncertainty of reading the syringe which is incorrect. Teachers need to reinforce the concept of systematic versus random errors.
