Topic 5.1: How Much? The Amount of Chemical Change Questions

Calcium carbonate decomposes on heating: CaCO₃ → CaO + CO₂.

Calculate the mass of calcium oxide formed when 25.0 g of calcium carbonate decomposes completely.

(M(CaCO₃) = 100.09 g mol⁻¹, M(CaO) = 56.08 g mol⁻¹.) [3]

Hydrogen reacts with chlorine: H₂ + Cl₂ → 2HCl.

A mixture of 0.30 mol of hydrogen and 0.20 mol of chlorine is allowed to react.

Deduce the limiting reactant and state the amount, in moles, of hydrogen chloride formed. [3]

In the industrial preparation of titanium, TiCl₄ + 2Mg → Ti + 2MgCl₂, calculate the percentage atom economy for producing titanium.

(M: TiCl₄ = 189.68, Mg = 24.31, Ti = 47.87 g mol⁻¹.)

A student reacts 0.0500 mol of salicylic acid to make aspirin.

The balanced equation has a 1:1 mole ratio and the theoretical yield is 9.01 g of aspirin.

The student isolates 7.20 g of dry aspirin.

(a) Calculate the percentage yield.

(b) Suggest one reason the yield is below 100%.

Magnesium metal reacts with dilute hydrochloric acid to form aqueous magnesium chloride and hydrogen gas.

Write the balanced equation, including state symbols. [2]

Ammonia is produced in the Haber process: N₂(g) + 3 H₂(g) → 2 NH₃(g).

Calculate the amount, in mol, of ammonia produced when 0.90 mol of hydrogen reacts completely with excess nitrogen. [2]

50 cm³ of butane, C₄H₁₀, is burned completely. All gas volumes are measured at the same temperature and pressure (with water as a liquid). Calculate the volume of carbon dioxide produced. [2]

2C₄H₁₀(g) + 13O₂(g) → 8CO₂(g) + 10H₂O(l)

0.150 mol of zinc reacts completely with excess hydrochloric acid. Calculate the volume of hydrogen gas produced, measured at STP. (V_m = 22.7 dm³ mol⁻¹.) [3]

Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

A 25.0 cm³ sample of nitric acid, HNO₃, is exactly neutralised by 18.5 cm³ of 0.200 mol dm⁻³ sodium hydroxide, NaOH. Calculate the concentration of the nitric acid.

HNO₃ + NaOH → NaNO₃ + H₂O [3]

A 0.500 g sample of impure sodium carbonate, Na₂CO₃, is dissolved and reacted with 50.0 cm³ of 0.500 mol dm⁻³ HCl, which is in excess. The unreacted HCl is then titrated and found to be 6.00 × 10⁻³ mol. Calculate the amount, in mol, of HCl that reacted with the sodium carbonate.

Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂ [3]