Practical activity - measuring rates of reaction by production of gas
There are a number of ways that you could investigate the effect of changing the conditions on the rate of a reaction in Chemistry. This is an outline of the required steps to undertake one of these methods.
It is important in this practical to use appropriate apparatus to make and record a range of measurements accurately, including mass, time, temperature and volume. This includes using apparatus safely and monitoring chemical changes.
Aims
To investigate the effect of changing the conditions 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.
Part 1 Changing the concentration of acid
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.
- Record the time for every 10 cm3 of gas produced.
- When the reaction is complete, clean the apparatus as directed by your teacher.
- Repeat steps 1 to 5 with different concentrations of hydrochloric acid.
Results
Record the results in a table using (s) for time and (cm3) for volume.
| Time | Volume |
| 0 | 0 |
| 10 | |
| 20 |
| Time | 0 |
|---|---|
| Volume | 0 |
| Time | |
|---|---|
| Volume | 10 |
| Time | |
|---|---|
| Volume | 20 |
Analysis
- 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
- For each concentration of acid, calculate the mean rate of reaction:
- mean rate of reaction (g/cm3) = \(\frac{total~mass~of~gas~produced~(cm^3)}{reaction~time~(s)}\)
- 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.
Part 2 Changing the temperature
Carry out the experiment described above, but:
- keep the concentration of acid the same
- warm the acid to different temperatures using a hot water bath or a Bunsen burner, tripod and gauze
- measure and record the temperature of the acid
- describe the effect of increasing the temperature on the mean rate of reaction
Part 3 Changing the surface area to volume ratio
Carry out the experiment described above, but:
- keep the temperature and concentration of acid the same
- use different sized pieces of calcium carbonate, including a powder
- describe the effect of increasing the surface area to volume ratio (decreasing the particle size) on the mean rate of reaction
Hazards, risks and precautions
It is important in this practical activity to use appropriate apparatus and methods. This includes the safe use and careful handling of substances.
Evaluate the hazards and the precautions needed to reduce the risk of harm. For example:
| Hazard | Possible harm | Possible precaution |
| Hot hydrochloric acid | Skin and eye irritation; burns to the skin | Wear gloves and eye protection; do not heat above 60°C |
| Fizzing in the reaction mixture | 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 | Hot hydrochloric acid |
|---|---|
| Possible harm | Skin and eye irritation; burns to the skin |
| Possible precaution | Wear gloves and eye protection; do not heat above 60°C |
| Hazard | Fizzing in the reaction mixture |
|---|---|
| Possible harm | 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 |