1. 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.

2. Calculate relative formula masses and express them in grams
Hydrogen Chloride
HCl
36.5 g
Carbon Dioxide
CO2
44 g
63 g
Nitric Acid
HNO3
Sodium Carbonate
Na2CO3
106 g

3. The relative formula mass of all gases expressed in grams has a certain volume
Volume = 22.4 dm3 at 0oC
Volume = 24 dm3 at 20oC
1 dm3 (=1 litre) is about the
size of a very big glass of water

4. Here are examples Mass Volume
2 g H2 gas =
24 dm3 (22.4 dm3)
44 g CO2 gas =
24 dm3 (22.4 dm3)
16 g O2 gas =
12 dm3 (11.2 dm3)
34 g NH3 gas =
48 dm3 (44.8 dm3)

5. Calculating masses when given volumes (use 24 dm3) Volume Mass
3 dm3 Oxygen gas =
4 g
7 g
6 dm3 Nitrogen gas =
142 g
48 dm3 Chlorine gas =
66 g
36 dm3 Carbon Dioxide =

6. Using balanced equations
The big numbers in front of the reactants and products in balanced chemical equations show the reacting ratios.
H2 + O2 = H2O 2 2
2(1x2)g H2 +
1(2x16)g O2 =
2(1x2+16)g H2O
4g H2 + 32g O2 = 36g H2O
48 dm3 H dm3 O2 = 48 dm3 H2O

7. 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