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

  1. Support a gas syringe with a stand, boss and clamp.
  2. Using a measuring cylinder, add 50 cm3 of dilute hydrochloric acid to a conical flask.
  3. Add 0.4 g of calcium carbonate to the flask. Immediately connect the gas syringe and start a stop clock.
  4. Record the time for every 10 cm3 of gas produced.
  5. When the reaction is complete, clean the apparatus as directed by your teacher.
  6. Repeat steps 1 to 5 with different concentrations of hydrochloric acid.
A sealed conical flask connected to a gas syringe. The flask contains a reaction mixture that is giving off bubbles of gas.

Results

Record the results in a table using (s) for time and (cm3) for volume.

TimeVolume
00
10
20

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:
    • mean rate of reaction (g/cm3) = \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.

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:

HazardPossible harmPossible precaution
Hot hydrochloric acidSkin and eye irritation; burns to the skinWear gloves and eye protection; do not heat above 60°C
Fizzing in the reaction mixtureSpray or foam escaping, which may damage skin and eyesUse a large conical flask so there is plenty of space inside; do not look over the top when adding the calcium carbonate