Gases are usually expressed in terms of volume, but to compare volumes measured under different conditions, they must be converted to normal temperature and pressure using gas laws. The volume of a gas can also be converted to its weight and vice versa using the relation that the mass of a gas is directly proportional to its density and volume. For example, 2 grams of sulfur burned to form SO2 can be used to calculate the volume of oxygen consumed at standard temperature and pressure.

8. • Gases are usually expressed in terms of volumes.
• In case the volume of the gas is measured at room temperature and
pressure (or any condition other than NTP), convert it into NTP by
applying gas laws.
• Volume of a gas at any temperature and pressure can be converted
into its weight and vice-versa with the help of the relation,

10. • Illustration 11: Two grams of sulphur is
completely burnt in oxygen to form SO2
• What is the volume (in L) of oxygen consumed
at STP?

14. and

16. Class work
• Calculate how many CO2 molecules there are
in 8,8 g gas.
• Calculate what volume of a 0,3 mol.dm−3
oxylic acid solution contains 22,5 g oxylic acid
((COOH)2).