ESAT Chemistry: Electrochemistry and organic chemistry, set 1

• Answer all questions. No calculator.
• Each question has exactly one correct answer.

1. 11 mark

   During the electrolysis of molten zinc chloride, two electrodes are dipped into the molten compound and connected to a battery.

   Which statement correctly matches the terms cathode, anode and electrolyte to their meanings?

   1. A The cathode is the positive electrode, the anode is the negative electrode, and the electrolyte is the substance being electrolysed.
   2. B The cathode is the negative electrode, the anode is the positive electrode, and the electrolyte is the substance being electrolysed.
   3. C The cathode is the negative electrode, the anode is the positive electrode, and the electrolyte is the metal rod carrying current into the cell.
   4. D The anode is the negative electrode, the cathode is the positive electrode, and the electrolyte is the battery supplying the current.
2. 21 mark

   Electrolysis cells are always connected to a direct current (dc) supply rather than an alternating current (ac) supply.

   Which of the following best explains why dc, and not ac, is used?

   1. A A dc supply produces a higher voltage than an ac supply of the same power rating, and electrolysis needs the higher voltage to break ionic bonds.
   2. B An ac supply cannot pass through a liquid or molten electrolyte at all, so no current would flow if ac were used.
   3. C A dc supply keeps each electrode permanently either positive or negative, so ions are attracted consistently to one electrode; an ac supply would reverse polarity many times a second, so ions would be pulled back and forth without net discharge.
   4. D A dc supply is needed because electrolytes only conduct electricity when the current flows in pulses, which only a dc supply produces.
3. 31 mark

   Molten lead(II) bromide, PbBr2, is electrolysed using inert electrodes.

   Which row correctly describes what happens at each electrode?

   1. A At the cathode, Pb2+ ions lose electrons (oxidation) to form lead metal; at the anode, Br- ions gain electrons (reduction) to form bromine.
   2. B At the cathode, Pb2+ ions gain electrons (reduction) to form lead metal; at the anode, Br- ions lose electrons (oxidation) to form bromine.
   3. C At the cathode, Br- ions gain electrons (reduction) to form bromine; at the anode, Pb2+ ions lose electrons (oxidation) to form lead metal.
   4. D At the cathode, Pb2+ ions gain electrons (reduction) to form lead metal; at the anode, Br- ions also gain electrons (reduction) to form bromine.
4. 41 mark

   Aqueous copper(II) sulfate is electrolysed using inert (graphite) electrodes.

   At the cathode, copper metal is deposited rather than hydrogen gas being produced.

   Which half-equation correctly represents the reaction taking place at the cathode?

   1. A Cu2+ + 2e- -> Cu
   2. B Cu2+ -> Cu + 2e-
   3. C Cu -> Cu2+ + 2e-
   4. D 2H+ + 2e- -> H2
5. 51 mark

   A steel spoon is to be electroplated with a thin layer of silver.

   Which of the following correctly describes how this is achieved, and why it might be done?

   1. A The spoon is made the cathode in a cell containing a solution of silver ions, with a silver anode; silver ions are reduced onto the spoon's surface, which can improve its appearance and resistance to corrosion.
   2. B The spoon is made the anode in a cell containing a solution of silver ions, with a silver cathode; silver ions are oxidised onto the spoon's surface.
   3. C The spoon is dipped directly into molten silver, and no electric current is needed for the silver to coat it.
   4. D The spoon is made the cathode in a cell containing a solution of silver ions, with a silver anode; silver ions are oxidised onto the spoon's surface.
6. 61 mark

   Propane, C3H8, is a member of the alkane homologous series.

   Which equation correctly represents the complete combustion of propane?

   1. A C3H8 + 5O2 -> 3CO + 4H2O
   2. B C3H8 + 3O2 -> 3CO2 + 4H2O
   3. C C3H8 + 5O2 -> 3CO2 + 4H2O
   4. D C3H8 + 5O2 -> 3CO2 + 4H2
7. 71 mark

   But-2-ene, an alkene with the formula C4H8, is shaken with orange bromine water.

   Which statement correctly describes what is observed, and why?

