Home / iGCSE Chemistry (0620) Theory (Core):6.1 Physical and chemical changes: Exam Style Questions Paper 3

iGCSE Chemistry (0620) Theory (Core):6.1 Physical and chemical changes: Exam Style Questions Paper 3- New Syllabus

iGCSE Chemistry Theory (Core) Paper 3 - All Chapters

Question

Fig. 7.1 shows the apparatus used to electrolyse dilute sulfuric acid using inert electrodes.
(a) State what is meant by the term electrolysis.
(b) Label the cathode in Fig. 7.1.
(c) Name one product formed at the anode.
(d) The inert electrodes used are made of graphite.
(i) Explain what is meant by the term inert.
(ii) State one other use for graphite. 
(e) Excess solid copper(II) carbonate is added to dilute sulfuric acid.
Aqueous copper(II) sulfate, water and carbon dioxide gas are produced.
(i) State with a reason if this is a chemical or a physical change.
(ii) Name a method to remove the excess copper(II) carbonate from the mixture.
(iii) Name one other substance which can be added to dilute sulfuric acid to form aqueous copper(II) sulfate.
(f) Copper(II) sulfate, $\mathrm{CuSO}_4$, exists in different forms.
Draw one line from each form of copper(II) sulfate to its description.

Most-appropriate topic codes (Cambridge IGCSE Chemistry 0620):

• Topic 4.1 — Electrolysis: Definition, electrodes, products (Parts a, b, c)
• Topic 2.6 — Giant covalent structures: Graphite properties and uses (Part d)
• Topic 6.1, 7.3 — Chemical changes, Salt preparation (Part e)
• Topic 7.3 — Water of crystallisation (Part f)

▶️ Answer/Explanation

(a) the decomposition of an ionic compound (when molten or in aqueous solution) by the passage of an electric current

Electrolysis uses an external source of electrical energy to drive a non-spontaneous decomposition reaction of an ionic substance.

(b) negative electrode labelled

The cathode is the electrode connected to the negative terminal of the power supply. It attracts positive cations.

(c) oxygen

In the electrolysis of dilute sulfuric acid with inert electrodes, hydroxide ions ($\mathrm{OH}^-$) from the water are preferentially discharged at the anode to form water and oxygen gas.

(d)(i) unreactive / does not react

An inert electrode serves only as a conductor of electricity and does not chemically participate in the electrolysis reactions, preventing contamination of the products.

(d)(ii) lubricant

Graphite has a layered structure with weak forces between layers, allowing them to slide easily, making it useful as a dry lubricant. It is also used as an electrode material due to its conductivity.

(e)(i) chemical change AND new substances are made

The reaction between copper(II) carbonate and sulfuric acid produces new substances (copper(II) sulfate, water, carbon dioxide) with different properties from the reactants, defining a chemical change.

(e)(ii) filtration

Filtration is used to separate an insoluble solid (excess copper(II) carbonate) from a liquid/solution (aqueous copper(II) sulfate).

(e)(iii) copper oxide / copper hydroxide

Both copper(II) oxide (an insoluble base) and copper(II) hydroxide (an alkali) will react with sulfuric acid in a neutralisation reaction to produce copper(II) sulfate and water.

(f)

“Anhydrous” means without water, “hydrated” means with water of crystallisation incorporated into the solid structure, and “aqueous” means dissolved in water to form a solution.

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