Writing Scientific Lab Reports
2. Writing a Scientific Method
Learning outcomes
- I can write clear step-by-step experimental procedures.
- I can describe procedures in sufficient detail for replication.
- I can identify safety precautions within experimental methods.
- I can organize procedures logically.
- I can explain why repeatable methods are important.
What Is a Scientific Method?
In a lab report, the method or procedure explains exactly how an investigation was carried out.
It should answer the question:
What did the researcher do, and how did they do it?
A good method allows another person to repeat the investigation as closely as possible.
It should describe:
- equipment used
- quantities measured
- variables changed
- variables controlled
- measurements taken
- sequence of steps
- repeated trials
- relevant safety precautions
- how results were recorded
The method is one of the most important parts of a scientific investigation because other scientists must be able to understand and evaluate how the evidence was produced.
Why Does the Method Matter?
Imagine reading this method:
1. Get some water.
2. Add sugar.
3. Heat it.
4. See what happens.
This is not scientifically useful.
Another person would immediately have questions:
- How much water?
- How much sugar?
- What temperature?
- What container?
- How was temperature measured?
- Was the mixture stirred?
- What was measured?
- How long was it observed?
- Was the experiment repeated?
Without these details, different people could perform completely different experiments.
A Repeatable Method
A good method should be repeatable.
This means another person should be able to follow the instructions and perform essentially the same investigation.
Repeatability is important because scientific evidence becomes more useful when results can be checked.
Replication
Replication means performing an investigation again using the same or a closely matched method.
If another researcher can reproduce the procedure, they can compare their results with the original findings.
This helps scientists determine whether a result is:
- consistent
- reliable
- unusual
- affected by the original procedure
A method that cannot be understood or reproduced makes the evidence much harder to evaluate.
Characteristics of a Strong Scientific Method
A strong method should be:
- clear
- specific
- logically ordered
- measurable
- repeatable
- safe
- connected to the variables
- detailed enough for replication
- free from unnecessary information
The goal is not simply to make the method long.
The goal is to make it precise.
Organizing a Method Logically
Experimental steps should appear in the order they are performed.
A typical sequence might be:
Prepare equipment → Set starting conditions → Change independent variable → Measure dependent variable → Record data → Repeat → Change independent variable again
This creates a logical experimental cycle.
Start with the Setup
The first steps should usually explain how the apparatus is prepared.
For example:
1. Place a 250 mL beaker on a stable laboratory bench.
2. Measure 100 mL of water using a measuring cylinder and pour it into the beaker.
3. Place a thermometer into the water without allowing the bulb to touch the bottom of the beaker.
The reader can now reconstruct the experimental setup.
Use Numbered Steps
Numbered steps make a procedure easier to follow.
For example:
- Measure 50.0 mL of water using a measuring cylinder.
- Pour the water into a 100 mL beaker.
- Measure the initial temperature using a thermometer.
- Add 5.0 g of salt.
- Stir the solution for 30 seconds.
- Record the final temperature.
This is clearer than writing all instructions in one long paragraph.
Use Clear Action Verbs
Experimental methods should use precise action words.
Useful verbs include:
- measure
- record
- pour
- add
- place
- heat
- cool
- stir
- observe
- calculate
- repeat
- connect
- release
- collect
- weigh
- time
For example:
Measure 25 mL of solution.
is clearer than:
Get some solution.
Be Specific About Quantities
Compare these instructions.
Weak:
Add some water.
Strong:
Measure 100 mL of water using a measuring cylinder and pour it into the beaker.
Weak:
Add salt.
Strong:
Measure 5.0 g of sodium chloride using an electronic balance and add it to the water.
Specific quantities make the experiment easier to replicate.
Identify the Equipment
The method should explain which equipment is used when that information affects how the experiment is performed.
For example:
Measure 50 mL of water using a measuring cylinder.
is more useful than:
Measure 50 mL of water.
The reader now knows both:
what was measured
and:
how it was measured
Include Appropriate Precision
Suppose a student writes:
Measure 5 g of salt.
If an electronic balance measuring to 0.1 g is used, it may be more appropriate to write:
Measure 5.0 g of salt using an electronic balance.
The level of precision should match the equipment and investigation.
Avoid reporting precision that the equipment cannot actually provide.
Describe the Independent Variable
The method must clearly explain how the independent variable will be changed.
Suppose the investigation asks:
How does temperature affect the time required for sugar to dissolve?
The independent variable is:
water temperature
The method might test:
20°C, 30°C, 40°C, 50°C, and 60°C
These values should be stated clearly.
