In the reaction between marble chips and hydrochloric acid, the rate can be followed by measuring
- A. the mass of the flask, which falls as carbon dioxide escapes
- B. the colour of the acid
- C. the temperature of the marble
- D. the mass of the flask, which rises as gas is produced
Explanation
Carbon dioxide leaves the open flask, so the total mass decreases steadily and the loss per unit time is a direct measure of the rate. The alternative method is to collect the gas in a syringe and record its volume at fixed intervals. Mass could never increase, since nothing is entering the flask from outside.