(a) The apparatus used for distillation is shown.
(i) Complete the box to name the apparatus. [1]
(ii) Describe and explain how the water is separated from the aqueous copper(II) sulfate by distillation. [3]
(b) A sample of solid hydrated copper(II) sulfate is heated gently in a test-tube.
\(CuSO_4.5H_2O \rightleftharpoons CuSO_4 + 5H_2O\)
hydrated copper(II) sulfate
Solid hydrated copper(II) sulfate is blue.
Describe two observations when the sample of solid hydrated copper(II) sulfate is heated gently in a test-tube.
1 ……………………………………………………………………………………………………………………………….
2 ……………………………………………………………………………………………………………………………….[2]
(c) Copper(II) sulfate can be prepared by heating an excess of copper(II) oxide with dilute sulfuric acid.
(i) Complete the chemical equation for this reaction.
\(CuO + H_2SO_4 \rightarrow CuSO_4 + …………………\)[1]
(ii) What method is used to separate the excess copper(II) oxide from the solution?
……………………………………………………………………………………………………………………… [1]
(d) Copper(II) oxide can be reduced by hydrogen.
\(CuO + H_2 \rightarrow Cu + H_2O\)
How does this equation show that copper(II) oxide is reduced?
………………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………………. [1]
(e) The chemical equation for the reaction of copper with concentrated nitric acid is shown.
\(Cu + 4HNO_3 \rightarrow Cu(NO_3)_2 + 2NO_2 + 2H_2O\)
Complete the word equation for this reaction.
▶️ Answer/Explanation
(a)(i) Ans: Liebig condenser
(a)(ii) Ans:
1. Water has a lower boiling point (100°C) than copper(II) sulfate, so it evaporates first.
2. The vapor passes through the condenser, where it cools and condenses back into liquid water.
3. Copper(II) sulfate remains in the flask as it has a much higher boiling point.
(b) Ans:
1. The blue hydrated copper(II) sulfate turns white as it loses water of crystallization.
2. Colorless water droplets form at the top of the test tube.
(c)(i) Ans: \(H_2O\) (water)
(c)(ii) Ans: Filtration (excess CuO is insoluble and can be filtered out)
(d) Ans: Copper(II) oxide loses oxygen (reduction = loss of oxygen).
(e) Ans: copper + nitric acid → copper nitrate + nitrogen dioxide + water
Rhenium is a metal.
(a) Describe three physical properties of rhenium.
(b) The structure of a rhenium chloride molecule is shown.
Determine the simplest formula for this chloride of rhenium.
(c) Rhenium oxide is a yellow solid which undergoes sublimation at a low temperature. What is the meaning of the term sublimation?
(d) Rhenium oxide reacts with water to form perrhenic acid. Perrhenic acid is strongly acidic.
(i) Which one of the following pH values represents an acidic solution? Draw a ring around the correct answer.
pH 2 pH 7 pH 9 pH 14
(ii) Perrhenic acid reacts with potassium hydroxide. Complete the word equation for this reaction.
(iii) Which one of the following compounds will react with perrhenic acid? Tick one box.
(e) Potassium perrhenate has a similar formula to potassium manganate(VII). Potassium manganate(VII) decomposes to give off oxygen. Describe a test for oxygen.
▶️ Answer/Explanation
(a) Ans: Any three of:
- High melting point (3180°C) – typical of transition metals
- Dense (21.0 g/cm³) – one of the densest elements
- Silver-gray metallic appearance
- Good electrical conductor
- Malleable and ductile
(b) Ans: ReCl3
The structure shows 1 rhenium atom bonded to 3 chlorine atoms, giving the simplest ratio of 1:3.
(c) Ans: Direct phase change from solid to gas without becoming liquid
Sublimation occurs when a solid’s vapor pressure exceeds atmospheric pressure before melting occurs.
(d)(i) Ans: pH 2
pH values below 7 indicate acidity, with lower numbers representing stronger acids.
(d)(ii) Ans: potassium perrhenate + water
Perrhenic acid (HReO4) neutralizes KOH in a typical acid-base reaction: HReO4 + KOH → KReO4 + H2O
(d)(iii) Ans: Potassium hydroxide (KOH)
As a base, KOH will react with the acidic perrhenic acid, unlike the other neutral/inert compounds listed.
(e) Ans: Glowing splint relights
Oxygen supports combustion, so inserting a glowing wooden splint into oxygen gas causes it to reignite brightly.