How to write a lab report

A lab report has a fixed structure for a reason: another scientist should be able to read your method, repeat exactly what you did, and get the same result. Everything about the conventions — the tense, the impersonal voice, the obsessive detail about equipment — follows from that single requirement.

Marks are lost in predictable places. Almost always in the discussion, and almost always because the writer described the results a second time instead of explaining them.

The sections

Title. Specific and informative. "The effect of temperature on the rate of catalase activity in potato tissue", not "Enzyme experiment".

Abstract. 150–250 words, written last. Aim, method in one line, key result with the number, conclusion. Someone should be able to read only this and know what happened.

Introduction. The background theory, narrowing to your specific question. End with your aim and, where relevant, your hypothesis stated as a prediction that could be wrong.

Method. What you actually did, in the past tense, in enough detail to repeat. Not a bulleted list of instructions copied from the handbook — continuous past-tense prose describing what was done. Include concentrations, volumes, temperatures, timings, equipment and model numbers where they matter.

Results. Data, presented and described, with no interpretation. Tables and graphs numbered and captioned. Every figure needs axis labels with units. Write a short paragraph pointing the reader at what the data shows: "Rate increased with temperature to a maximum of 0.42 cm³ s⁻¹ at 40 °C, then fell sharply."

Discussion. The section that carries the marks. Explain why the results came out that way, using the theory from your introduction. Compare with what was expected. Account for anomalies. Evaluate the method honestly — what limited the reliability, and what would you change. Do not simply restate the numbers.

Conclusion. Two or three sentences answering the aim.

References. In your department's style.

Tense and voice

• Introduction: present tense for established science ("catalase breaks down hydrogen peroxide").
• Method and results: past tense ("the solution was heated to 60 °C").
• Discussion: present tense for what your results show, past for what you did.

Most science departments still expect the impersonal passive in the method — "the mixture was stirred" rather than "I stirred the mixture". A growing number of journals and some departments now prefer the active first person. Check your own handbook; this is one of the few places where following the local rule matters more than following good general writing advice.

Uncertainty and significant figures

Report values to the precision your instrument actually justifies. A balance reading to 0.01 g does not license an answer to five decimal places, and writing one signals that you do not understand your own data.

State uncertainties where the course expects them, and carry them through calculations rather than adding them at the end. If you did repeats, report the mean and a measure of spread — not just the mean.

Common mistakes

Copying the method from the handbook in the imperative ("add 10 ml of..."). Interpreting results inside the results section. Restating results inside the discussion instead of explaining them. Graphs without axis units. Claiming human error as the explanation for everything — it is almost never the dominant source, and naming a specific systematic limitation earns marks that "human error" does not. Concluding something your data does not support. Writing the abstract first.

Practical tips

• Write the method the same day you do the practical, while you still remember what actually happened rather than what was supposed to.
• Draft the results and discussion before the introduction; you will know what background the reader needs.
• For every anomaly, write one sentence saying what could physically have caused it.
• Check the marking rubric before you submit. Lab reports are usually marked against an explicit checklist, and it tells you where the marks are.