TL;DR:
A lab report lets another person understand and repeat what you did, so be specific.
Use past tense for what you did and present tense for what the results show.
Put units in table headings and tie your discussion back to the aim.
You ran the experiment, wrote numbers in your notebook and now have to turn them into a report. The report is not a diary. It is a record that lets a stranger understand what you tested, check what you found and run it again. A standard structure makes that easy to do.
The sections and what each does
Title. Says what was measured against what.
Aim (or question). One sentence on what you wanted to find out. Many teachers also want a hypothesis.
Method. What you did, in enough detail to repeat it, including equipment and what you controlled.
Results. Your data in a table, plus a graph if asked, with units. No explanation yet.
Discussion. What the results mean, whether they support the hypothesis, what went wrong and what you would improve.
Conclusion. The answer to the aim, in a sentence or two.
Your teacher may rename or reorder sections, so follow the assignment sheet. The purpose stays the same.
Worked example: a lab on reaction rates
The experiment: how does water temperature change how fast an effervescent tablet dissolves? The numbers below are an example, not real results.
Title. The effect of water temperature on the time for an effervescent tablet to dissolve.
Aim. To find how the temperature of 200 mL of water affects the time a tablet takes to stop fizzing. Hypothesis. The tablet will dissolve faster in warmer water, because particles move faster and collide more often.
Method (past tense, impersonal). Three 200 mL samples of water were measured with a measuring cylinder and brought to 10 °C, 20 °C and 40 °C. The temperature was checked with a thermometer. One tablet of the same brand was dropped into each sample, and a stopwatch recorded the time until the fizzing stopped. The volume, the brand and the beaker were kept the same. Each trial was repeated once.
Results. Present the data first, with units in the headings.
Temperature (°C) | Time to dissolve (s) | Rate, 1 ÷ time (s⁻¹) |
|---|---|---|
10 | 90 | 0.011 |
20 | 60 | 0.017 |
40 | 25 | 0.040 |
Check the last column: 1 ÷ 90 = 0.0111, 1 ÷ 60 = 0.0167, 1 ÷ 25 = 0.0400. A shorter time means a faster rate, so turning time into 1 ÷ time makes the trend go up as the temperature goes up, which is easier to read on a graph.
Discussion (present tense for what the data show). The time falls from 90 s to 25 s as the temperature rises from 10 °C to 40 °C, so the rate rises. This supports the hypothesis. A possible explanation is that particles in warmer water move faster, so they collide more often and with more energy. Sources of error include judging when the fizzing stopped by eye, small differences between tablets and heat lost to the air while the water was being measured. Repeating each trial three times and averaging would reduce the effect of one slow reading.
Conclusion. Within the range tested, a higher water temperature shortened the time for the tablet to dissolve.
Tense and voice
Describe what you did in the past tense: "The water was heated." Many science teachers prefer the passive voice there, because the person does not matter. State what the data show, and general science facts, in the present tense: "The rate increases with temperature."
Units and tables
Give every column a heading with its unit, such as
Time (s).Keep the same number of decimal places within a column, and match the precision of your instrument.
Title tables and graphs, and label graph axes with quantity and unit.
Never leave a bare number. "25" means nothing; "25 s" does.
Safety: Follow your teacher's safety instructions in the lab. Wear eye protection when you work with chemicals, and report spills at once.
Writing the discussion well
The discussion is where marks are usually won or lost. Follow a simple order: state the trend in your data with numbers, say whether it matches the hypothesis, offer a scientific reason, and then evaluate your method. Each step is one or two sentences.
When you name an error, make it specific and say which way it pushed the results. "The timer was started a moment late, so recorded times were slightly too short" is useful. "Mistakes may have happened" is not. Then add what you would change, such as using a gas syringe or a digital probe instead of judging by eye.
Finally, check that your discussion answers the aim. If the aim asked how temperature affects time, the last sentence of the discussion should say how.
Mistakes to avoid
Mixing results and explanation. Keep data in Results and meaning in Discussion.
Claiming "proves". A single experiment supports a hypothesis, it rarely proves it.
Writing "human error" without saying what the error was and how it changed the result.
Leaving out the control variables, which the reader needs to repeat your work.
Your plan for this week
Before you write, draw the empty results table and the axes of your graph on a page. It tells you what you still need to record, and it keeps the report focused. Then write the sections in this order: method, results, discussion, aim and title last, since you then know exactly what the report did.
Frequently asked questions
Do I need a hypothesis?
Many classes do. If yours does, state it before the method and say whether the results support it in the discussion.
How long should the discussion be?
Long enough to explain the trend, name specific errors and suggest one or two improvements. Quality matters more than length.
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