   1. A The bromine water turns from orange to colourless, because the C=C double bond in but-2-ene opens up and adds across the bromine molecule to form a colourless dibromo compound.
   2. B The bromine water stays orange, because alkenes such as but-2-ene have no reactive double bond available for addition reactions.
   3. C The bromine water turns from orange to colourless, because but-2-ene reacts with bromine in a substitution reaction, replacing a hydrogen atom with a bromine atom.
   4. D The bromine water turns blue, because but-2-ene reduces the bromine to bromide ions, which form a blue complex in water.
8. 81 mark

   A long-chain alkane, C16H34, is cracked using a catalyst and a high temperature to produce two shorter molecules, one of which is octane, C8H18.

   Which equation correctly represents this cracking reaction?

   1. A C16H34 -> C8H18 + C8H18
   2. B C16H34 -> C8H18 + C8H14
   3. C C16H34 -> C8H18 + C8H16
   4. D C16H34 -> 2C8H17
9. 91 mark

   Chloroethene, CH2=CHCl, is used as the monomer to make a common polymer by addition polymerisation.

   Which structure correctly represents the repeating unit of this polymer?

   1. A [-CH2-CH2-]n, formed by the chlorine atom being lost from the monomer as HCl gas before the remaining CH2=CH2 units join together.
   2. B [-CHCl-CHCl-]n, formed by two chlorine atoms being retained on the same repeating unit, with no hydrogen atoms remaining.
   3. C A polymer chain formed as -CH2-CHCl- units join with water released at every joint, in the same way that proteins form from amino acids.
   4. D [-CH2-CHCl-]n, formed by the C=C double bond opening so each monomer bonds to the next through single carbon-carbon bonds, with the chlorine atom retained on every repeating unit.
10. 101 mark

    Amino acid molecules join together by condensation polymerisation to form proteins, releasing a small molecule at each new bond formed.

    Which statement correctly describes this process?

    1. A Each new bond between two amino acids is formed with the loss of one molecule of hydrogen gas, and the resulting polymer is an addition polymer.
    2. B Each new bond between two amino acids is formed by the amino acids simply joining with no atoms lost at all, in exactly the same way as an alkene monomer forms an addition polymer.
    3. C Each new bond between two amino acids is formed with the loss of one molecule of water, and the resulting polymer is called a polypeptide (protein) chain.
    4. D Each new bond between two amino acids is formed with the loss of one molecule of carbon dioxide, releasing this gas as the protein forms.
11. 111 mark

    Propan-1-ol, an alcohol with the formula C3H7OH, is reacted with a small piece of sodium metal.

    Which statement correctly describes the general formula of alcohols and what is observed in this reaction?

    1. A Alcohols have the general formula CnH2n+2; sodium reacts with propan-1-ol to give off bubbles of oxygen gas.
    2. B Alcohols have the general formula CnH2n+1OH; sodium reacts with propan-1-ol to give off bubbles of hydrogen gas, as the metal displaces hydrogen from the -OH group.
    3. C Alcohols have the general formula CnH2n+1OH; sodium does not react with alcohols at all, since alcohols are not acidic.
    4. D Alcohols have the general formula CnH2nOH; sodium reacts with propan-1-ol to give off bubbles of carbon dioxide gas.
12. 121 mark

    Ethanoic acid, CH3COOH, is reacted with ethanol, C2H5OH, in the presence of a small amount of concentrated sulfuric acid as a catalyst.

    Which statement correctly describes carboxylic acids and the product of this reaction?

    1. A Carboxylic acids are strong acids, fully ionising in water; ethanoic acid reacts with ethanol to form an ester and water.
    2. B Carboxylic acids are weak acids; ethanoic acid reacts with ethanol to form an ester (ethyl ethanoate) and water.
    3. C Carboxylic acids are weak acids; ethanoic acid reacts with ethanol to form a salt and hydrogen gas, in the same way a metal reacts with an acid.
    4. D Carboxylic acids are weak acids; ethanoic acid reacts with ethanol to form an alcohol and carbon dioxide.
13. 131 mark

    Three metals, X, Y and Z, are tested with solutions of each other's ions.

