The mole, concentration and empirical formulaeEdexcel International A Level Chemistry: Mind map

Exam questions on The mole, concentration and empirical formulae

1. A technician weighs 5.85 g of sodium chloride, NaCl (molar mass 58.5 g mol⁻¹), dissolves it in water and makes the solution up to 250 cm³. The Avogadro constant, L, is 6.02 × 10²³ mol⁻¹.
   Calculate the concentration of the solution in mol dm⁻³ and in g dm⁻³.2 marks
2. A laboratory stock bottle holds 500 cm³ of sulfuric acid of concentration 0.250 mol dm⁻³. The molar mass of sulfuric acid, H₂SO₄, is 98.1 g mol⁻¹.
   Calculate the mass of sulfuric acid needed to make 2.50 dm³ of solution of the same concentration.2 marks
3. A student analyses two compounds. Compound P, an oxide of iron, contains 2.10 g of iron and 0.90 g of oxygen. Compound Q is a hydrocarbon with relative molecular mass 70.0 that contains 85.7% carbon by mass. Relative atomic masses: H = 1.0, C = 12.0, O = 16.0, Fe = 55.8.
   Use the data to calculate the empirical formula of compound P.3 marks