How to Write a Chemistry Lab Report

A lab report is how scientists tell other people what they did, what they found, and how much to trust it. A good one lets a reader repeat your experiment exactly and judge your conclusions for themselves. A poor one leaves them guessing. Whether you’re writing up a school practical, a coursework investigation or a university experiment, the same structure applies.

This guide walks through each section, explaining what goes in it and why.

The standard structure

1. Title
2. Aim (and hypothesis, if appropriate)
3. Introduction or background (for longer reports)
4. Risk assessment
5. Equipment and materials
6. Method
7. Results
8. Analysis (calculations and graphs)
9. Evaluation
10. Conclusion
11. References (if you used sources)

Short school write-ups may combine some sections; longer investigations and university reports usually include all of them. Always check what your teacher or course requires.

1. Title

Specific and informative. “Titration” is too vague. “Determining the concentration of ethanoic acid in vinegar by titration with sodium hydroxide” tells the reader exactly what the report is about.

2. Aim and hypothesis

Aim: one or two sentences saying what you set out to find. To determine the concentration of ethanoic acid in a sample of white vinegar.

Hypothesis: a testable prediction, ideally with a reason, used when the experiment investigates a relationship. If the concentration of hydrochloric acid is increased, the rate of reaction with magnesium will increase, because there will be more frequent collisions between acid particles and the magnesium surface.

See independent, dependent and control variables for more on identifying what you’re changing and measuring.

3. Background (optional for short reports)

A short explanation of the chemistry behind the experiment: the reaction, any equations, and why the method works. For a vinegar titration, you might write the equation CH₃COOH + NaOH → CH₃COONa + H₂O and explain why phenolphthalein is the right indicator.

Write in your own words and cite any sources you use.

4. Risk assessment

A table of hazards, risks and control measures. See how to write a risk assessment.

5. Equipment and materials

A list of what you used, with sizes and concentrations: “25.00 cm³ volumetric pipette”, “0.100 mol/dm³ sodium hydroxide solution”, “50.00 cm³ burette”, not just “pipette” and “NaOH”.

6. Method

The method should let someone else repeat your experiment exactly.

• Write numbered steps in a logical order.
• Include quantities, concentrations, volumes and times.
• State which equipment is used for each measurement.
• Mention how you controlled variables and ensured accuracy (for example, “rinsed the burette with sodium hydroxide solution”, “repeated until concordant titres were obtained”).
• Use the passive voice and past tense in formal reports: “25.00 cm³ of diluted vinegar was pipetted into a conical flask”, rather than “I pipetted”. Some teachers accept first person; follow your guidance.
• Don’t include results in the method.

A labelled diagram can replace a lot of words for apparatus set-ups.

7. Results

Present raw data clearly, usually in a table:

• Give the table a title.
• Put units in the column headings, not in every cell: “Volume / cm³” or “Volume (cm³)”.
• The independent variable goes in the first column.
• Record every measurement to the precision of the instrument: burette readings to two decimal places (23.40, not 23.4); a 0.01 g balance to two decimal places.
• Include repeats, and identify any anomalous results (and say why you’ve excluded them, if you have).
• Record qualitative observations too: colour changes, fizzing, temperature changes, precipitates.

Example:

	Rough	1	2	3
Final burette reading / cm³	21.40	21.05	42.00	21.85
Initial burette reading / cm³	0.00	0.25	21.05	1.00
Titre / cm³	21.40	20.80	20.95	20.85

8. Analysis

This is where you process the data.

Calculations: show every step clearly with units, so a reader can follow and check them. State the equation used at each stage. Give final answers to an appropriate number of significant figures.

Graphs: when investigating a relationship, plot a graph. See drawing good graphs. A good graph has:

• a title
• the independent variable on the x-axis, the dependent variable on the y-axis
• axis labels with units
• sensible, evenly spaced scales that use most of the grid
• points plotted accurately (crosses or small dots)
• a line or smooth curve of best fit (not dot-to-dot)
• anomalous points circled

Describe the pattern in words, with data: “As the concentration increased from 0.5 to 2.0 mol/dm³, the time taken for the reaction decreased from 120 s to 30 s.”

9. Evaluation

This is often the section that separates good reports from excellent ones. It should be honest and specific.

Uncertainty: calculate the percentage uncertainty in key measurements and in the final result. See calculating percentage uncertainty.

Errors: identify the main sources of error and state whether each is:

• random (varies unpredictably; reduced by repeating), or
• systematic (pushes results one way; not reduced by repeating).

Say what effect each error had on the result (too high or too low), and why.

Comparison with an accepted value: calculate the percentage error, and compare it with your percentage uncertainty. If the error is larger than the uncertainty, systematic errors are likely.

Improvements: suggest specific, realistic changes and explain how each would improve the result. “Be more careful” isn’t a valid improvement. “Use a digital thermometer reading to ±0.1 °C instead of one reading to ±0.5 °C, which would reduce the percentage uncertainty in ΔT from 15% to 3%” is.

10. Conclusion

A short answer to your aim, supported by data:

The concentration of ethanoic acid in the vinegar was 0.833 ± 0.009 mol/dm³ (5.00% w/v), consistent with the manufacturer’s stated value of 5%.

If you had a hypothesis, say whether the results support it. Avoid saying results “prove” a hypothesis; experiments provide evidence, not proof.

11. References

List any sources you used for background information or data, in the format your course requires.

Writing style tips

• Be concise and precise. Every sentence should add information.
• Use correct scientific vocabulary: “precipitate”, “titre”, “concordant”, “anomalous”, “systematic error”.
• Use SI units and correct symbols: cm³, mol/dm³, °C, g.
• Avoid vague words like “a lot”, “stuff” and “went wrong”.
• Write in paragraphs for discussion sections, not bullet points (unless your course prefers them).

Common mistakes

• Method not detailed enough to repeat.
• Units missing from table headings or graph axes.
• Inconsistent decimal places in results.
• Calculations with no working shown.
• Evaluation that lists “human error” without saying what it was or how it affected the result.
• Conclusion that doesn’t answer the aim or doesn’t quote the result.

A fully worked example of a complete report is in chemistry lab report: an annotated example.

Key takeaways

• Follow a clear structure: title, aim, method, results, analysis, evaluation, conclusion.
• Methods must be repeatable, with quantities, concentrations and equipment sizes.
• Results tables need units in headings and consistent precision.
• Analyse with clear calculations and well-drawn graphs.
• Evaluate honestly: uncertainties, random vs systematic errors, and specific improvements.