    Metal X displaces both Y and Z from solutions of their salts. Metal Y displaces Z from a solution of its salt, but Y does not displace X. Metal Z displaces neither X nor Y.

    Which row correctly places these metals in order of decreasing reactivity, and links reactivity to how easily each metal's ions form?

    1. A Most to least reactive: Z, Y, X. The most reactive metal, Z, forms its positive ions least easily, which is why it can displace the other two metals from their salt solutions.
    2. B Most to least reactive: X, Y, Z. The most reactive metal, X, forms its positive ions least easily, which is why it can displace the other two, less reactive, metals from their salt solutions.
    3. C Most to least reactive: X, Y, Z. The most reactive metal, X, forms its positive ions most easily, which is why it can displace the other two, less reactive, metals from their salt solutions.
    4. D Most to least reactive: Y, X, Z. The most reactive metal, Y, forms its positive ions most easily, which is why it displaces Z but not X.
14. 141 mark

    Which statement correctly links a metal's physical or chemical properties to one of its everyday uses?

    1. A Aluminium is used in overhead power cables because it is denser than copper, making the cables hang in a straighter line between pylons.
    2. B Gold is used in some electrical connectors because it is highly reactive and readily forms an oxide layer that improves conductivity.
    3. C Iron is used unalloyed (as pure iron) for the bodywork of cars, because pure iron is harder and more resistant to denting than any of its alloys.
    4. D Copper is used for electrical wiring because it is an excellent conductor of electricity and can be drawn into thin, flexible wires.
15. 151 mark

    Most metal ores are the oxides of the metal, and extracting the metal from its ore always requires a chemical reduction process.

    Iron is a transition metal, extracted from iron oxide ore.

    Which statement correctly describes both this extraction and a general property of transition metals such as iron?

    1. A Extracting iron from iron oxide requires oxidation (adding oxygen, or losing electrons); transition metals, including iron, commonly form coloured compounds and can exist in more than one oxidation state.
    2. B Extracting iron from iron oxide requires reduction (removing oxygen, or gaining electrons); transition metals, including iron, commonly form coloured compounds and can exist in more than one oxidation state.
    3. C Extracting iron from iron oxide requires reduction (removing oxygen, or gaining electrons); transition metals, including iron, are always colourless in their compounds and exist in only one oxidation state.
    4. D Extracting iron from iron oxide requires neither oxidation nor reduction, since it is a simple physical separation of iron from oxygen using heat alone.

Worked solutions

Every question below carries the reasoning, not just the answer. The official material for this test publishes a correct option letter and nothing else.

1. Question 1Answer: B

   1. An electrode is a rod, often made of an inert material such as graphite, that carries current into or out of the substance being electrolysed.
   2. By definition the cathode is the negative electrode, where cations are attracted and reduced, and the anode is the positive electrode, where anions are attracted and oxidised.
   3. The electrolyte is the substance undergoing electrolysis, here molten zinc chloride, since it is the ionic compound whose ions are free to move and carry the current, not the electrode or the battery.
   4. So the correct combination is cathode = negative electrode, anode = positive electrode, electrolyte = the substance being electrolysed, which is option B.
   • Why not A: Swaps the cathode and anode: the cathode is actually the negative electrode and the anode the positive electrode, the opposite way round from this option.
   • Why not C: States the correct polarity for cathode and anode, but confuses the electrolyte with the electrode itself, describing it as a metal rod rather than the ionic substance being electrolysed.
   • Why not D: Swaps cathode and anode (giving the anode as negative and the cathode as positive) and also confuses the electrolyte with the power source, when the electrolyte is the substance undergoing electrolysis, not the battery.

