This set mixes the five skills from chemical reasoning in mixed tasks. The questions run from easy to harder, and all data is invented. Use these relative atomic masses where needed: Cu = 64, C = 12, O = 16.
Write each answer on paper first, with units, then open the worked solution. Questions are labelled by skill, not by marks.
Questions
Q1 (easy, particle model). Which state of matter has particles that are far apart and move quickly in all directions? Describe the movement of particles in a solid.
Show answer
A gas has particles far apart that move quickly in all directions. In a solid the particles are close together in fixed positions and only vibrate.
Q2 (easy, cooling data). A liquid cools: 80 °C at 0 min, 70 °C at 2 min and 62 °C at 4 min. Find the mean cooling rate from 0 to 4 minutes.
Show answer
Fall = 80 − 62 = 18 °C over 4 min. Rate = 18 ÷ 4 = 4.5 °C/min.
Q3 (easy, particle model). Explain why a gas fills the whole container it is in.
Show answer
The particles in a gas move quickly in all directions and have very weak attractions between them, so they spread out until they fill the available space.
Q4 (medium, mass change). A 4.96 g sample of CuCO₃ is heated until complete: CuCO₃ → CuO + CO₂. Find the mass of CO₂ released and the mass of solid left.
Show answer
Moles of CuCO₃ = 4.96 ÷ 124 = 0.0400 mol. Ratio 1 : 1 : 1. Mass of CO₂ = 0.0400 × 44 = 1.76 g. Mass of CuO = 0.0400 × 80 = 3.20 g. Check: 1.76 + 3.20 = 4.96 g.
Q5 (medium, mass change). A student heats CuCO₃ until complete and finds the solid has lost 0.66 g. What mass of CuCO₃ was heated?
Show answer
Mass lost is CO₂. Moles of CO₂ = 0.66 ÷ 44 = 0.015 mol. Ratio 1 : 1, so 0.015 mol of CuCO₃. Mass = 0.015 × 124 = 1.86 g.
Q6 (medium, separation). A 250 cm³ sample of river water gives 3.0 g of dried mud. Find the concentration of mud in g/dm³.
Show answer
250 cm³ = 0.250 dm³. Concentration = 3.0 ÷ 0.250 = 12 g/dm³. Check: 12 × 0.250 = 3.0 g.
Q7 (medium, separation sequence). A sample contains sand, a layer of oil on top and dissolved salt. Give a sequence of methods to obtain pure water, with a reason for each.
Show answer
- Separating funnel (or skimming) to remove the oil, because it does not mix with water and floats.
- Filtration to remove the sand, because it is insoluble and too large to pass through the paper.
- Distillation of the filtrate, because water boils off and is condensed and collected, while the dissolved salt stays behind.
Q8 (harder, acidity). A gas dissolved in distilled water gives a solution with pH 4.0. What class of substance does this suggest, and what should you say about certainty?
Show answer
pH 4.0 is below 7, so the solution is acidic. This suggests an acidic oxide (a non-metal oxide). It supports the class but does not identify the exact gas, and one reading is weaker than repeated readings that agree.
Q9 (harder, repeats). Three titres are 18.6 cm³, 18.8 cm³ and 18.7 cm³. Find the mean and say whether the results agree.
Show answer
Sum = 18.6 + 18.8 + 18.7 = 56.1. Mean = 56.1 ÷ 3 = 18.7 cm³. The values are within 0.2 cm³ of each other, so they agree and the mean is reliable.
Q10 (harder, observation and inference). A solution gives a white precipitate with acidified silver nitrate, and a blue precipitate with sodium hydroxide. Write two observations and two inferences, and give the formula of the compound.
Show answer
Observations: a white precipitate formed with acidified silver nitrate; a blue precipitate formed with sodium hydroxide. Inferences: chloride ions are present; copper(II) ions are present. The compound is CuCl₂ because 2+ is balanced by two 1− ions.
If you got these wrong
- Q1 to Q3 wrong: revisit using a particle model to explain a state observation.
- Q4 or Q5 wrong: check the formula mass beside each substance in connecting an equation with a supplied mass change.
- Q6 or Q7 wrong: check unit conversion and the match between method and difference in interpreting a separation sequence.
- Q8 or Q9 wrong: see linking acidity evidence with a proposed substance class.
- Q10 wrong: practise the two columns in distinguishing observation from inference.
Record each error in the mistake log and retest queue, and use the scientific investigation critic to review your method wording. For reasoning checked against the 0653 scope, see online one-to-one Combined Science tuition.