1. In a chemical reaction
combine in different ways to form new
.
2. Whatever the change, you cannot
any atoms. This is known as the law of
of
. It means that if you could weigh the
at the start, and then compare this with the
of all the
formed at the end, they would be
.
3. Two sorts of situation can appear at first sight to contradict this law.
3a. When a metal is heated in air it
mass in forming the metal oxide.
3b. When a carbonate dissolves in acid, the mixture
mass.
3c. Both these situations involve the 'adding' or losing' of a
, which is rather difficult to
!
4. From the 'law' in 2. you can make
about the quantities of chemicals involved in a reaction.
4a. For example, 24g of magnesium burns in air and combines with 16g of oxygen to form 40g of magnesium
, even if you can't weigh the oxygen!
4b. This means 36g of magnesium will combine with 24g of oxygen from the air to form
g of magnesium oxide.
4c. If
g of magnesium is burned it combines with 4g of oxygen to form 10g of magnesium oxide.
4d. Burning 12g of magnesium will combine with
g of oxygen to make
g of magnesium oxide
4e. burning
g of magnesium will combine with
g of oxygen to make 80g of magnesium oxide.