4. reacting masses and chemical equations

Question 1

finding formulae of compounds

Answer 1

1. from the structure of compound
2. valency
   3.balancing charges

Question 2

relative molecular mass (Mr)

Answer 2

addition of Ar values

Question 3

laws of chemistry

Answer 3

1. elements always react in the same ratio to form a given compound
2. total mass doesnt change during a chemical reaction

Question 4

% composition of a compound

Answer 4

1. write down formula
2. using Ar values, work out its Mr
   3write the mass of the element as a fraction of its Mr
3. multiple fraction by 100

Question 5

% purity

Answer 5

( mass of pure substance in it / total mass ) x 100