2. Question 2Answer: C

   1. In electrolysis, cations must move to one electrode and be reduced there, while anions must move to the other electrode and be oxidised there, so each electrode needs a fixed, unchanging polarity throughout.
   2. A direct current supply keeps one electrode permanently negative (the cathode) and the other permanently positive (the anode), so ions are drawn consistently in one direction and can be discharged.
   3. An alternating current supply reverses which electrode is positive and negative many times each second, so ions would be pulled first one way and then the other, and no net electrolysis product would build up at either electrode.
   4. This is why electrolysis cells are always run from a dc supply, matching option C.
   • Why not A: Invents an incorrect reason based on voltage magnitude; the issue is not that dc has a higher voltage than ac, but that dc keeps each electrode's polarity fixed, which ac does not.
   • Why not B: Overstates the effect: an alternating current can still pass through an electrolyte, since ions can still move; the real problem is that with the polarity constantly reversing, no net product builds up at either electrode, not that no current flows at all.
   • Why not D: Invents a false requirement, confusing alternating current with a pulsed direct current; electrolytes do not need current delivered in pulses, they need each electrode to keep a fixed polarity.

3. Question 3Answer: B

   1. In molten lead(II) bromide the only ions present are Pb2+ (cations) and Br- (anions), free to move because the compound is molten.
   2. Cations are attracted to the negative cathode, where they gain electrons: Pb2+ + 2e- -> Pb, which is reduction, producing molten lead metal.
   3. Anions are attracted to the positive anode, where they lose electrons: 2Br- -> Br2 + 2e-, which is oxidation, producing bromine.
   4. So reduction (electron gain) always happens at the cathode and oxidation (electron loss) always happens at the anode, matching option B.
   • Why not A: Swaps the meanings of oxidation and reduction, describing the cathode process (electron gain) as if it were electron loss, and the anode process (electron loss) as if it were electron gain.
   • Why not C: Swaps which ion travels to which electrode, sending the anion (Br-) to the cathode and the cation (Pb2+) to the anode, when cations are attracted to the negative cathode and anions to the positive anode.
   • Why not D: Correctly reduces Pb2+ at the cathode, but wrongly describes the anode process as reduction too, forgetting that oxidation (electron loss) must occur at the anode.

4. Question 4Answer: A

   1. In aqueous copper(II) sulfate, both Cu2+ and H+ ions (the latter from the water) are present and are attracted to the negative cathode.
   2. When more than one type of cation is available, the ion of the less reactive element is discharged preferentially; copper is less reactive than hydrogen, so Cu2+ ions are reduced instead of H+ ions.
   3. The correct half-equation shows Cu2+ gaining two electrons to form copper atoms: Cu2+ + 2e- -> Cu.
   4. This is reduction (electron gain) at the cathode, matching option A, and it is why a pink-brown deposit of copper builds up on the cathode rather than bubbles of hydrogen gas.
   • Why not B: Shows copper being formed from Cu2+, but places the electrons on the wrong side, as if the ions were losing electrons rather than gaining them; this is the direction for oxidation, not the reduction that happens at the cathode.
   • Why not C: Writes the reverse process entirely, showing copper metal being oxidised into Cu2+ ions; this is what happens at a copper anode, not at the inert cathode described here.
   • Why not D: Correctly balances a half-equation for hydrogen gas being discharged, which is what would happen if hydrogen ions were preferentially reduced instead of copper ions; but copper is less reactive than hydrogen, so it is Cu2+ that is discharged here, not H+.

5. Question 5Answer: A

   1. Electroplating uses electrolysis to coat an object with a thin, even layer of another metal, often to improve its appearance or to protect it from corrosion.
   2. The object to be plated (the spoon) is made the cathode, and a bar of the plating metal (silver) is made the anode, in a solution containing ions of that metal.
   3. At the cathode, silver ions gain electrons and are reduced, depositing as solid silver onto the spoon's surface: Ag+ + e- -> Ag.
   4. This can improve the spoon's appearance and help protect the steel underneath from corrosion, matching option A.
   • Why not B: Swaps which electrode the spoon is; it should be made the cathode, not the anode, so that it attracts and reduces the silver cations onto its surface.
   • Why not C: Dismisses electrolysis entirely, describing plain dip-coating in molten metal, which is not how electroplating works and ignores the electric current that drives the process.
   • Why not D: Correctly places the spoon as the cathode but wrongly says the silver ions are oxidised there; gaining electrons to deposit as solid metal is reduction, not oxidation.

