CIE iGCSE Co-Ordinated Science C4.1 Electrolysis Exam Style Questions Paper 3
Question
(a) Copper is a metal in high demand that is now often recycled.
To recycle copper, it must be melted down into a liquid.
(i) Suggest one reason other than cost why copper and other metals are recycled.
(ii) Describe two differences between the arrangement and motion of atoms in molten
copper and the arrangement and motion of atoms in solid copper.
(b) A metal coin is covered with a layer of copper by electroplating.
(i) The coin is used as one of the electrodes.
State for which electrode the coin is used.
(ii) Suggest a suitable solution to be used as the electrolyte for electroplating the coin.
(iii) Electroplating uses the process of electrolysis; a definition is provided.
Electrolysis is the breakdown of a covalent compound when solid or in aqueous solution by the passage of electricity.
This definition of electrolysis is not correct.
Circle the two words in the definition that are not correct.
▶️Answer/Explanation
Ans : 8(a)(i) copper (ore) is a finite resource ;
8(a)(ii) arrangement – solid regular and liquid irregular ;
motion – solid vibrate (about fixed point) only / do not move AND liquid are able to move about ;
8(b)(i) cathode ;
8(b)(ii) copper sulfate / copper chloride ;
8(b)(iii) covalent ;
solid ;
Question
(a) Fig. 8.1 shows the electrolysis of molten lead(II) bromide.
(i) State the name of the electrode where lead is made.
▶️Answer/Explanation
Answer: cathode
Explanation: During the electrolysis of molten lead(II) bromide, lead ions (Pb2+) gain electrons at the cathode to form lead metal. Therefore, lead is made at the cathode.
(ii) Explain why an orange gas is seen above the molten lead(II) bromide.
▶️Answer/Explanation
Answer: Bromine (vapour) is released.
Explanation: During the electrolysis, bromide ions (Br–) lose electrons at the anode to form bromine gas (Br2). Bromine gas is orange in color, which is why an orange gas is seen above the molten lead(II) bromide.
(b) Lead is extracted from lead oxide by reaction with carbon. The equation for the reaction is shown.
lead oxide + carbon → lead + carbon dioxide
Name the substance that is oxidised and the substance that is reduced in this reaction.
▶️Answer/Explanation
Answer: Oxidised: carbon; Reduced: lead oxide
Explanation: In this reaction, carbon is oxidised because it gains oxygen to form carbon dioxide. Lead oxide is reduced because it loses oxygen to form lead metal.
(c) Lead is a metal. Suggest one test to show that lead is a metal.
▶️Answer/Explanation
Answer: Test for electrical conductivity.
Explanation: Metals are good conductors of electricity. A simple test to show that lead is a metal is to check if it conducts electricity. If it does, it confirms that lead is a metal.
(d) Lead reacts very slowly with dilute sulfuric acid. State two ways of increasing the rate of reaction between lead and dilute sulfuric acid.
▶️Answer/Explanation
Answer: Increase temperature; Increase surface area of lead.
Explanation: The rate of reaction can be increased by increasing the temperature, which provides more energy for the particles to collide more frequently and with greater energy. Additionally, increasing the surface area of the lead (e.g., by using lead powder instead of a solid block) allows more particles to be exposed to the acid, increasing the rate of reaction.