Question 19M.3.sl.TZ1.b(ii)
| Date | May 2019 | Marks available | [Maximum mark: 1] | Reference code | 19M.3.sl.TZ1.b(ii) |
| Level | sl | Paper | 3 | Time zone | TZ1 |
| Command term | Suggest | Question number | b(ii) | Adapted from | N/A |
Powdered zinc was reacted with 25.00 cm3 of 1.000 mol dm−3 copper(II) sulfate solution in an insulated beaker. Temperature was plotted against time.
To determine the enthalpy of reaction the experiment was carried out five times. The same volume and concentration of copper(II) sulfate was used but the mass of zinc was different each time. Suggest, with a reason, if zinc or copper(II) sulfate should be in excess for each trial.
[1]
Any one of:
copper(II) sulfate AND mass/amount of zinc is independent variable/being changed.
OR
copper(II) sulfate AND with zinc in excess there is no independent variable «as amount of copper(II) sulfate is fixed» [✔]
copper(II) sulfate AND having excess zinc will not yield different results in each trial [✔]
zinc AND results can be used to see if amount of zinc affects temperature rise «so this can be allowed for» [✔]
zinc AND reduces variables/keeps the amount reacting constant [✔]
The correct answer depended on whether students considered the object of the additional trials was to investigate the effect of a new independent variable (excess copper(II) sulphate) or to obtain additional values of the same enthalpy change so they could be averaged (excess zinc). Answers that gave adequate reasons were rare.
