Sec 3 Chemistry Mole Concept & Stoichiometry topical questions

Calculate the relative formula mass of each compound (Na = 23, O = 16, H = 1, S = 32, K = 39, Mn = 55).

1. (a)Na₂O[1]
2. (b)H₂SO₄[1]
3. (c)KMnO₄[1]

Calculate the number of moles in each sample (Mg = 24, CO₂ = 44).

1. (a)6.0 g of magnesium[1]
2. (b)11 g of carbon dioxide[1]

State the volume at r.t.p. of 3.0 mol of nitrogen gas.

Ammonia is made by the reaction N₂ + 3H₂ → 2NH₃. How many moles of ammonia form from 6 mol of hydrogen with excess nitrogen?

9.6 g of magnesium (Ar = 24) burns completely in oxygen: 2Mg + O₂ → 2MgO.

1. (a)Calculate the moles of magnesium burned.[1]
2. (b)Calculate the mass of magnesium oxide formed (MgO = 40).[2]
3. (c)Calculate the moles of oxygen used.[2]

25.0 cm³ of 0.200 mol/dm³ hydrochloric acid reacts exactly with 20.0 cm³ of sodium hydroxide solution: HCl + NaOH → NaCl + H₂O.

1. (a)Calculate the moles of hydrochloric acid used.[2]
2. (b)Work out the concentration, in mol/dm³, of the alkali.[2]
3. (c)State the concentration of the sodium hydroxide in g/dm³ (NaOH = 40).[1]

A sample of an oxide of copper is reduced by hydrogen. 3.2 g of oxide leaves 2.56 g of copper (Cu = 64, O = 16).

1. (a)Calculate the mass and moles of oxygen lost.[2]
2. (b)Calculate the moles of copper formed.[1]
3. (c)Hence find the empirical formula of the oxide.[2]

Excess dilute hydrochloric acid is added to 10.0 g of calcium carbonate (CaCO₃ = 100): CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂.

1. (a)Calculate the moles of calcium carbonate used.[1]
2. (b)Calculate the volume of carbon dioxide at r.t.p. (molar volume 24 dm³).[2]
3. (c)Write the ionic equation for the reaction, with state symbols.[2]

A compound contains, by mass, 40.0% carbon, 6.7% hydrogen and 53.3% oxygen (C = 12, H = 1, O = 16). Its molecular Mr is 180.

1. (a)Calculate the empirical formula.[3]
2. (b)Deduce the molecular formula.[2]

6.4 g of copper(II) oxide (CuO = 80) is warmed with excess dilute sulfuric acid, then the water is evaporated to give pure blue crystals of copper(II) sulfate-5-water (CuSO₄·5H₂O = 250): CuO + H₂SO₄ → CuSO₄ + H₂O.

1. (a)Calculate the moles of copper(II) oxide used.[1]
2. (b)Calculate the maximum mass of copper(II) sulfate-5-water crystals that could form.[3]
3. (c)The student obtains 20.0 g of crystals. Calculate the percentage yield to 3 significant figures.[2]

1.2 g of magnesium (Ar = 24) is added to 50 cm³ of 0.50 mol/dm³ hydrochloric acid: Mg + 2HCl → MgCl₂ + H₂.

1. (a)Calculate the moles of magnesium and of hydrochloric acid.[2]
2. (b)Identify the limiting reagent, with working.[2]
3. (c)Calculate the volume of hydrogen at r.t.p. (molar volume 24 dm³).[2]

A car airbag uses the rapid reaction 2NaN₃ → 2Na + 3N₂ (NaN₃ = 65).

1. (a)Calculate the mass of sodium azide needed to fill a 36 dm³ airbag with nitrogen at r.t.p.[4]
2. (b)State one safety reason why the sodium produced must be dealt with by other chemicals in the mixture.[2]