Question 1
| Run | Rough | 1 | 2 | 3 |
|---|---|---|---|---|
| Titre / cm³ | 25.4 | 24.8 | 25.3 | 24.9 |
A pupil's titres are shown in the table. Titres within 0.2 cm³ of each other are concordant. What average titre should be used in the calculation?
How to answer experiment questions
Many Section 2 questions are set around an experiment: a method and a set of results. They ask about the apparatus, the variables, how reliable the results are, what they show and how to improve the method.
| Where | Throughout Section 2 |
|---|---|
| Asks about | Apparatus, variables, results, conclusions |
| Techniques | Titration, filtration, collecting gases, flame tests and more |
| Here | One experiment question in every section |
What the questions ask
- Apparatus: name the piece that measures a volume accurately, collects a gas or follows a reaction, and say why it suits the job.
- Variables: the one the method changes, the one it measures, and the ones it must keep the same for a fair test.
- Reliability: repeat the experiment and average results that agree; in a titration, average only concordant titres, within 0.2 cm³ of each other.
- Results and conclusions: process the data (an average, a rate, a concentration), then say what it shows and only what it shows.
- Improvements: a change that makes the result more accurate or more reliable, with the reason.
What earns the marks
Exact observations and named apparatus earn marks where vague words do not: say the solution turns from pink to colourless, not that it changes colour. Mia reads your answer against the mark points and tells you which your answer shows and what to add next.
Try 2 questions
Question 2
| Time / s | Volume of hydrogen / cm³ |
|---|---|
| 0 | 0 |
| 20 | 48 |
| 40 | 78 |
| 60 | 90 |
| 80 | 90 |
A pupil adds magnesium ribbon to dilute hydrochloric acid and collects the hydrogen in a gas syringe. The table shows the results. What is the average rate of the reaction between 20 s and 40 s?
Next step
Questions people ask
Which techniques do experiment questions use?
Those the course lists in chemical analysis and across the sections: titration, filtration, evaporation, heating, collecting gases, flame tests, precipitation and methods of following a reaction.
What makes a result reliable?
Repeating the experiment and getting results that agree. In a titration, the titres you average should be concordant, within 0.2 cm³ of each other.