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) Three metals are placed in three different test-tubes of dilute sulfuric acid as shown in Fig. 11.1.
(i) Suggest the pH number of the dilute sulfuric acid.
pH = ……………………….
(ii) State which of the three metals in Fig. 11.1 reacts most quickly with dilute sulfuric acid.
(iii) When metals react with dilute sulfuric acid a gas is made. State the name of this gas.
(iv) A sulfuric acid molecule contains two hydrogen atoms, one sulfur atom and four oxygen
atoms. State the formula of sulfuric acid.
(b) Brass is an alloy.
(i) State what is meant by the term alloy.
(ii) A sample of brass has a mass of 250g. The sample of brass has the composition shown
in Table 11.1.
Calculate the mass of zinc contained in the sample of brass.
mass of zinc = ……………………………………………….g
(c) An isotope of zinc contains atoms which have a proton number of 30 and a nucleon number of 64.
(i) Complete the sentence to define the term isotope.
Isotopes are atoms of the same …………………………. which have the same …………………………. number but a different …………………………. number.
(ii) Deduce the number of electrons in this atom of zinc.
number of electrons = ………………………………..
(iii) Deduce the number of neutrons in this atom of zinc.
number of neutrons = …………………………………
(d) Zinc ore is a finite resource.
State what is meant by a finite resource.
▶Answer/Explanation
Ans:
11(a)(i) in the range from 1 to 6 ;
11(a)(ii) magnesium ;
11(a)(iii) hydrogen ;
11(a)(iv) H2SO4 ;
11(b)(i) a mixture of a metals and other elements;
11(b)(ii) 33 × 250 / 100 ;
83 ;
11(c)(i) element;
proton and nucleon;
11(c)(ii) 30 ;
11(c)(iii) 34 ;
11(d) (A finite resource is something useful that is) non-renewable / will eventually run out ;
Question
(a) Substances are separated from mixtures of substances using different methods.
Draw one straight line from each substance to the correct method of separating it from the mixture.
One line has been drawn for you.
(b) One reason for separating mixtures is to purify substances.
Explain the importance of purity in the manufacture of substances used in food additives.
(c) The element lead is obtained from the compound lead(II) bromide by electrolysis.
(i) Describe the difference between an element and a compound.
(ii) Complete the sentences to describe the electrolysis of lead(II) bromide.
Electrolysis is the breakdown of molten lead(II) bromide by the passage of ………………………………………… .
The gas released at the positive electrode is ………………………………………… and ………………………………………… is formed at the negative electrode.
The negative electrode is called the ………………………………………… .
(d) A student reacts dilute hydrochloric acid with four metals.
The student’s observations are shown in Table 5.1.
Place the four metals in order of their reactivity from the most reactive to the least reactive.
▶️Answer/Explanation
Ans : 5(a) 
5(b) to avoid poisoning ;
5(c)(i) element contains only one type of atom /
compound consists of (atoms of) two or more elements (chemically combined) ;
5(c)(ii) electricity ;
bromine and lead ;
cathode ;
5(d) calcium
magnesium
lead
copper
;;
Question
(a) The list below shows some chemical processes.
chlorination chromatography cracking
crystallisation decomposition
electrolysis fractional distillation polymerisation
Identify the process from the list that is used:
(i) in the treatment of drinking water
…………………………………………………………………………………………………………………….
(ii) to separate a mixture of dyes
…………………………………………………………………………………………………………………….
(iii) to extract aluminium from bauxite
…………………………………………………………………………………………………………………….
(iv) to produce long chain molecules from monomer units.
…………………………………………………………………………………………………………………….
(b) When dilute hydrochloric acid is added to aqueous sodium hydroxide, a neutralisation reaction occurs.
Fig. 2.1 shows apparatus used to investigate the change in pH as the acid is added.
(i) State the name of apparatus A.
…………………………………………………………………………………………………………………….
(ii) State the reading on the pH meter when the dilute hydrochloric acid exactly neutralises
the aqueous sodium hydroxide.
…………………………………………………………………………………………………………………….
(iii) State the two products of the reaction shown in Fig. 2.1.
1 ……………………………………………………………………………………………………………………….
2 ……………………………………………………………………………………………………………………….
(c) Describe what is observed when aqueous sodium hydroxide is added to blue copper(II) sulfate solution.
…………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………………
▶️Answer/Explanation
Ans: 2(a)(i) chlorination ;
2(a)(ii) chromatography ;
2(a)(iii) electrolysis ;
2(a)(iv) polymerisation ;
2(b)(i) burette ;
2(b)(ii) 7 ;
2(b)(iii) sodium chloride ;
water ;
2(c) pale blue precipitate ;
Question
(a) An atom of copper has a proton number of 29 and a nucleon number of 63.
(i) State the number of electrons in this copper atom. …………………………….
(ii) State the number of neutrons in this copper atom. …………………………….
(b) Copper oxide is heated with carbon. Copper and carbon dioxide are made.
(i) Write the word equation for this reaction.
(ii) In this reaction, reduction of copper in the copper oxide occurs.
Describe what is meant by the term reduction.
…………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………….
(iii) Explain why copper oxide is described as a basic oxide.
…………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………….
(c) Copper is a transition element.
Transition elements have high densities, high melting points and high boiling points. They are all metals.
State one other property of a transition element.
……………………………………………………………………………………………………………………..
……………………………………………………………………………………………………………………..
(d) (i) Brass is a mixture of copper and zinc.
