Metals

• If you can say where a metal sits relative to carbon and relative to hydrogen, you can already predict its acid reaction, its displacement behaviour, whether it can protect iron, and how it is extracted. Those two reference points do more work than any other fact in this chapter.
• Eleven danger zones, one habit that defuses most of them: before writing a sentence about a metal, say silently where it sits relative to carbon, relative to hydrogen, and relative to iron. Those three comparisons decide extraction, acid reaction and protection respectively.
• Optional mnemonic, if you want one: Kings Name Castles Magnificent, Always Calling Zinc Fearless; Heroes Cut Against Authority. Use it only as a scaffold — the chunk meanings above are what you actually reason with.
• Recite the chain, not the list: coke burns → heat and carbon dioxide → carbon dioxide over hot coke → carbon monoxide → carbon monoxide reduces the ore → molten iron → and separately, limestone decomposes → calcium oxide → calcium oxide takes the sand → slag.
• If you only revise one of these eight, revise number 6. Barrier versus sacrificial is the single distinction that appears in the most different question types — multiple choice, short explanation, extended reasoning and the applied “choose a method” question.
• Thirty-eight examples, one route: evidence → position or rule → equation or method → observation or role → audit → answer. If a question ever leaves you stuck, write down what you have been given and turn it into a comparison. That single move unlocks most of Topic 9.

• Compare the thermal conductivity of metals and non-metals.
• Compare the electrical conductivity of metals and non-metals.
• Compare malleability and ductility in metals with the brittleness of most solid non-metals.
• Compare typical melting and boiling points of metals and non-metals.
• Compare a pure metal with an alloy at particle level.
• Describe the general reactions of metals with dilute acids, with cold water and steam, and with oxygen.
• Describe the uses of aluminium in aircraft, in overhead electrical cables and in food containers, and of copper in electrical wiring.
• Describe the composition of brass and of stainless steel, and one use of stainless steel.
• State the order of the reactivity series from potassium to gold, including carbon and hydrogen.
• Describe the conditions required for rusting and name the product.
• Describe barrier methods of rust prevention and galvanising.
• Describe the extraction of iron in the blast furnace and of aluminium by electrolysis.
• Explain the order of the reactivity series in terms of the tendency of an atom to form a positive ion.
• Explain displacement of one metal from an aqueous solution of its ions by a more reactive metal.
• Explain why the reactions of metals with cold water, steam and dilute acid follow their positions in the series.
• Explain why aluminium appears less reactive than it is, using its oxide layer.
• Explain why an alloy is harder than the pure metal, using layers of different-sized particles.
• Explain sacrificial protection in terms of relative reactivity and preferential electron loss.
• Explain why ease of extraction is related to position in the reactivity series.
• Explain the role of cryolite and why the carbon anodes are replaced.
• Deduce an order of reactivity from a set of unfamiliar experimental results, and say where the evidence runs out.
• Identify a pure metal or an alloy from a particle diagram, and say what the evidence was.
• Write balanced symbol equations, ionic equations and electrode half-equations for the reactions in this topic.
• Choose a protection method for a stated object in a stated environment, and justify it.

Why this matters. This is the one process in Topic 9 where the electrode signs, the ion movements and the electron counts all have to be right at once. Every part of it is examinable, and each part is a separate mark.

Reactivity Series

An order of metals arranged by how readily each one loses electrons to form a positive ion, with the most reactive at the top. Carbon and hydrogen are included as non-metal reference points: carbon marks the boundary for extraction method and hydrogen marks the boundary for reaction with dilute acids.

Malleability

The property of a material that allows it to be hammered, rolled or pressed into a new shape without breaking. In metals it arises because layers of identical positive ions can slide over one another while the delocalised electrons keep holding the structure together.

Displacement Reaction

A reaction in which a more reactive metal takes the place of a less reactive metal in a solution of that metal's ions. The more reactive metal loses electrons and goes into solution as ions, while the ions of the less reactive metal gain those electrons and are deposited as the solid metal.

Ductility

The property of a material that allows it to be drawn out into a thin wire without snapping. In metals it has the same structural cause as malleability: layers of identical positive ions slide past one another while the delocalised electrons continue to bond the structure.

Density

The mass of a material per unit volume. A low-density material gives a large object for a small mass, which is why aluminium rather than a denser metal is chosen for aircraft bodies and for overhead cables that must not sag under their own weight.

Stainless Steel

An alloy of iron with elements such as chromium, nickel and carbon. The different-sized particles disrupt the regular layers of iron so the layers cannot slide easily, making it hard and strong, and the chromium gives it resistance to rusting, which together make it the standard material for cutlery and surgical instruments.

Metal Oxide

A compound formed when a metal combines with oxygen. Metal oxides are generally basic, and most metals occur in the Earth as their oxides or as other compounds, which is why they must be extracted rather than dug up as the element.

