Core practical

Investigate the rate of a reaction by measuring the production of a gas

There are a number of ways to investigate 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 core practical to use appropriate apparatus to make and record a range of measurements accurately, including mass, time, temperature and volume.

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.

Changing the concentration of acid

Method

A sealed conical flask connected to a gas syringe. The flask contains a reaction mixture that is giving off bubbles of gas.
  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 the teacher.
  6. Repeat steps 1 to 5 with different concentrations of hydrochloric acid.

Results

Record the results in a table.

Time (s)Volume
00 cm3
10 cm3
20 cm3

Analysis

  1. For each concentration of hydrochloric acid, plot a graph on the same set of axes to show:
    • volume of gas (cm3) on the vertical axis
    • time (s) on the horizontal axis
    • a curve of best fit
  2. For each concentration of acid, plot a graph to show: mean~rate~of~reaction~(cm^{3}/s = \frac{total~volume~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 it is possible to tell that the reaction is complete.

No more gas is produced and the line on the graph becomes horizontal.

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

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:

HazardHarmPrecaution
Hot hydrochloric acidCauses skin and eye irritation and burns to the skin Wear gloves and eye protection and 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 and do not look over the top when adding the calcium carbonate