Use a Suitable Range
A strong investigation usually tests several values of the independent variable.
Testing only:
20°C and 60°C
provides limited information.
Testing:
20°C, 30°C, 40°C, 50°C, 60°C
allows the researcher to examine the pattern between the variables more effectively.
The chosen range and intervals should make sense for the investigation.
Describe the Dependent Variable
The method must also explain how the dependent variable will be measured.
Weak:
See how fast it dissolves.
Strong:
Start the stopwatch immediately after adding the sugar and stop it when no visible sugar crystals remain. Record the dissolving time to the nearest second.
Now the dependent variable has an operational definition.
Operational Definitions
An operational definition explains exactly how a quantity or condition will be measured or recognized.
Suppose an investigation measures:
reaction completion
What counts as complete?
Possible definition:
The reaction will be considered complete when no further gas bubbles are observed for 10 seconds.
This makes the measurement more consistent.
Another Operational Definition
Suppose students investigate:
plant growth
What does "growth" mean?
It could mean:
- change in height
- change in mass
- number of leaves
- increase in stem length
A stronger method might state:
Measure plant height from the soil surface to the highest point of the main stem using a ruler.
Now different researchers are more likely to measure the same quantity.
Include Controlled Variables
A strong method explains how important controlled variables will be kept consistent.
Suppose temperature is the independent variable in a dissolving experiment.
Controlled variables might include:
- 100 mL water each trial
- 5.0 g sugar each trial
- same type of sugar
- same beaker size
- same stirring technique
- same endpoint criterion
These details help make the investigation a fair test.
Do Not Just List Controlled Variables
It is better to explain how important variables will be controlled.
Instead of:
Control the amount of water.
write:
Measure 100 mL of water using the same measuring cylinder for every trial.
Instead of:
Keep stirring the same.
write:
Stir each solution at approximately one complete rotation per second using the same stirring rod.
The second versions describe actions another researcher can reproduce.
Include Repeated Trials
A single measurement may be affected by random variation.
A stronger method includes repeated trials.
For example:
Repeat the measurement three times at each temperature.
Then calculate:
mean = sum of measurements ÷ number of measurements
Repeated trials help reveal how consistent the measurements are.
Why Repeat Measurements?
Suppose three trials produce:
42.1 s
41.8 s
42.3 s
These results are quite consistent.
Now suppose they produce:
42.1 s
68.4 s
41.9 s
The second trial may require investigation.
Without repeated measurements, the unusual value might never be recognized.
Repetition vs Replication
These terms are related but slightly different.
Repetition usually means the same researcher repeats measurements under the same conditions.
Replication usually means an investigation is independently repeated, often by another researcher or group.
Both help scientists assess the consistency and reliability of evidence.
Recording Data
A good method should explain how results will be recorded.
For example:
Record the dissolving time for each trial in a prepared data table.
A table might include:
| Temperature (°C) | Trial 1 (s) | Trial 2 (s) | Trial 3 (s) | Mean Time (s) |
|---|---|---|---|---|
| 20 | ||||
| 30 | ||||
| 40 | ||||
| 50 | ||||
| 60 |
Planning the data table before beginning the investigation can reduce mistakes.
Include Safety in the Method
Safety should be considered while designing the experiment, not added as an afterthought.
A useful approach is:
Hazard → Risk → Precaution
For example:
Hot water → burns → use heat-resistant gloves or tongs when handling hot containers.
Safety Precautions Should Be Specific
Weak:
Be careful with the acid.
Strong:
Wear safety goggles when handling dilute hydrochloric acid and immediately rinse any splash on the skin with plenty of water.
Weak:
Be careful with heat.
Strong:
Use tongs to move heated glassware and allow it to cool on a heat-resistant mat before handling it directly.
Specific precautions are much more useful.
Safety Should Match the Actual Risk
Do not include random safety statements simply because the work takes place in a laboratory.
For example:
Wear goggles because laboratories are dangerous
is not a strong scientific risk assessment.
Instead identify:
- the actual hazard
- the possible harm
- how the risk will be reduced
Example: Heating Investigation
Suppose students are heating water.
Relevant hazards may include:
- hot water
- hot glassware
- electrical heating equipment
Appropriate precautions might include:
- wear eye protection
- keep electrical equipment away from spilled water
- handle hot containers with suitable equipment
- allow glassware to cool before touching it
Example: Force Investigation
Suppose students investigate the extension of a spring.
