AQA GCSE Combined Science: Chemistry: Quantitative Chemistry

A student heated a sample of copper in an open crucible. The copper reacted with oxygen from the air to form copper oxide, and the student found that the mass increased.

In a different experiment, a student heated green copper carbonate in an open crucible. It decomposed to form copper oxide and carbon dioxide, and this time the mass decreased.

Explain, using the idea of conservation of mass, why the mass increased in the first experiment but decreased in the second. (6 marks)

Magnesium burns in oxygen to form magnesium oxide:

2Mg(s) + O₂(g) → 2MgO(s)

A student burned 4.8 g of magnesium completely.

(Relative atomic masses: Mg = 24; O = 16.)

(a) Calculate the number of moles of magnesium in 4.8 g. (2 marks)

(b) Calculate the maximum mass of magnesium oxide that could be produced. Show your working. (2 marks)

Ammonium nitrate has the formula NH₄NO₃. It is used as a fertiliser because it contains a high percentage of nitrogen.

(Relative atomic masses: H = 1; N = 14; O = 16.)

(a) Calculate the relative formula mass (Mr) of ammonium nitrate, NH₄NO₃. (1 mark)

(b) Calculate the percentage by mass of nitrogen in ammonium nitrate. Give your answer to 1 decimal place. (2 marks)

A student dissolved 20 g of sodium hydroxide (NaOH) in water and made the solution up to a total volume of 500 cm³.

(a) Calculate the concentration of the solution in g/dm³. Show your working. (2 marks)

(b) State what happens to the concentration of this solution, in g/dm³, if more water is added without adding any more sodium hydroxide. (1 mark)

Hydrogen reacts with nitrogen to make ammonia:

N₂(g) + 3H₂(g) → 2NH₃(g)

A reaction mixture contains 1 mol of nitrogen (N₂) and 2 mol of hydrogen (H₂).

Identify the limiting reactant and explain your answer. (2 marks)

In a closed flask, a chemical reaction takes place between two solutions. No gas is allowed to escape.

State what happens to the total mass inside the closed flask during the reaction. (1 mark)