In this practice IB calculate the relative molecular mass of carbon dioxide, CO2, by application of the ideal gas equation.

The ideal gas equation can be used to calculate the molar mass (M) of a gas when P, V, T, and the mass of the gas sample (m) are known:

PV=nRT

Given that , n=g/ MM  this rearranges to MM=gRT/PV

In this experiment we will heat a known mass of copper carbonate in a test tube. The solid will undergo thermal decomposition, releasing carbon dioxide and leaving copper oxide:

CuCO₃(s) → CuO(s) + CO₂(g)

The carbon dioxide gas given off will be collected by displacement of water from an inverted glass tube.

After heating, the test tube and contents are reweighed.

We can determine the molar mass of carbon dioxide from the following data collected in this experiment:

• mass (m) of gas: calculated from the loss in mass on heating the copper carbonate
• volume (V) of gas: measured from the volume of water displaced
• temperature (T) of gas: the measured room temperature
• pressure (P): the measured room pressure