6. Question 6Answer: C

   1. Propane, C3H8, is an alkane, and alkanes are a homologous series with general formula CnH2n+2; for propane n = 3, giving C3H8.
   2. Complete combustion of a hydrocarbon in plentiful oxygen converts all the carbon in it to carbon dioxide and all the hydrogen to water.
   3. Balancing atom by atom: 3 carbon atoms need 3CO2, and 8 hydrogen atoms need 4H2O; the right-hand side then has (3 x 2) + (4 x 1) = 10 oxygen atoms in total, which needs 5O2 on the left.
   4. So the balanced equation is C3H8 + 5O2 -> 3CO2 + 4H2O, matching option C.
   • Why not A: Produces carbon monoxide (CO) instead of carbon dioxide (CO2); carbon monoxide is a product of incomplete combustion, not complete combustion.
   • Why not B: Uses too few oxygen molecules; 3O2 supplies only 6 oxygen atoms, which cannot provide the 10 oxygen atoms needed to form 3CO2 + 4H2O, so the equation does not balance.
   • Why not D: Keeps all the carbon as CO2 but wrongly leaves the hydrogen as H2 gas rather than combining it with oxygen to form water, when combustion of a hydrocarbon converts its hydrogen into water.

7. Question 7Answer: A

   1. But-2-ene is an alkene, a homologous series with general formula CnH2n, containing a C=C double bond, here between the second and third carbons of a four-carbon chain.
   2. The C=C double bond is the reactive part of an alkene: it can open up in an addition reaction, with each carbon of the former double bond forming a new single bond to one bromine atom.
   3. This converts the orange bromine molecule into a colourless dibromoalkane, so the bromine water decolourises; this test distinguishes an alkene (decolourises bromine water) from an alkane (stays orange, having no double bond to react).
   4. So the correct description is option A: the bromine water turns colourless because the double bond adds across the bromine molecule.
   • Why not B: Denies that alkenes react with bromine water at all, describing the behaviour of a saturated alkane instead; it misses the point of the C=C double bond as the reactive site.
   • Why not C: Correctly notes the colour change but misnames the reaction as substitution (replacing a hydrogen atom); the actual reaction is addition, where the double bond opens and both carbon atoms bond to a bromine atom each.
   • Why not D: Invents an incorrect colour and an incorrect blue complex, which has no basis in this reaction; the observed colour change is orange to colourless, not to blue.

8. Question 8Answer: C

   1. Cracking breaks a long-chain (saturated) alkane into shorter alkane and alkene molecules using heat and a catalyst, and the total numbers of carbon and hydrogen atoms are conserved across the reaction.
   2. The starting molecule, C16H34, has 16 carbon atoms and 34 hydrogen atoms in total.
   3. One product is given as octane, C8H18 (8 carbons, 18 hydrogens); the other product must therefore have 16 - 8 = 8 carbons and 34 - 18 = 16 hydrogens, giving the formula C8H16.
   4. C8H16 fits the alkene general formula CnH2n (n = 8), as expected, since cracking a saturated alkane into two saturated alkanes is impossible without an unsaturated (alkene) product to absorb the hydrogens left over, so the balanced equation is C16H34 -> C8H18 + C8H16, option C.
   • Why not A: Gives two identical alkane molecules (C8H18 + C8H18, C16H36 overall), which has two more hydrogen atoms than the C16H34 starting material provides; splitting a saturated alkane into two smaller alkanes without producing an alkene is not possible without adding extra hydrogen from somewhere.
   • Why not B: Gives a second product, C8H14, with too few hydrogen atoms overall (18 + 14 = 32, not 34), an arithmetic slip in working out how many hydrogen atoms remain for the second fragment.
   • Why not D: Splits the molecule into two fragments of formula C8H17, which cannot be a stable neutral hydrocarbon (an odd number of hydrogens on 8 carbons does not correspond to any real alkane, alkene or similar molecule), and it does not identify octane as one product as the question requires.

