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.
[2 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.
[2 marks]
5 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
A container holds 1.5 dm³ of a solution with concentration 8.0 g/dm³. The solvent evaporates and 1.0 dm³ remains. No solute is lost.
.1
Calculate the final concentration.
[3 marks]
.2
Explain why the concentration changes even though no solute is added.
[2 marks]
4 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
A pupil estimates the energy change for CH4+Cl2→CH3Cl+HCl. Bond energies are C-H 413, Cl-Cl 243, C-Cl 338 and H-Cl 431 kJ/mol.
.1
Calculate the energy change using only bonds that change.
[3 marks]
.2
Evaluate the claim that breaking the C-H bond supplies the energy released.
[1 mark]
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.
