Atoms, ions, formulae and relative massesEdexcel International A Level Chemistry: Mind map

Exam questions on Atoms, ions, formulae and relative masses

1. A garden-centre chemist checks the label on a fertiliser that contains ammonium sulfate, (NH₄)₂SO₄. Relative atomic masses: H = 1.0, N = 14.0, O = 16.0, S = 32.1.
   Calculate the percentage by mass of nitrogen in ammonium sulfate. Give your answer to 3 significant figures.2 marks
2. Chemists measure relative atomic masses on the carbon-12 scale. A data book gives the relative atomic mass of magnesium as 24.3, although naturally occurring magnesium contains only atoms with mass numbers 24, 25 and 26.
   Explain why the relative atomic mass of magnesium has no units, whereas the molar mass of magnesium is 24.3 g mol⁻¹.2 marks
3. A school air-quality sensor reports the carbon dioxide concentration in a sealed classroom of volume 180 m³ as 1250 ppm by volume. Dry air contains 0.93% argon by volume. 1 m³ = 1000 dm³.
   Calculate the volume, in dm³, of carbon dioxide in the classroom.3 marks