9. Question 9Answer: D

   1. Chloroethene, CH2=CHCl, is an unsaturated monomer, since it contains a C=C double bond.
   2. In addition polymerisation, the C=C double bond in each monomer opens up, and every monomer joins to the next by new single carbon-carbon bonds; no atoms are lost, so every atom present in the monomer, including the chlorine, appears in the repeating unit.
   3. The repeating unit is therefore -CH2-CHCl-, repeated many times to form the long-chain polymer, poly(chloroethene), more commonly known as PVC.
   4. So the correct repeating unit is [-CH2-CHCl-]n, matching option D.
   • Why not A: Assumes an elimination of HCl happens during polymerisation, rather than the simple addition where the C=C double bond opens and every atom of the monomer, including the chlorine, is retained in the polymer.
   • Why not B: Doubles up the chlorine atom incorrectly; each monomer unit, CH2=CHCl, contributes exactly one chlorine atom to the repeating unit, not two.
   • Why not C: Confuses addition polymerisation with condensation polymerisation, wrongly introducing a water by-product, which is characteristic of forming polyesters, polyamides or proteins, not the addition polymerisation of an alkene-based monomer.

10. Question 10Answer: C

    1. Condensation polymerisation joins monomers that each carry two reactive groups, with a small molecule released every time a new bond forms between them, unlike addition polymerisation where no atoms are lost.
    2. Amino acids each carry an amine group and a carboxylic acid group; when two amino acids react, the reactive groups combine to form a new bond (a peptide link) with the loss of one water molecule per bond.
    3. Repeating this joining of many amino acid molecules produces a long chain called a polypeptide, and one or more polypeptide chains folded together form a protein.
    4. So the correct description is option C: each new bond is formed with the loss of a water molecule, giving a polypeptide (protein) chain.
    • Why not A: Names the wrong small molecule lost (hydrogen gas rather than water) and wrongly reclassifies the polymer as an addition polymer; a small molecule being released at each joint is the defining feature of a condensation polymer, not an addition one.
    • Why not B: Describes addition polymerisation, where no atoms are lost, rather than condensation polymerisation; this misses the defining difference the question itself states, that a small molecule is released at each new bond.
    • Why not D: Names the wrong small molecule lost (carbon dioxide rather than water), a plausible-sounding but incorrect by-product for this reaction.

11. Question 11Answer: B

    1. Alcohols form a homologous series with general formula CnH2n+1OH, one more hydrogen atom than the corresponding alkene of the same carbon chain length, because the -OH group replaces one hydrogen on an otherwise saturated chain.
    2. Propan-1-ol, C3H7OH, reacts with reactive metals such as sodium in a similar way to water reacting with sodium, though less vigorously.
    3. Sodium displaces the hydrogen atom from the -OH group, producing sodium propoxide and hydrogen gas, seen as bubbles, which can be tested with a lit splint to give a characteristic squeaky pop.
    4. So the correct description is option B: general formula CnH2n+1OH, with hydrogen gas produced when sodium reacts with the alcohol.
    • Why not A: Gives the general formula for an alkane (CnH2n+2) rather than for an alcohol, and also names the wrong gas produced, oxygen instead of hydrogen.
    • Why not C: Has the correct general formula but wrongly denies that sodium reacts with alcohols; sodium is reactive enough to displace hydrogen from the -OH group, even though alcohols are only very weakly acidic.
    • Why not D: Uses the alkene general formula, CnH2n, with OH simply appended, rather than the alcohols' own general formula CnH2n+1OH, so it is one hydrogen atom short; it also names the wrong gas produced, carbon dioxide instead of hydrogen.

12. Question 12Answer: B

    1. Carboxylic acids, such as ethanoic acid, are a homologous series with general formula CnH2n+1COOH, and they behave as weak acids: they only partially ionise in water, unlike strong acids such as hydrochloric acid, which fully ionise.
    2. When a carboxylic acid reacts with an alcohol in the presence of an acid catalyst, here concentrated sulfuric acid, an esterification reaction takes place.
    3. Ethanoic acid, CH3COOH, reacts with ethanol, C2H5OH, to form the ester ethyl ethanoate, CH3COOC2H5, and water.
    4. So the correct description is option B: carboxylic acids are weak acids, and this reaction produces an ester and water.
    • Why not A: Correctly identifies the ester product but wrongly calls carboxylic acids strong acids that fully ionise in water; carboxylic acids such as ethanoic acid are in fact weak acids that only partially ionise.
    • Why not C: Correctly notes that carboxylic acids are weak but wrongly describes the reaction with an alcohol as though it were the reaction of an acid with a reactive metal, producing a salt and hydrogen gas; that is not what happens between a carboxylic acid and an alcohol.
    • Why not D: Correctly notes that carboxylic acids are weak but invents an incorrect pair of products, an alcohol and carbon dioxide, rather than the true products, an ester and water.

