Experiment - Determination of molar volume for a gas

Introduction

When magnesium metal reacts with a dilute mineral acid, such as sulphuric acid, it produces hydrogen gas and an aqueous solution of magnesium sulphate, according to the following equation,

Mg(s) + H2SO4(aq) MgSO4(aq) + H2(g)

If the volume of hydrogen gas produced is measured then the molar volume, i.e. volume that one mole occupies, of a gas may be calculated.

Method

Take one of the small pieces of magnesium ribbon and weigh it, noting down its mass. Place the magnesium ribbon into a large beaker of water. Fill a 50 cm3 measuring cylinder full to the brim with dilute sulphuric acid and stopper the end. Now invert the full measuring cylinder into the beaker and quickly remove the stopper from it making sure you cover the ribbon, so as to collect the hydrogen gas evolved.

Either allow the magnesium ribbon to react fully with the sulphuric acid, in which case make a note of the volume of water displaced in the measuring cylinder (which is the volume of hydrogen gas evolved), or if 50 cm3 of gas is evolved then remove the cylinder and quickly measure the new length of magnesium ribbon.

Calculations

(1) From the mass of the piece of magnesium ribbon used calculate the amount of magnesium ribbon used.

(2) From the chemical equation given at the top deduce the amount of hydrogen gas produced.

(3) From the answer to (2) and the noted volume of hydrogen gas produced, calculate the volume one mole of hydrogen would occupy (the molar volume) in dm3 mol-1.