Rate Equations

Question 1

When investigating the rate of reaction between calcium carbonate and hydrochloric acid, suggest why a loose cotton wool plug is placed in the neck of the flask, instead of leaving the flask open or inserting a bund.

Answer 1

Instead of leaving the flask open: to avoid splashing
Instead of inserting a bung: to allow gas/CO2 to escape

Question 2

When investigating their rate of reaction, suggest why using a large excess of calcium carbonate means that the rate is only affected by the changing concentration of hydrochloric acid.

Answer 2

so that the surface area/mass/amount stays approximately constant

Question 3

In an experiment the variable measured is mass loss. The rate of this reaction at a constant temperature can be investigated in other ways. Suggest two other variables that can be measured instead of mass loss.

Answer 3

• volume of gas produced
• pH
• concentration of reactant