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]
4 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A solid expected to melt sharply at 156 °C instead melts over 148-153 °C. Its chromatogram shows one visible spot in one solvent.
Evaluate the claim that the single spot proves the solid is pure.
[4 marks]
4 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
An equilibrium mixture follows P+Q⇌R in solution. A process continuously removes R while fresh P and Q are supplied. Temperature is constant.
Explain why product removal can increase the total amount of R collected, and why this is not evidence that the equilibrium reaction has become irreversible.
[4 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
A steel object of mass 45.0 g is left in damp air. After all loose material is retained, the object and corrosion products have mass 47.7 g.
.1
Calculate the percentage increase in mass.
[3 marks]
.2
Explain why the increase does not contradict conservation of mass.