Potential hazards include:
- overstretching the spring
- falling masses
- unstable clamp stands
Suitable precautions might include:
- secure the clamp stand
- keep feet away from hanging masses
- do not exceed the spring's safe load
- add masses carefully
Safety depends on the specific investigation.
Diagrams Can Support a Method
Some experimental setups are difficult to explain using words alone.
A labeled diagram can show:
- position of equipment
- connections
- distances
- measurement points
- direction of forces
- location of sensors
A diagram should support the written method rather than replace it.
The written procedure should still explain what the researcher actually does.
Writing a Method Before the Experiment
In many investigations, students design the method before collecting data.
This allows them to check:
- Are the variables clearly identified?
- Can the dependent variable actually be measured?
- Is enough data being collected?
- Are important variables controlled?
- Is the experiment safe?
- Is the equipment available?
- Can another person follow the procedure?
Planning can prevent major problems before experimentation begins.
Writing a Method After the Experiment
Sometimes a lab report is written after the investigation.
In that case, the method should describe:
what was actually done
not what was originally planned if the procedure changed.
If an important change occurred, the final report should accurately reflect it.
Scientific reports must provide an honest record of the investigation.
Example Investigation: Dissolving Sugar
Research question:
How does water temperature affect the time required for 5.0 g of sugar to dissolve in 100 mL of water?
Independent variable:
water temperature
Dependent variable:
dissolving time
Important controlled variables:
- volume of water
- mass of sugar
- sugar type
- stirring method
- container
- endpoint criterion
Weak Method
1. Put water in a beaker.
2. Heat it.
3. Add sugar.
4. Stir it.
5. Time how long it takes.
6. Repeat at other temperatures.
This gives the general idea, but it cannot be replicated accurately.
Improved Method
- Measure 100 mL of water using a measuring cylinder and transfer it to a 250 mL beaker.
- Adjust the water temperature to 20°C and verify the temperature using a thermometer.
- Measure 5.0 g of sugar using an electronic balance.
- Add the sugar to the water and start the stopwatch immediately.
- Stir the mixture at approximately one complete rotation per second using a stirring rod.
- Stop the stopwatch when no visible sugar crystals remain at the bottom of the beaker.
- Record the dissolving time in seconds.
- Repeat steps 1–7 three times at 20°C.
- Calculate the mean dissolving time.
- Repeat the procedure at 30°C, 40°C, 50°C, and 60°C.
- Record all measurements in a prepared data table.
This method is much more reproducible.
Worked Example: Pendulum Investigation
Research question:
How does pendulum length affect the period of a pendulum?
A suitable method might include:
- Attach a string securely to a clamp stand.
- Attach a pendulum bob to the other end.
- Adjust the length from the pivot to the centre of the bob to 20.0 cm.
- Pull the bob to a small, consistent starting angle.
- Release the bob without pushing it.
- Measure the time for 10 complete oscillations using a stopwatch.
- Divide the measured time by 10 to calculate the period of one oscillation.
- Repeat three times.
- Calculate the mean period.
- Repeat using lengths of 40.0, 60.0, 80.0, and 100.0 cm.
Why Time Several Oscillations?
Timing one oscillation may take only a short time.
Human reaction time can then represent a significant fraction of the measurement.
Instead of timing:
1 oscillation
we might time:
10 oscillations
and divide by 10.
This reduces the relative effect of reaction-time uncertainty.
Good methods are designed to improve the quality of the measurements.
Worked Example: Reaction Rate
Research question:
How does acid concentration affect reaction time?
A method might specify:
- exact concentration values
- exact volume of acid
- exact mass of reactant
- reaction vessel
- temperature
- endpoint
- timing procedure
- repeated trials
Without these details, differences between trials might result from factors other than acid concentration.
Sequence Matters
Consider:
Start the stopwatch.
Add the reactant.
This is different from:
Add the reactant.
Wait 10 seconds.
Start the stopwatch.
The order of operations can directly affect experimental results.
A scientific procedure must therefore be arranged chronologically.
Timing Events Precisely
Weak:
Time the reaction.
Better:
Start the stopwatch immediately when the magnesium ribbon is added to the acid.
Even better:
Start the stopwatch immediately when the magnesium ribbon makes contact with the acid and stop it when no visible magnesium remains.
The start and endpoint are now defined.
Avoid Ambiguous Words
Avoid words such as:
- some
- a little
- a lot
- quickly
- slowly
- carefully
- warm
- cold
- big
- small
unless they are clearly defined.
