GCSE Chemistry The mole questions by topic

Complete the sentences about the mole.

1. (a)One mole contains … × 10²³ particles.[1]
2. (b)The mass of one mole of a compound in grams equals its …[1]
3. (c)State the equation linking moles, mass and Mr.[1]
4. (d)Calculate the mass of 2 mol of CO₂ (C 12, O 16).[1]

Calculate the number of moles in each sample.

1. (a)24 g of carbon (C 12)[1]
2. (b)80 g of NaOH (Na 23, O 16, H 1)[1]
3. (c)8.8 g of CO₂ (C 12, O 16)[1]

Calcium carbonate thermally decomposes: CaCO₃ → CaO + CO₂.

1. (a)State the mole ratio of CaCO₃ to CaO.[1]
2. (b)Calculate the Mr of CaCO₃ (Ca 40, C 12, O 16).[1]
3. (c)Calculate the mass of CaO formed from 10 g of CaCO₃ (CaO: 56).[2]

A student weighs out 0.25 mol of sodium chloride for an experiment (Na 23, Cl 35.5).

1. (a)Calculate the Mr of NaCl.[1]
2. (b)Calculate the mass to weigh out.[1]
3. (c)State how many formula units are in the sample (to 3 significant figures).[1]

Iron reacts with sulfur: Fe + S → FeS. A mixture contains 5.6 g of iron and 3.2 g of sulfur (Fe 56, S 32).

1. (a)Calculate the moles of iron and of sulfur.[2]
2. (b)State which reactant is in excess and how much of it is left over.[2]

The table shows three samples. Complete the missing values (Avogadro constant = 6.02 × 10²³ per mole; H 1, C 12, O 16, Mg 24).

1. (a)Calculate the moles of CO₂.[1]
2. (b)Calculate the number of CO₂ molecules.[1]
3. (c)Calculate the moles of Mg.[1]
4. (d)Calculate the number of Mg atoms.[1]
5. (e)Explain why the 4.4 g and 1.2 g samples do not contain the same number of particles.[1]

Hydrogen burns in oxygen: 2H₂ + O₂ → 2H₂O (H 1, O 16). A balloon holds 1.0 g of hydrogen, which is burned completely.

1. (a)State the mole ratio of hydrogen to water in the equation.[1]
2. (b)Calculate the moles of hydrogen burned and the mass of water formed.[2]
3. (c)Calculate the mass of oxygen that reacts.[1]

Magnesium burns in air: 2Mg + O₂ → 2MgO (Mg 24, O 16).

1. (a)Calculate the mass of magnesium oxide formed by burning 6.0 g of magnesium in excess air.[3]
2. (b)Calculate the mass of oxygen that reacts in part (a).[2]
3. (c)Show that your two answers conserve mass.[1]

Titanium is extracted from titanium chloride: TiCl₄ + 2Mg → Ti + 2MgCl₂ (Ti 48, Cl 35.5, Mg 24).

1. (a)Calculate the mass of titanium formed from 38.0 g of TiCl₄ (Mr 190).[3]
2. (b)Calculate the mass of magnesium needed to react with all of it.[3]

A student adds 6.5 g of zinc to 100 cm³ of copper sulfate solution containing 12.8 g of copper sulfate (Zn 65, Cu 64, S 32, O 16). Zn + CuSO₄ → ZnSO₄ + Cu.

1. (a)Show which reactant is limiting.[4]
2. (b)Calculate the mass of copper displaced.[2]

Sodium hydrogencarbonate decomposes on heating: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂ (Na 23, H 1, C 12, O 16).

1. (a)Calculate the Mr of NaHCO₃.[1]
2. (b)Calculate the mass of Na₂CO₃ (Mr 106) formed from 8.4 g of NaHCO₃.[3]
3. (c)State the total mass of gas released.[2]

Carbon monoxide burns in oxygen: 2CO + O₂ → 2CO₂ (C 12, O 16). In a fume cupboard, 1.4 g of CO reacts with 4.48 dm³ of O₂ at RTP (molar volume 24 dm³).

1. (a)Calculate the moles of CO and of O₂.[2]
2. (b)Identify the limiting reactant.[1]
3. (c)Calculate the volume of CO₂ formed at RTP.[2]
4. (d)Calculate the mass of CO₂ formed.[1]

Aluminium burns in oxygen: 4Al + 3O₂ → 2Al₂O₃ (Al 27, O 16). A 2.7 g strip of aluminium is burned completely in excess oxygen.

1. (a)Calculate the mass of aluminium oxide formed.[3]
2. (b)Calculate the volume of oxygen consumed, in dm³ at RTP.[2]
3. (c)Explain why the product’s mass is greater than 2.7 g even though atoms are conserved.[1]

This question is about gas volumes at RTP (molar volume 24 dm³).

1. (a)Calculate the volume of 1.5 mol of oxygen.[1]
2. (b)Calculate the volume of CO₂ released when 20 g of calcium carbonate reacts with excess acid (CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂; Ca 40, C 12, O 16).[4]
3. (c)State the mass of that CO₂.[2]

Ammonia is made in the Haber process: N₂ + 3H₂ → 2NH₃ (N 14, H 1). A reactor is charged with 56 g of nitrogen and 18 g of hydrogen.

1. (a)Calculate the moles of each reactant.[2]
2. (b)Identify the limiting reactant, showing your comparison.[2]
3. (c)Calculate the maximum mass of ammonia formed.[3]

An ore contains iron(III) oxide, Fe₂O₃, reduced in a blast furnace by carbon monoxide: Fe₂O₃ + 3CO → 2Fe + 3CO₂ (Fe 56, O 16, C 12).

1. (a)Show which reactant is limiting.[4]
2. (b)Calculate the maximum mass of iron produced.[2]
3. (c)Calculate the mass of CO₂ released.[2]

Ammonium nitrate fertiliser is made by neutralising ammonia with nitric acid: NH₃ + HNO₃ → NH₄NO₃ (N 14, H 1, O 16). A plant produces 8.0 tonnes of ammonium nitrate per day.

1. (a)Calculate the Mr of ammonium nitrate.[1]
2. (b)Calculate the percentage by mass of nitrogen in ammonium nitrate.[2]
3. (c)Calculate the mass of ammonia needed each day (in tonnes).[3]
4. (d)Calculate the mass of nitric acid needed each day (in tonnes).[2]

A class collects the hydrogen from magnesium reacting with excess dilute hydrochloric acid: Mg + 2HCl → MgCl₂ + H₂ (Mg 24; molar volume 24 dm³). The students add 0.24 g of magnesium and collect 225 cm³ of gas in a gas syringe.

1. (a)Calculate the volume of hydrogen predicted by the equation.[3]
2. (b)Calculate the collected volume as a percentage of the predicted volume.[2]
3. (c)Suggest two reasons why the collected volume is less than predicted.[2]
4. (d)State whether the mass difference shows conservation of mass has been broken, and why.[1]