13. Question 13Answer: C

    1. In a displacement reaction, a more reactive metal displaces a less reactive metal from a solution of its salt, because the more reactive metal forms positive ions more readily and takes the less reactive metal's place.
    2. X displaces both Y and Z, so X is more reactive than both. Y displaces Z but is itself displaced by X (Y cannot displace X), so Y is more reactive than Z but less reactive than X. Z displaces neither, so Z is the least reactive of the three.
    3. This gives the reactivity order, most to least reactive: X, Y, Z.
    4. Reactivity is linked to how easily a metal forms positive ions: the most reactive metal, X, loses electrons to form its positive ions most easily, which is why it can displace the less reactive Y and Z from their salt solutions, matching option C.
    • Why not A: Reverses the reactivity order entirely, treating the metal that displaces nothing (Z) as the most reactive, when a metal that cannot displace either of the others must in fact be the least reactive.
    • Why not B: Gets the reactivity order right (X, Y, Z) but reverses the definition, claiming the most reactive metal forms its ions least easily, when reactivity is in fact linked to forming positive ions most easily.
    • Why not D: Gets the order wrong by placing Y ahead of X; since Y cannot displace X, X must be more reactive than Y, not the other way around.

14. Question 14Answer: D

    1. A metal's uses are chosen to match its physical and chemical properties, such as high electrical conductivity, low reactivity (resistance to corrosion), or a useful balance of strength and low density.
    2. Copper is an excellent conductor of electricity and is easily drawn into wires, which is exactly why it is the standard choice for electrical wiring.
    3. Other genuine examples include aluminium's low density making it useful for overhead cables, gold's very low reactivity making it useful for electrical contacts that must not corrode, and alloys such as steel being harder than pure iron, making them more suitable than pure iron for car bodywork.
    4. So the statement that correctly matches a property to a use is option D: copper's high conductivity is why it is used for electrical wiring.
    • Why not A: Reverses a real property: aluminium is in fact less dense than copper, which is the genuinely relevant property for keeping overhead cables light, not denser as this option claims.
    • Why not B: Reverses a real property: gold is used in electrical connectors precisely because it is highly unreactive, so contacts stay clean and conductive, not because it is reactive as this option claims.
    • Why not C: Reverses a real property: alloys such as steel are used for car bodywork because alloying pure iron with carbon and other elements makes it harder and stronger than pure (unalloyed) iron, which is comparatively soft.

15. Question 15Answer: B

    1. Most metal ores are oxides of the metal, so extracting the free metal from its ore means removing the oxygen that is chemically bonded to it, which is a reduction process, in terms of oxygen loss or in terms of the metal ions gaining electrons.
    2. Iron is extracted from iron oxide by reduction, for example using carbon or carbon monoxide as the reducing agent in a blast furnace.
    3. Iron is also a transition metal, and transition metals share several common properties: they can exist as stable ions in more than one oxidation state, they often form coloured compounds, and they are often useful as catalysts.
    4. So the correct statement is option B: extraction is by reduction, and transition metals commonly form coloured compounds with more than one oxidation state.
    • Why not A: Correctly describes transition metal properties but wrongly calls the extraction an oxidation process; converting an oxide ore into the free metal means removing oxygen (or adding electrons), which is reduction, not oxidation.
    • Why not C: Correctly identifies reduction but wrongly claims transition metal compounds are always colourless and exist in only one oxidation state, when transition metals are in fact characterised by forming coloured compounds and multiple oxidation states.
    • Why not D: Wrongly denies that a redox process is involved at all; converting an oxide ore into the free metal is a chemical reduction, not a purely physical separation by heat.