GCSE Combined Science Quantitative chemistry questions by topic

A sealed flask contains 10 g of reactants. After the reaction, the flask and contents still weigh 10 g.

1. (a)Name the law this demonstrates.[1]
2. (b)Explain why the mass does not change.[2]
3. (c)State what would happen to the measured mass if the flask were open and a gas formed.[1]

Write the missing balancing numbers for these equations.

1. (a)H₂ + O₂ → H₂O[1]
2. (b)Na + Cl₂ → NaCl[1]
3. (c)CH₄ + O₂ → CO₂ + H₂O[2]

Work out the relative formula mass of each compound (Na = 23, O = 16, H = 1, C = 12, Ca = 40).

1. (a)H₂O[1]
2. (b)CO₂[1]
3. (c)NaOH[1]
4. (d)CaCO₃[1]

A solution contains 12 g of sugar in 300 cm³ of solution.

1. (a)Convert 300 cm³ to dm³.[1]
2. (b)Calculate the concentration of the sugar solution.[2]
3. (c)State what happens to the concentration if more water is added.[1]

This question uses the equation: 2Na + Cl₂ → 2NaCl (Ar Na = 23, Ar Cl = 35.5).

1. (a)Calculate the Mr of NaCl.[1]
2. (b)Calculate the moles of Na in 4.6 g.[2]
3. (c)Calculate the mass of NaCl formed from 4.6 g of Na.[2]

Explain these observations about mass.

1. (a)A piece of magnesium burned in a crucible weighs more afterwards.[2]
2. (b)An effervescent tablet fizzing in water on a balance weighs less afterwards.[2]

A student measures the volume of gas collected in five identical reactions.

1. (a)Calculate the mean volume.[2]
2. (b)Estimate the uncertainty of the mean.[2]

Complete and balance: CaCO₃ → CaO + CO₂ (used in the lime kiln).

1. (a)Show the equation is already balanced, by tallying each element.[2]
2. (b)Add the state symbols: calcium carbonate (solid), calcium oxide (solid), carbon dioxide (gas).[1]
3. (c)Explain why 100 g of CaCO₃ produces 44 g of CO₂ and 56 g of CaO.[1]

This question uses: Fe₂O₃ + 3CO → 2Fe + 3CO₂ (Ar Fe = 56, C = 12, O = 16).

1. (a)Calculate the Mr of Fe₂O₃.[1]
2. (b)Calculate the moles of Fe₂O₃ in 320 g.[2]
3. (c)Calculate the maximum mass of iron produced from 320 g of Fe₂O₃.[3]

This question uses: N₂ + 3H₂ → 2NH₃ (Ar N = 14, H = 1).

1. (a)Calculate the moles of H₂ in 1.2 g.[2]
2. (b)Determine which reactant is limiting if 6.0 g of N₂ is also present, showing your working.[2]
3. (c)Calculate the maximum mass of ammonia formed.[1]

A titration-style measurement gives titre values of 24.6, 25.0 and 25.4 cm³ across three trials.

1. (a)Calculate the mean and its uncertainty.[3]
2. (b)Explain why repeating improves confidence in the result.[2]
3. (c)The same solution measured 26.5 cm³ on a fourth trial. State what should be done and why.[1]

Explain the chemistry behind “just add water” hand-warmer reactions that dissolve solid calcium chloride, then link to concentration.

1. (a)Explain why dissolving is a physical change, not a chemical reaction.[2]
2. (b)A pack dissolves 20 g of CaCl₂ in 80 cm³ of water. Calculate the concentration in g/dm³.[2]