Chemistry
Stoichiometry — Topics 1 and 4
- 1.
Calculate the number of moles in 5.85 g of sodium chloride, NaCl. Use Ar: Na = 23.0, Cl = 35.5.
[3 marks] - 2.
Magnesium reacts with hydrochloric acid: Mg + 2HCl → MgCl₂ + H₂. Identify the limiting reactant when 0.10 mol Mg reacts with 0.15 mol HCl, and calculate the amount of hydrogen formed.
[4 marks] - 3.
Calculate the relative formula mass (Mr) of calcium carbonate, CaCO₃. Use Ar: Ca = 40, C = 12, O = 16.
[2 marks] - 4.
Calculate the percentage by mass of oxygen in magnesium oxide, MgO. Use Ar: Mg = 24, O = 16.
[3 marks] - 5.
Calculate the volume, in dm³, occupied by 0.50 mol of carbon dioxide gas at room temperature and pressure (rtp), given that 1 mole of gas occupies 24 dm³ at rtp.
[2 marks] - 6.
Calculate the empirical formula of a compound containing 40% carbon, 6.7% hydrogen and 53.3% oxygen by mass. Use Ar: C = 12, H = 1, O = 16.
[4 marks] - 7.
A student dilutes 20.0 cm³ of 2.0 mol/dm³ hydrochloric acid to a total volume of 100 cm³. Calculate the new concentration of the diluted acid.
[3 marks] - 8.
State Avogadro's constant and use it to calculate the number of molecules in 0.25 mol of water.
[3 marks] - 9.
Sodium carbonate reacts with hydrochloric acid: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂. Calculate the mass of sodium carbonate needed to react exactly with 0.20 mol of hydrochloric acid. Use Ar: Na = 23, C = 12, O = 16.
[4 marks] - 10.
Explain why the actual (experimental) yield of a chemical reaction is usually less than the theoretical yield calculated from the balanced equation.
[3 marks] · no calculator - 11.
25.0 cm³ of sodium hydroxide solution is exactly neutralised by 20.0 cm³ of 0.15 mol/dm³ hydrochloric acid: NaOH + HCl → NaCl + H₂O. Calculate the concentration of the sodium hydroxide solution.
[3 marks] - 12.
A 2.50 g sample of hydrated copper(II) sulfate, CuSO₄·xH₂O, is heated to constant mass, leaving 1.60 g of anhydrous copper(II) sulfate. Calculate the value of x. Use Mr: CuSO₄ = 160, H₂O = 18.
[4 marks] - 13.
Calcium carbonate decomposes on heating: CaCO₃ → CaO + CO₂. Calculate the mass of calcium oxide produced from 25.0 g of calcium carbonate. Use Mr: CaCO₃ = 100, CaO = 56.
[3 marks] - 14.
Zinc reacts with excess hydrochloric acid: Zn + 2HCl → ZnCl₂ + H₂. Calculate the volume of hydrogen gas produced at room temperature and pressure (rtp) from 6.5 g of zinc. Use Ar: Zn = 65; 1 mole of gas occupies 24 dm³ at rtp.
[4 marks] - 15.
A solution of sodium hydroxide has a concentration of 8.0 g/dm³. Calculate its concentration in mol/dm³. Use Mr: NaOH = 40.
[2 marks] - 16.
0.20 mol of magnesium is reacted with 0.30 mol of hydrochloric acid: Mg + 2HCl → MgCl₂ + H₂. Determine which reactant is in excess, and calculate how many moles of it remain unreacted.
[4 marks] - 17.
25.0 cm³ of 0.20 mol/dm³ sodium hydroxide solution is exactly neutralised by 15.0 cm³ of sulfuric acid: H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O. Calculate the concentration of the sulfuric acid.
[4 marks] - 18.
A student calculates a theoretical yield of 12.0 g for a preparation, but obtains an actual yield of 9.6 g. Calculate the percentage yield.
[2 marks] - 19.
2 dm³ of hydrogen gas react completely with 1 dm³ of oxygen gas to form water vapour: 2H₂ + O₂ → 2H₂O. State the law that explains why the ratio of reacting gas volumes matches the ratio of moles in the equation, and calculate the volume of oxygen needed to react completely with 10 dm³ of hydrogen.
[3 marks] - 20.
Calculate the number of moles of solute in 250 cm³ of a 0.40 mol/dm³ solution of potassium nitrate.
[2 marks] - 21.
Calculate the mass of sodium hydroxide needed to prepare 500 cm³ of a 0.20 mol/dm³ solution. Use Mr: NaOH = 40.
[3 marks] - 22.
180 cm³ of oxygen gas at room temperature and pressure (rtp) reacts completely with excess magnesium: 2Mg + O₂ → 2MgO. Calculate the mass of magnesium oxide formed. Use Ar: Mg = 24, O = 16; 1 mole of gas occupies 24 dm³ at rtp.
[5 marks] - 23.
A 0.50 mol sample of a compound has a mass of 45 g. Calculate its relative formula mass (Mr).
[2 marks] - 24.
Calculate the volume of 0.50 mol/dm³ hydrochloric acid required to react exactly with 2.65 g of sodium carbonate: Na₂CO₃ + 2HCl → 2NaCl + H₂O + CO₂. Use Mr: Na₂CO₃ = 106.
[4 marks] - 25.
Calculate the percentage by mass of water in hydrated magnesium sulfate, MgSO₄·7H₂O. Use Ar: Mg = 24, S = 32, O = 16, H = 1.
[4 marks]