A good improvement links one limitation, one specific change and its effect on the results, and it never adds a hazard. This lesson draws on every earlier skill in practical-data interpretation, because you must recognise the variable, the readings and the apparatus to say how a result could be made more trustworthy.
How do you write an improvement, step by step?
- Pick one stated limitation. Do not list several in a single sentence.
- Decide whether it is random or systematic. This tells you whether repeating will help.
- Name a specific change. For example, use a more precise measuring instrument, use a sensor instead of judging by eye, or keep temperature steady with a water bath.
- Say the effect. The readings become more precise, more accurate or more reproducible, and explain why.
- Check the safety. The change should not increase any hazard. Leave changes to materials or conditions to a teacher.
Worked example
Invented scenario. A class times how long a cross under a beaker takes to disappear as a solution turns cloudy. The report gives three limitations: the timer was stopped by eye, the temperature fell as the beaker stood on the bench, and only five temperatures were tested.
| Limitation | Type | Specific change | Effect on results |
|---|---|---|---|
| Timer stopped by eye | Random, plus a systematic delay | Use a light sensor and data logger to detect the cross fading | Removes judgement and reaction delay, so times are more reproducible |
| Temperature fell during the test | Systematic | Keep the beaker in a water bath at the set temperature | Temperature stays closer to its stated value, so results are more accurate |
| Only five temperatures | Limits the pattern | Test more temperatures across the same range | The pattern and any anomalies are easier to see |
Each row names the limitation, the change and the benefit. None of the changes raises a hazard.
What mistake is easy to make?
Mistaken answer: “To improve the experiment, be more careful and use better equipment.”
The student named no limitation, no equipment and no effect.
This answer is general advice. It earns credit only if it says which equipment, for which problem, and what it changes. The correction is to write, for example, “use a burette instead of a measuring cylinder, because it reads to a smaller division, so the volume of acid is more precise”.
A second version of the same mistake is to rely only on repeating. Repeating and averaging reduces random scatter, but a timer started late every time still shifts every result the same way.
A short calculation to support an improvement
Invented figures. Assume a measuring cylinder has an uncertainty of ±0.5 cm³. The percentage uncertainty depends on the volume measured.
- For a 10 cm³ reading: 0.5 ÷ 10 × 100 = 5%.
- For a 25 cm³ reading: 0.5 ÷ 25 × 100 = 2%.
So measuring a larger volume, or using an instrument with a smaller uncertainty, reduces the percentage uncertainty. That gives a numerical reason to support a change.
Check yourself
1. A limitation says “some gas escaped before the bung was replaced.” Give one conceptual improvement.
Show answer
Arrange the set-up so the system is sealed before the reaction starts, for example by combining the reactants only once everything is connected. This reduces the loss of gas, so the volume measured is closer to the true value.
2. Why does “repeat the experiment three times” not fix a timer that is always started late?
Show answer
The delay is a systematic error. It affects every repeat in the same direction, so averaging does not remove it. A sensor or a different timing method is needed.
3. A reading of 20 cm³ has an uncertainty of ±0.5 cm³. What is the percentage uncertainty?
Show answer
0.5 ÷ 20 × 100 = 0.025 × 100 = 2.5%.
Where does this lead next?
The mixed practice set lets you apply every skill in this module together. For the chemistry behind the timing examples, revisit rates of reaction.
Improvement answers improve fastest when someone reads them with you and asks what the change actually does. That is one thing you can expect from online one-to-one Chemistry tuition.