State the term used to describe a mixture of metals.
…………………………………………………………………………………………………………………….
(ii) Brass is more malleable than either copper or zinc.
State the meaning of the term malleable.
…………………………………………………………………………………………………………………….
(iii) State the symbols of both copper and zinc.
copper symbol ……………………
zinc symbol ……………………
(e) A metal key is covered with a layer of copper by electroplating.
(i) The key is an electrode.
State which electrode is the key.
…………………………………………………………………………………………………………………….
(ii) Suggest a suitable electrolyte for electroplating the key.
…………………………………………………………………………………………………………………….
▶️Answer/Explanation
Ans: 8(a)(i) 29 ;
8(a)(ii) 34 ;
8(b)(i) copper oxide + carbon → copper + carbon dioxide ;
8(b)(ii) loss of oxygen ;
8(b)(iii) metal oxide / reacts with an acid to make a salt / neutralises an acid ;
8(c) any one from:
forms coloured compounds ;
acts as catalyst ; variable valency ;
8(d)(i) alloy ;
8(d)(ii) can be beaten into shape;
8(d)(iii) Cu and Zn ;
8(e)(i) cathode / negative ;
8(e)(ii) copper (II) sulfate ;
Question
(a) Potassium is an element in the Periodic Table. (Topic: C8)
Use numbers from the list to complete the sentences about potassium.
Each number may be used once, more than once, or not at all.
1 2 3 8 19 20 39
(i) Potassium is an element in group … of the Periodic Table. (Sub-topic: C8.1)
▶️Answer/Explanation
Potassium is an element in Group 1 of the Periodic Table because it is an alkali metal.
(ii) A potassium atom has a total of … electrons. (Sub-topic: C8.1)
▶️Answer/Explanation
A potassium atom has a total of 19 electrons because its atomic number is 19.
(iii) A potassium ion has a positive charge of …. (Sub-topic: C8.2)
▶️Answer/Explanation
A potassium ion has a positive charge of 1 because it loses one electron to form K⁺.
(b) Sodium and chlorine react to form sodium chloride. (Topic: C8)
Fig. 8.1 shows the electronic structure of a sodium atom and a chlorine atom.
(i) Complete the diagrams in Fig. 8.2 to show the electronic structure of the ions in sodium chloride. (Sub-topic: C8.2)
▶️Answer/Explanation
Sodium ion (Na⁺): 2,8 (lost one electron)
Chloride ion (Cl⁻): 2,8,8 (gained one electron)
This transfer of electrons forms an ionic bond.
(c) Fig. 8.3 shows the electrolysis of concentrated aqueous sodium chloride. (Topic: C4)
(i) Complete Fig. 8.3 by labelling the: (Sub-topic: C4.2)
- Anode
- Cathode
- Electrolyte
▶️Answer/Explanation
Anode (Positive Electrode): Where oxidation occurs
Cathode (Negative Electrode): Where reduction occurs
Electrolyte: Concentrated aqueous sodium chloride (NaCl solution).
(ii) Hydrogen gas is one of the electrode products of this electrolysis. State the name of the other electrode product. (Sub-topic: C4.2)
▶️Answer/Explanation
The other electrode product is chlorine gas (Cl₂), which is released at the anode.
(iii) Describe the chemical test for hydrogen gas. State the observation for a positive result. (Sub-topic: C4.3)
▶️Answer/Explanation
Test: Hold a lighted splint near the gas.
Observation: If hydrogen gas is present, it will produce a ‘pop’ sound as it burns.
Question
(a) Sodium and chlorine are elements.
Sodium chloride is a compound.
Describe what is meant by an element and a compound.
element …………………………………………………………………………………………………………………….
…………………………………………………………………………………………………………………………………
compound …………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
(b) Sodium reacts with chlorine to make sodium chloride.
Balance the symbol equation for this reaction.
………Na + Cl$_{2}$ ………NaCl
(c) When sodium reacts with chlorine, sodium atoms become sodium ions and chlorine atoms become chloride ions.
The electron configuration of a sodium atom is 2.8.1.
The electron configuration of a chlorine atom is 2.8.7.
State the electron configuration of a sodium ion and a chloride ion.
sodium ion ………………………………………..
chloride ion ………………………………………..
(d) Describe the difference in the solubility in water of an ionic compound compared with a covalent compound.
…………………………………………………………………………………………………………………………………
…………………………………………………………………………………………………………………………………
(e) Sodium chloride contains chloride ions.
Describe the test for chloride ions and state the observation for a positive result.
test …………………………………………………………………………………………………………………………..
observation ……………………………………………………………………………………………………………….
(f) Fig. 11.1 shows the electrolysis of concentrated aqueous sodium chloride.
Complete the sentences about the electrolysis of concentrated aqueous sodium chloride.
Electrolysis is defined as the breakdown of an ionic compound when
………………………………. or in aqueous solution by the passage of ……………………………….
The gas released at the negative electrode is ………………………………. and the gas
released at the positive electrode is ………………………………. .
▶️Answer/Explanation
Ans: 11(a) element – contains only one type of atom ;
compound – contains two or more elements (chemically combined) ;
11(b) 2Na + Cl$_{2}$ → 2NaCl ;
11(c) sodium ion 2.8 ;
chloride ion 2.8.8 ;
11(d) solubility of ionic compound is greater ;
11(e) add acidified aqueous silver nitrate ;
white precipitate ;
11(f) molten ;
electricity ;
hydrogen ;
chlorine ;
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.