1. Start here
You will plan a fair test, run a simulated experiment, record your own readings and use your evidence to explain what you find.
How does the concentration of hydrochloric acid affect the rate of its reaction with magnesium?
By the end of this lab, I can
- identify what to change, what to measure and what to keep the same in a rate investigation, and choose suitable apparatus;
- show by calculation that the acid is in excess and work out the maximum volume of hydrogen;
- read a gas syringe and record results in a table with correct headings and units;
- describe what I observe without mixing in explanations;
- use a volume–time graph to compare rates and explain why the final volume is the same;
- explain, using collisions between particles, why more concentrated acid reacts faster;
- judge a claim and a method using evidence.
Suggested timing (50 minutes)
| Predict | 3 min | Plan and calculate | 8 min |
| Procedure | 3 min | Experiment and results | 14 min |
| Observations | 4 min | Graph and processing | 6 min |
| Discussion | 7 min | Feedback, retry and submit | 5 min |
How this lab works
Each step asks you to decide, check and improve. Use Check to get feedback, and Hint if you are stuck. The third hint shows worked reasoning, and it unlocks after you have tried once.
The experiment uses a simplified model. Its numbers are simulated, and time can be sped up. Safety notes and keyboard help are under Help and safety at the top.
2. Predict
Decide what you think will happen before you see any results. Predictions are not marked. You will compare yours with your evidence later.
3. Plan
Make the planning decisions a scientist would make. Check each answer and act on the feedback.
A. Variables
B. Apparatus
C. Will the acid be in excess in every run?
You will use 0.060 g of magnesium ribbon and 50.0 cm3 of acid in every run. The weakest acid is 0.50 mol/dm3. Ar of Mg = 24. One mole of any gas occupies 24 dm3 at room temperature and pressure.
4. Procedure and apparatus
Read the method, then answer two questions about why it is done this way.
Apparatus
Method
- Use a 50 cm3 measuring cylinder to pour 50.0 cm3 of hydrochloric acid of the chosen concentration into a conical flask.
- Clean a strip of magnesium ribbon with sandpaper. Weigh out 0.060 g on an electronic balance.
- Check that the gas syringe plunger is pushed fully in (0 cm3) and moves freely. Connect it to the delivery tube.
- Drop the magnesium into the acid, fit the bung immediately and start the stopwatch.
- Read the gas syringe every 20 s up to 120 s. Then wait until the volume stops changing and record the final volume.
- Rinse the flask. Repeat with each concentration, using fresh acid and a fresh 0.060 g of magnesium each time, at the same temperature.
Why is it done this way?
5. Run the experiment and record your results
Choose a concentration and start the run. Read the gas syringe at each reading time and type the volume into the table. Complete at least three concentrations; all four gives a clearer pattern.
Save your prediction in Step 2 before you run the experiment.
Reading window: magnified syringe scale
Read the scale at the inner edge of the plunger (the solid band at its end). Each small mark is 1 cm3.
Simulated data from a simplified model. Above 1× speed, time is accelerated; the clock always shows simulated seconds.
Results table
Choose a heading for each column. Then type each reading to the nearest 1 cm3. The 0 s row is filled in for you.
6. Observations
An observation is what you can see or measure. Describe first; explain later.
A. Describe what you observed
B. Observation, identification or explanation?
7. Process and interpret your data
Calculated values are kept separate from your raw readings. The graph is drawn from the readings you typed.
A. Average rate over the first 20 s
Average rate = volume of hydrogen at 20 s ÷ 20 s. Give each answer to 2 significant figures.
B. Volume–time graph of your results
These lines join your points. On graph paper you would draw a smooth best-fit curve. The data are simulated, so use them to describe the trend, not to state an exact mathematical law.
C. Interpret the graph
8. Discussion
The questions move from recalling facts to judging claims. The label beside each question shows the kind of thinking it needs.
9. My feedback
Your feedback is built from your own choices, readings and answers. First attempts, help from hints or revision, and your independent retry are reported separately.
Keep or hand in your record
Your teacher can review your written answers from this record. It contains no name; write your name on it if your teacher asks.
Copy your written answers into SLS
If your teacher has set these questions in SLS, copy each answer into the SLS question with the same code (W1 to W6).
10. Independent retry
New questions, no hints, one attempt each. This checks whether you can now apply what you learned on your own. Work on your feedback first.
Generate your feedback in Step 9 first.
11. Submit your work
Download a PDF of all your answers, then upload it to your class Google Drive folder.
A. Check what you have done
Send your results to SLS
B. Download your PDF
Your name is kept only in this browser and in the PDF you download.