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]
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]
6 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
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]
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]
7 marksHigher
Spec and skills
Original practice question
Answer and supported method checks
A student measures a beaker as 42.36 g empty and 47.82 g with a dry solid. Each balance reading has uncertainty ±0.01 g. Add absolute uncertainties for a mass found by subtraction.
.1
Calculate the mass of solid.
[2 marks]
.2
Calculate the percentage uncertainty in the solid mass.
[3 marks]
.3
Suggest how a larger mass of the same solid affects percentage uncertainty with this balance.
