A sodium hydroxide solution is added gradually to hydrochloric acid. Initially the acid has pH 1; later the mixture has pH 4.
.1
Calculate the initial hydrogen ion concentration divided by the later hydrogen ion concentration.
[2 marks]
.2
Explain the chemical change that removes hydrogen ions. Explain why pH 4 does not show complete neutralisation.
[2 marks]
5 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
An oxygen molecule contains two oxygen atoms. Each atom has six outer electrons.
.1
Explain the bonding needed for both atoms to achieve full outer shells.
[3 marks]
.2
Explain why a line drawing O=O does not show every electron.
[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]
5 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A filter designer chooses a single graphene sheet rather than a thick graphite block. Graphene consists of one layer of carbon atoms.
.1
Compare the structures and explain two resulting properties of graphene.
[3 marks]
.2
Explain why evidence for strength alone cannot establish that graphene is a suitable filter.
[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.
