| Date | May 2017 | Marks available | 1 | Reference code | 17M.3.sl.TZ1.3 |
| Level | SL | Paper | 3 | Time zone | TZ1 |
| Command term | Suggest | Question number | 3 | Adapted from | N/A |
Question
A class was determining the concentration of aqueous sodium hydroxide by titrating it with hydrochloric acid, whilst monitoring the pH of the solution. The sodium hydroxide solution was added into a glass beaker from a measuring cylinder and the hydrochloric acid added using a burette. One group of students accidentally used a temperature probe rather than a pH probe. Their results are given below.
Volume of aqueous NaOH = 25.0 ± 0.5 cm3
Concentration of HCl = 1.00 ± 0.01 mol dm−3
Suggest how the end point of the titration might be estimated from the graph.
Markscheme
volume «found by extrapolation of the two best fit lines» required to give the highest temperature
OR
extrapolate «two best fit» lines to the point where they meet
Accept “where lines through the points meet”.
Accept “at maximum temperature”.
Accept “at 35 cm3 of HCl”.
[1 mark]
