Sewage enters a treatment works containing rags, grit, suspended organic solids and dissolved organic material. A student proposes only filtration followed by chlorination.
Explain a more complete sewage-treatment sequence and the roles of microorganisms.
[4 marks]
4 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
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]
6 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
Students compare two catalysts for the decomposition of hydrogen peroxide. Each trial lasts 60 s; the same solution volume and concentration are available.
Plan an investigation to compare the rates fairly and assess whether a catalyst is used up.
[6 marks]
4 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A polymer model contains 150 chains. Each chain contains 400 repeat units.
.1
Calculate the total number of repeat units represented.
[2 marks]
.2
Explain why this model represents a polymer rather than a giant covalent lattice.
[2 marks]
4 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
A refinery has 60 tonnes of a long-chain fraction but buyers want only 20 tonnes. Catalytic cracking converts 75% of the 40-tonne surplus into shorter fuel molecules; the rest becomes other useful products.
.1
Calculate the mass of shorter fuel molecules obtained from the surplus.
[2 marks]
.2
Explain why cracking is useful and state one chemical test that distinguishes an alkene product from an alkane.
