Measuring the rate where a gas is produced
The apparatus needed depends on the nature of the product being measured.
Mass
The mass of a substance 鈥 solid, liquid or gas 鈥 is measured with a balance. This mass balance could be attached to a data logger to measure the decrease in mass against time continuously and produce a graph instantly. The data logger does not make the mass balance any more accurate. Cotton wool is used in the neck of the flask as it allows the gas to escape.
Volume
The volume of a gas is usually measured with a gas syringe (or sometimes with an upside-down measuring cylinder) when the chemical reaction produces a gas, eg metal reacting with acid to produce hydrogen.
Advantages for gas syringe/disadvantages for gas jar:
- gas syringe has a precise scale, gas jar does not
- tube beneath the trough may slip away from under the gas jar
Advantages for gas jar/disadvantages for syringe:
- no time delay in connecting the syringe
- all the gas produced is from the reaction mixture