Required practical

Measuring 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

  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. Every 10 seconds, record the volume of gas produced.
  5. When the reaction is complete, clean the apparatus as directed by a 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.Measuring the volume of carbon dioxide using a gas syringe.

Results

Record the results in a table.

Time (s)Volume (cm3)
00
1050
20100

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:

HazardPossible harmPossible precaution
Hydrochloric acidCauses skin and eye irritationWear eye protection
Fizzing in the reaction mixtureAcidic spray 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