Measuring CO2 from reactions

Experiment how much carbon dioxide can be made from the mixture of solid barium sulphate and potassium carbonate

Introduction

Teachers who have not used the problems before should read the section Using the problems before starting.

Prior knowledge

pH of solutions of ionic compounds, tests for ions and solubility rules. A detailed knowledge is unnecessary as students are encouraged to consult textbooks and data books during the exercise.

Equipment

Data books and inorganic textbooks should be available for reference.

• A mixture of solid barium sulphate and potassium carbonate should be prepared. The mixture could be anywhere from 10 g of barium sulphate to 5 g of potassium carbonate to 5 g of barium sulphate and 10 g of potassium carbonate. Weighing on a two decimal place balance is sufficient; the teacher should keep a note of the masses used.

Students can request apparatus and chemicals during the practical session and these should be issued if they are safe to use. The following are likely to be needed:

• Volumetric glassware;
• standard strong acid and an indicator such as methyl orange;
• a 2-decimal place top-pan balance; and
• filtration equipment.

Possible methods

1. Stir the mixture with water and filter the ensuing suspension. Wash the residue, barium sulphate, with a little more water before drying it to a constant mass in an oven. It is recommended to use a two decimal place top-pan balance.
2. Stir the mixture with water and titrate the solution against standard strong acid.
3. Measure the loss of mass on reacting the mixture with excess strong acid. This is best done in a conical flask with a glass wool plug to prevent any liquid spraying out. A two decimal place top-pan balance is again recommended.
4. Measure the volume of gas evolved when the mixture is reacted with excess strong acid.
5. As number 4, but absorb the gas evolved in an alkali such as aqueous sodium hydroxide or aqueous calcium hydroxide, and measure the increase in mass of the alkali.
6. As for method 1, but add aqueous barium chloride or calcium nitrate to the filtrate to precipitate out the carbonate ions.

With methods 3, 4 and 5 some of the carbon dioxide remains dissolved in the water.

Notes

1. Another insoluble salt (not a carbonate or sulphite) can be used.
2. Information about generating and collecting the gas will probably be needed for methods 4 and 5.