Chemguide: Core Chemistry 14 - 16

Answers to Set 1 of the equations problems

You need to balance:

Mg + HCl     MgCl₂ + H₂

Balanced version:

Mg + 2HCl     MgCl₂ + H₂

You need to balance:

Ba + H₂O     Ba(OH)₂ + H₂

Balanced version:

Ba + 2H₂O     Ba(OH)₂ + H₂

You need to balance:

FeSO₄ + NaOH     Fe(OH)₂ + Na₂SO₄

Balanced version:

FeSO₄ + 2NaOH     Fe(OH)₂ + Na₂SO₄

In examples like this, where groups of atoms are unchanged from one side of the equation to the other, you can save yourself a bit of time by counting up the groups rather than all the individual atoms. So, for example, you originally have 2 OH groups on the right but only one on the left. You have 1 sulfate group on the left, and still have 1 sulfate group unchanged on the right.

You need to balance:

Al + Fe₂O₃     Al₂O₃ + Fe

Balanced version:

2Al + Fe₂O₃     Al₂O₃ + 2Fe

You need to balance:

Na₂CO₃ + HNO₃     NaNO₃ + CO₂ + H₂O

Balanced version:

Na₂CO₃ + 2HNO₃     2NaNO₃ + CO₂ + H₂O

In this case you could, if you wanted to, count the nitrate group as a whole because it is unchanged. The carbonate group, of course, is changed and so you have to count up its atoms separately. If you find this confusing, ignore it and just count everything up.

You will probably find that with experience, you will tend to spot groups which are unchanged and treat them as a single unit rather than a lot of individual atoms.

Return to the problems . . .