Writing Conclusions from Data in IGCSE Chemistry
How to write conclusions from experimental data in IGCSE Chemistry 0620. The structure that earns marks on Papers 4 and 6.
Published by IGCSEChemistry.com.my
Chemistry teaching team: K. S. Tan (15+ years teaching IGCSE Chemistry) and Ms Yash (10+ years teaching IGCSE Chemistry) and Ms Kartini (15+ years teaching IGCSE Chemistry).
Mapped to Cambridge IGCSE Chemistry 0620 (2026–2028). Last updated 2026-08-19.
Conclusions appear in two places on 0620: at the end of Paper 4 data-response questions and in Paper 6 evaluations. In both cases, the mark scheme is looking for the same thing — a statement that goes beyond the raw data to answer a question or describe a relationship, backed by evidence. Students who write conclusions that merely repeat the data lose marks that are available for minimal extra effort.
The three-part conclusion structure
A conclusion that earns full marks includes three elements:
1. State the relationship or pattern
This is the claim your data supports. It answers the experimental question.
“As temperature increases, the rate of reaction increases.” “The more reactive metal produces a greater temperature rise.” “Substance A is an ionic compound.”
2. Support with specific data
Quote numbers from your results or the given data.
“The rate at 40 degrees C was 2.5 cm3/s compared to 1.0 cm3/s at 20 degrees C.” “Magnesium produced a temperature rise of 25 degrees C while zinc produced only 12 degrees C.”
3. Link to the chemistry (where asked)
Connect the pattern to the scientific explanation.
“This is because at higher temperatures, particles have more kinetic energy and collide more frequently with sufficient energy to react.” “This is consistent with magnesium being higher in the reactivity series than zinc.”
Not every conclusion question requires the chemistry link, but when it is available, it differentiates a strong answer from a basic one.
Conclusion vs summary of results
Students often confuse these. Here is the difference:
| Summary of results (descriptive) | Conclusion (analytical) |
|---|---|
| “At 20 degrees C, 25 cm3 of gas was produced. At 40 degrees C, 50 cm3 was produced." | "Increasing the temperature doubles the volume of gas produced, suggesting the rate of reaction increases with temperature." |
| "The solution turned blue." | "The presence of Cu2+ ions was confirmed by the blue colour of the solution." |
| "The mass decreased over time." | "The decreasing mass indicates that a gas was produced and escaped, consistent with the decomposition of the carbonate.” |
The summary lists what happened. The conclusion says what it means.
Writing conclusions for different question types
Rate of reaction experiments
State the factor tested and its effect on rate, with data.
“Increasing the concentration of hydrochloric acid from 0.5 to 2.0 mol/dm3 increased the initial rate from 0.8 to 3.2 cm3/s. This supports the idea that higher concentration leads to more frequent collisions between reactant particles.”
Identifying unknown substances
State what the substance is, based on the test results.
“The substance produces a lilac flame colour, a white precipitate with sodium hydroxide that is insoluble in excess, and does not react with dilute acid. The results are consistent with the substance being a potassium compound.”
Comparing substances
State which substance gave the higher/lower value and what this indicates.
“Metal A produced a greater temperature rise (32 degrees C) than metal B (18 degrees C) when reacted with the same acid, suggesting metal A is more reactive than metal B.”
Paper 6 planning conclusions
In planning questions, you may be asked what conclusion you would draw from specific outcomes. Use the “if… then…” structure.
“If the temperature rises when the salt dissolves, the dissolving process is exothermic. If the temperature falls, it is endothermic.”
Common conclusion errors
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Restating the aim instead of answering it. “We were trying to find the effect of temperature on rate” is the aim, not the conclusion. “Higher temperature increases the rate” is the conclusion.
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Making claims the data does not support. If you tested only two temperatures, you cannot conclude “the rate is directly proportional to temperature.” You can conclude “the rate was higher at the higher temperature.” Proportionality requires a graph showing a straight line through the origin.
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Ignoring anomalous data. If one data point does not fit the trend, acknowledge it: “All results supported the trend except the result at 30 degrees C, which may have been affected by incomplete mixing.”
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Writing a conclusion without data. A conclusion that says “the rate increases” without any numbers is weaker than one that includes specific values.
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Over-generalising. Your conclusion should be limited to what your data shows. “All acids react faster at higher temperatures” is too broad. “Hydrochloric acid reacted faster with magnesium at 40 degrees C than at 20 degrees C” is appropriately specific.
Worked exam question
Q (Paper 6): The student investigated the effect of surface area on the rate of reaction between calcium carbonate and dilute hydrochloric acid. The results are shown in the table.
| Form of CaCO3 | Time to collect 50 cm3 of gas (s) |
|---|---|
| Large chips | 120 |
| Small chips | 68 |
| Powder | 15 |
Write a conclusion for this experiment. (2 marks)
Model answer: Decreasing the size of the calcium carbonate pieces (increasing the surface area) decreases the time taken to collect 50 cm3 of gas, meaning the rate of reaction increases (1). The powder (15 s) reacted approximately 8 times faster than the large chips (120 s), showing that surface area has a significant effect on the rate (1).
The two marks: stating the relationship (1) and supporting with specific data (1). Writing “smaller pieces react faster” without data earns only 1 mark.
If writing conclusions is costing marks, the issue is usually about going beyond the data description to state its meaning. A trial lesson can practise this skill on real experimental data.