Emperical Formula

1) Complete this:

a) - Empirical formula: CH

- Mr:78

- Molecular Formula: ???

b) – Emperical Formula: ???

- Mr: 180

Molecular Formula: C^6H^12O^6

2) Calculate the empirical formula of the following substances.

a) Ca 20%Br 80%

b) Pb 90.7%O9.3%

3) 2.4g of magnesium was burnt in excess of chlorine gass. The mass increase due to chlorine being found to be 7.1g. Calculate the molecular formula og magnesium chloride.

4) A 1.50 g sample of hydrocarbon undergoes complete combustion to produce 4.40 g of CO2 and 2.70 g of H2O. What is the empirical formula of this compound? In addition, its molecular weight has been determined to be about 78. What is the molecular formula?

Mark Schme

1)a) C^6H^6

b) CH^2O

2)a) CaBr^2

b)PbO^2

3) MgCl^2

4)CH^2O