For example:
Instead of:
Add a little water.
write:
Add 10.0 mL of water.
Instead of:
Use warm water.
write:
Use water at 40°C.
"Carefully" Is Not a Measurement
Consider:
Carefully pour the acid into the beaker.
The word "carefully" may be appropriate as general guidance, but it does not describe the experimental quantity.
A better instruction might be:
Measure 25.0 mL of dilute hydrochloric acid using a measuring cylinder and slowly transfer it into the beaker while wearing eye protection.
This provides both procedural and safety information.
Controlling Human Technique
Some experiments depend heavily on what a person does.
Examples include:
- stirring
- releasing an object
- timing
- shaking
- counting
- judging colour
- measuring from a ruler
These actions should be standardized where possible.
For example:
Release the ball without applying an additional push.
is better than:
Drop the ball.
Using Technology to Improve Repeatability
Technology can sometimes make methods more consistent.
Examples include:
- light gates for timing
- motion sensors
- temperature probes
- electronic balances
- data loggers
- video analysis
- digital pH probes
These tools may reduce some forms of human measurement error.
However, they must still be used correctly and calibrated where appropriate.
Reproducibility Does Not Mean Identical Results
Even when two researchers follow the same method, their measurements may not be exactly identical.
For example:
Researcher A:
12.4 s
Researcher B:
12.7 s
Researcher C:
12.5 s
Small differences can occur because all measurements contain some uncertainty.
Replication helps determine whether the overall result or pattern is consistent.
Repeatability and Reliability
A method that produces similar results when repeated under the same conditions provides evidence of good repeatability.
For example:
Trial 1: 25.2 cm
Trial 2: 25.1 cm
Trial 3: 25.3 cm
These measurements are very consistent.
This does not automatically prove they are accurate, but it suggests good repeatability.
Repeatable Does Not Always Mean Accurate
Suppose a balance has a calibration error and always reads:
2.0 g too high
Repeated measurements may be extremely similar.
For example:
12.0 g
12.0 g
12.1 g
The measurements are repeatable but may not be accurate.
Repeatability is important, but it is not the only measure of experimental quality.
Random Variation
Repeated measurements may differ because of random variation.
For example:
15.2 s
14.9 s
15.4 s
Repeating trials and calculating a mean can reduce the influence of random variation.
However, repetition does not automatically correct a systematic problem with the method or equipment.
Method vs Results
The method describes what you did.
The results describe what happened.
Method:
Measure the temperature every 30 seconds for 5 minutes.
Results:
The temperature decreased from 82°C to 54°C over 5 minutes.
Do not mix results into the method.
Method vs Explanation
The method usually focuses on what was done.
Scientific reasoning explaining why the results occurred generally belongs in the analysis or discussion.
For example:
Method:
Place the beaker in a 50°C water bath for five minutes.
Analysis:
The increased temperature gave the particles greater average kinetic energy.
Keeping sections distinct makes the report easier to follow.
Worked Example: Improving a Weak Method
Weak instruction:
Heat the water and measure it.
Problems:
- no volume
- no target temperature
- no equipment
- unclear measurement
- unclear timing
Improved:
Measure 100 mL of water using a measuring cylinder, transfer it to a 250 mL beaker, and heat it until a thermometer reads 50°C.
The instruction can now be reproduced much more accurately.
Another Method Improvement
Weak:
Drop the ball and measure the bounce.
Improved:
Hold the bottom of the ball at a height of 1.00 m above the floor. Release the ball without applying a downward force. Record the maximum height reached during the first rebound using a vertically positioned metre ruler.
The improved version defines both the starting condition and measurement.
Error Analysis
A student writes:
1. Add water to a beaker.
2. Add 10 g of salt.
3. Record how long it takes to dissolve.
What information is missing?
Possible missing details include:
- volume of water
- water temperature
- type of salt
- stirring procedure
- equipment used for timing
- definition of "dissolved"
- number of repeated trials
The procedure cannot yet be replicated reliably.
Another Error Analysis
A student writes:
Repeat the experiment several times.
What does "several" mean?
A stronger instruction is:
Repeat the experiment three times at each value of the independent variable and calculate the mean.
Specific instructions improve repeatability.
Another Error Analysis
A student writes:
Heat the solution until it is very hot.
"Very hot" is subjective.
One student might interpret this as:
50°C
another as:
80°C
A stronger instruction is:
Heat the solution until it reaches 70°C, as measured using a thermometer.
A Reliable Method-Writing Strategy
Before writing the method, answer these questions:
1. What am I changing?
Identify the independent variable.
