Two separate samples each have mass 8.0 g. One is oxygen gas, O2, and the other is sulfur dioxide, SO2.Ar: O = 16, S = 32.
.1
Calculate the amount of oxygen molecules in the oxygen sample.
[2 marks]
.2
Calculate the amount of sulfur dioxide molecules in its sample.
[2 marks]
.3
Explain which sample contains more molecules and by what factor.
[2 marks]
6 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
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
Three noble gases have boiling points: helium −269 °C, neon −246 °C and argon −186 °C.
.1
Calculate the rise in boiling point from helium to argon.
[2 marks]
.2
Describe the trend and predict whether krypton, below argon, boils above or below −186 °C.
[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]
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.
