Some of the fertilizers are sodium nitrate NaNO₃, ammonium sulphate (NH₄)₂SO₄ and urea CO(NH₂)₂. Which of these contains the highest percentage of nitrogen?

200 cm³ of CO₂ is collected at STP when a mixture of acetylene and oxygen is ignited. Calculate the volume of acetylene and oxygen at STP in the original mixture.

2C₂H₂ (g) + 5O₂ (g) ⟶ 4CO₂ (g)+ 2H₂O (g)

Find the molecular formula of a hydrocarbon having vapour density 15, which contains 20% of Hydrogen.

The following experiment was performed in order to determine the formula of a hydrocarbon. The hydrocarbon X is purified by fractional distillation.

0.145 g of X was heated with dry copper (II) oxide and 224 cm³ of carbon dioxide was collected at S.T.P.

(a) Which elements does X contain?

(b) What was the purpose of copper (II) oxide?

(c ) Calculate the empirical formula of X by the following steps:

(i) Calculate the number of moles of carbon dioxide gas.

(ii) Calculate the mass of carbon contained in this quantity of carbon dioxide and thus the mass of carbon in sample X.

(iii) Calculate the mass of hydrogen in sample X.

(iv) Deduce the ratio of atoms of each element in X (empirical formula).