2. What values will I test?
Specify the range and intervals.
3. What am I measuring?
Identify the dependent variable.
4. Exactly how will I measure it?
Specify equipment, units, and endpoint.
5. What must remain constant?
Identify important controlled variables.
6. How will I keep them constant?
Describe the control procedure.
7. How many trials will I perform?
Plan repetition.
8. What are the hazards?
Identify appropriate safety precautions.
9. How will I record the data?
Prepare tables or recording systems.
10. Could another person follow these instructions without asking me questions?
If not, more detail is needed.
Method-Writing Checklist
Before submitting a scientific method, check:
- Are the steps numbered?
- Are they in chronological order?
- Does each step use a clear action verb?
- Are quantities specified?
- Are units included?
- Is the equipment identified where necessary?
- Is the independent variable clearly changed?
- Are the values of the independent variable stated?
- Is the dependent variable clearly measured?
- Is the measurement method defined?
- Are important controlled variables addressed?
- Are repeated trials included?
- Is data recording explained?
- Are relevant hazards identified?
- Are suitable safety precautions included?
- Could another student reproduce the investigation?
Did You Know?
Some of the most important details in a scientific paper are found in its methods.
A surprising result is much more convincing when other researchers can independently perform a similar investigation and obtain compatible evidence.
This is one reason scientists describe their experimental procedures carefully.
Science depends not only on obtaining results but also on being able to examine how those results were obtained.
Key Terms
- Method: Step-by-step description of how an investigation is performed.
- Procedure: Another term for the experimental method.
- Replication: Independent repetition of an investigation using the same or closely matched method.
- Repetition: Repeating measurements or trials under the same conditions.
- Repeatability: Degree to which repeated measurements under the same conditions produce similar results.
- Independent variable: Variable deliberately changed.
- Dependent variable: Variable measured or observed.
- Controlled variable: Factor kept as constant as reasonably possible.
- Operational definition: Precise description of how a variable or condition will be measured or identified.
- Trial: One complete performance of an experimental condition.
- Hazard: Something with the potential to cause harm.
- Risk: Likelihood and consequence of harm occurring.
- Precaution: Action taken to reduce risk.
- Random variation: Unpredictable differences between repeated measurements.
- Systematic error: Consistent bias affecting measurements.
- Reliability: Consistency of evidence or measurements.
- Accuracy: Closeness of a measurement to the accepted or true value.
Key Relationships
A strong method connects:
Research question → Variables → Procedure → Measurements → Results
A repeatable method clearly identifies:
what changes + what is measured + what stays controlled
A useful safety statement connects:
Hazard → Risk → Precaution
Repeated measurements allow:
Trials → Comparison → Mean → Better assessment of consistency
A strong procedure follows:
Prepare → Measure → Change → Observe → Record → Repeat
Key Takeaways
- A scientific method explains exactly how an investigation is performed.
- The method should be detailed enough for another person to reproduce the investigation.
- Good methods are clear, specific, measurable, logical, and safe.
- Procedures should normally be presented in chronological order.
- Numbered steps make methods easier to follow.
- Clear action verbs improve scientific communication.
- Quantities should be specified rather than described vaguely.
- Measurements should include appropriate units.
- Relevant equipment should be identified.
- The independent variable and its tested values should be clearly described.
- The method must explain exactly how the dependent variable is measured.
- Operational definitions make measurements and observations more consistent.
- Important controlled variables should be identified and controlled through specific procedures.
- Repeated trials help scientists assess consistency and identify unusual results.
- Repetition and replication are related but different concepts.
- Repetition occurs within an investigation, while replication involves independently repeating an investigation.
- Safety should be integrated into experimental design.
- Useful safety precautions identify a specific hazard and explain how risk will be reduced.
- Diagrams can support complicated experimental setups but should not replace a clear written procedure.
- Ambiguous words such as "some," "a little," "warm," or "quickly" should be replaced with measurable instructions whenever possible.
- Start and endpoint conditions should be clearly defined when timing experiments.
- Human techniques such as stirring, releasing, and judging endpoints should be standardized where possible.
- Appropriate technology can improve the consistency and precision of measurements.
- Repeatable results are not necessarily accurate results.
- Repetition can reduce the influence of random variation but does not automatically remove systematic error.
- The method should describe what was done, while results describe what happened.
- Scientific explanations of the results generally belong in the analysis rather than the method.
- A useful final test is to ask whether another researcher could perform the investigation without needing additional instructions.