Required practical - measure the production of a gas
It is important in this core practical to use appropriate apparatus to make and record a range of measurements accurately, including mass, time, temperature and volume. This includes the safe use of apparatus, and monitoring chemical changes.
This outlines one way to carry out the practical. Eye protection must be worn.
Aims
To investigate the effect of changing the concentration on the rate of a reaction.
Calcium carbonate reacts with dilute hydrochloric acid:
calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide
CaCO3(s) + 2HCl(aq) → CaCl2(aq) + H2O(l) + CO2(g)
The volume of carbon dioxide gas produced can be measured using a gas syringe.
Method
- Support a gas syringe with a stand, boss and clamp.
- Using a measuring cylinder, add 50 cm3 of dilute hydrochloric acid to a conical flask.
- Add 0.4 g of calcium carbonate to the flask. Immediately connect the gas syringe and start a stop clock.
- Every 10 seconds, record the volume of gas produced.
- When the reaction is complete, clean the apparatus as directed by a teacher.
- Repeat steps 1 to 5 with different concentrations of hydrochloric acid.
Results
Record the results in a table.
| Time (s) | Volume (cm3) |
| 0 | 0 |
| 10 | /p |
| 20 | /p |
| Time (s) | 0 |
|---|---|
| Volume (cm3) | 0 |
| Time (s) | 10 |
|---|---|
| Volume (cm3) | /p |
| Time (s) | 20 |
|---|---|
| Volume (cm3) | /p |
Analysis
1. For each concentration of hydrochloric acid, plot a graph to show:
- volume of gas (cm3) on the vertical axis
- time (s) on the horizontal axis
- draw a curve of best fit
2. For each concentration of acid, calculate the mean rate of reaction until the reaction stops:
\(mean~rate~of~reaction~(cm^{3}/s) = \frac{total~mass~of~gas~produced~(cm^{3})}{reaction~time~(s)}\)
3. Describe the effect of increasing the concentration of acid on the mean rate of reaction. Use your graphs and calculations in step 2 to help you.
Evaluation
Question
Describe how you can tell that the reaction is complete.
No more gas is produced, and the line on the graph becomes horizontal.
Hazards, risks and precautions
Evaluate the hazards and the precautions needed to reduce the risk of harm.
For example:
| Hazard | Possible harm | Possible precaution |
| Hydrochloric acid | Causes skin and eye irritation | Wear eye protection |
| Fizzing in the reaction mixture | Acidic spray or foam escaping, which may damage skin and eyes | Use a large conical flask so there is plenty of space inside; do not look over the top when adding the calcium carbonate |
| Hazard | Hydrochloric acid |
|---|---|
| Possible harm | Causes skin and eye irritation |
| Possible precaution | Wear eye protection |
| Hazard | Fizzing in the reaction mixture |
|---|---|
| Possible harm | Acidic spray or foam escaping, which may damage skin and eyes |
| Possible precaution | Use a large conical flask so there is plenty of space inside; do not look over the top when adding the calcium carbonate |