Relative Formula Mass expressed in grams

• The relative formula mass of a molecule or compound can be expressed in grams.

• The relative formula mass measured in grams is called one mole of the substance.

Calculate relative formula masses andexpress them in grams

HCl

CO2

HNO3

Na2CO3

36.5 g

44 g

63 g

106 g

Hydrogen Chloride

Carbon Dioxide

Nitric Acid

Sodium Carbonate

The relative formula mass of all gases expressed in grams has a certain volume

Volume = 22.4 dm3 at 0oC

1 dm3 (=1 litre) is about thesize of a very big glass of water

Volume = 24 dm3 at 20oC

Here are examples

Mass Volume

2 g H2 gas =

44 g CO2 gas =

16 g O2 gas =

34 g NH3 gas =

24 dm3 (22.4 dm3)

24 dm3 (22.4 dm3)

12 dm3 (11.2 dm3)

48 dm3 (44.8 dm3)

Calculating masses when given volumes(use 24 dm3)

Volume Mass

3 dm3 Oxygen gas =

6 dm3 Nitrogen gas =

48 dm3 Chlorine gas =

36 dm3 Carbon Dioxide =

4 g

7 g

142 g

66 g

Using balanced equations

The big numbers in front of the reactants and products in balanced chemical equations show the reacting ratios.

H2 + O2 = H2O22

2(1x2)g H2 + 1(2x16)g O2 = 2(1x2+16)g H2O

4g H2 + 32g O2 = 36g H2O

48 dm3 H2 + 24 dm3 O2 = 48 dm3 H2O

Calculate the ratio of atoms in compounds from supplied masses or % composition

(empirical formulae)

Sodium Oxide

Sodium 46g Oxygen 16g

Sodium 23 46/23 = 2

Oxygen 16 16/16 = 1

Formula for Sodium Oxide Na2O