Dilute hydrochloric acid is added to excess copper oxide. The black oxide becomes a blue-green copper chloride solution, with black solid remaining.
.1
Write the balanced equation.
[2 marks]
.2
Explain why excess copper oxide is used and how it is removed.
[2 marks]
.3
Explain why the mass of wet crystals would overestimate the mass of salt recovered.
[2 marks]
5 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
Two colourless liquids form a mixture. Liquid A boils at 56 °C and liquid B at 100 °C. A student wants to collect the liquid richer in A.
.1
Explain how fractional distillation separates the liquids.
[3 marks]
.2
Explain why one collected fraction is not guaranteed to be perfectly pure.
[2 marks]
7 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
A student measures a beaker as 42.36 g empty and 47.82 g with a dry solid. Each balance reading has uncertainty ±0.01 g. Add absolute uncertainties for a mass found by subtraction.
.1
Calculate the mass of solid.
[2 marks]
.2
Calculate the percentage uncertainty in the solid mass.
[3 marks]
.3
Suggest how a larger mass of the same solid affects percentage uncertainty with this balance.
[2 marks]
6 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A factory uses electrolysis to extract aluminium. One operating mixture needs 1200 energy units per batch; adding cryolite reduces the requirement to 900 units per equal batch.
.1
Calculate the percentage reduction in energy use.
[3 marks]
.2
Explain how cryolite reduces energy use and why the positive electrodes need replacement.
[3 marks]
5 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
Chlorine atoms have electron arrangement 2,8,7. Iodine atoms have more occupied electron shells but also seven outer electrons.
.1
Explain why chlorine is more reactive than iodine.
[3 marks]
.2
Compare this trend with the reactivity trend down group 1.