Sacrificial Protection

A method of preventing rust in which a more reactive metal is attached to iron or steel and is corroded in its place. The more reactive metal loses electrons in preference to the iron, so the iron does not form ions and does not rust; the attached metal is gradually eaten away and is replaced.

Protective Oxide Layer

A thin, tough, continuous layer of aluminium oxide that forms on the surface of aluminium in air. It sticks firmly to the metal and keeps air, water and acids away from it, so the metal beneath appears unreactive even though aluminium is high in the reactivity series.

Metal Hydroxide

The compound formed when a reactive metal reacts with cold water, alongside hydrogen gas. A soluble metal hydroxide gives an alkaline solution, which is why universal indicator turns purple when potassium, sodium or calcium reacts with water.

Rusting

The corrosion of iron and steel, which happens only when both oxygen and water are present and produces hydrated iron(III) oxide. Salt speeds rusting up but is not one of the required conditions, and the word rust applies to iron and steel alone, not to the corrosion of other metals.

Alloy

A mixture of a metal with one or more other elements. The components keep their own identities and there is no fixed formula, because no chemical reaction has taken place; metallic bonding still holds the structure together, which is why an alloy is still a metal in its behaviour.

Salt

The compound formed when the hydrogen of an acid is replaced by a metal. When a metal above hydrogen in the reactivity series reacts with dilute hydrochloric acid the salt is a chloride, and hydrogen gas is released at the same time.

Galvanising

Coating iron or steel with a layer of zinc. The zinc acts as a barrier that keeps oxygen and water away from the iron, and because zinc is more reactive than iron it also acts sacrificially, so the iron is still protected at any point where the coating is scratched.

Barrier Protection

A method of preventing rust by covering iron or steel with a layer that keeps oxygen and water away from the metal surface. Painting, greasing and coating with plastic all work this way, and all of them stop working at any point where the layer is broken.

Corrosion Resistance

The ability of a metal to stay unattacked in air, water or food acids. Aluminium has it not because it is unreactive but because a thin, tough, continuous layer of aluminium oxide forms on its surface and keeps air and water away from the metal underneath.

Metal Ore

A rock containing enough of a metal compound to make extraction of the metal worthwhile. Most metals occur combined with oxygen or other elements rather than as the element itself, and how tightly the metal holds on to that combination is set by its position in the reactivity series.

Metal

An element whose atoms are held in a giant lattice of positive ions surrounded by delocalised electrons. Metals are generally good conductors of heat and electricity, malleable and ductile, and have high melting and boiling points; chemically they tend to lose electrons and form positive ions.

Aluminium Electrolysis

The extraction of aluminium by passing electricity through purified aluminium oxide dissolved in molten cryolite. Aluminium ions gain electrons at the negative cathode to form molten aluminium, oxide ions lose electrons at the positive carbon anodes to form oxygen, and that oxygen burns the anodes away so they must be replaced.

Blast Furnace

The tall furnace in which iron is extracted from its ore. Hematite, coke and limestone are fed in at the top and hot air is blasted in at the bottom; carbon monoxide formed from the coke reduces the iron(III) oxide to molten iron, while calcium oxide from the limestone removes sandy impurities as molten slag.

• 1. “All metals have high melting points and all non-metals are insulators.” Repair The comparison is general, not universal. Mercury is a liquid at room temperature; graphite is a non-metal that conducts electricity. Write “metals generally have higher melting points” and the mark is safe. Where Lesson 9.1A.
• 2. “Malleable means it can be drawn into wires.” Repair Malleable = can be hammered or pressed into shape. Ductile = can be drawn out into a wire. Copper wiring needs ductility; aluminium foil needs malleability. Swapping them is a straight lost mark. Where Lesson 9.1A.
• 3. “An alloy is a compound of two metals.” Repair An alloy is a mixture of a metal with other elements. There is no fixed formula, no chemical reaction has happened, and the metallic bonding is still there. Also note “other elements”, not “other metals” — carbon in steel is not a metal. Where Lesson 9.3A.
• 4. “Copper displaces iron from iron(II) sulfate.” Repair Displacement only runs downhill: the more reactive metal takes the place of the less reactive one. Copper is below iron, so nothing happens. Check the direction before you write an equation, every time. Where Lesson 9.4B.
• 5. “Carbon and hydrogen are in the series, so they must be metals.” Repair They are non-metal reference points. Carbon sits between aluminium and zinc and marks the boundary between electrolysis and reduction. Hydrogen sits between iron and copper and marks the boundary for reaction with dilute acid. Get their positions wrong and two whole subtopics collapse. Where Lesson 9.4A.
• 6. “Aluminium does not react with water, so it must be low in the reactivity series.” Repair Aluminium is high in the series, above zinc and iron. It behaves as though it were unreactive because a thin, tough, continuous layer of aluminium oxide forms on the surface and stops air and water reaching the metal. Say “oxide layer”, never “low reactivity”. Where Lesson 9.4E.
• 7. “Iron needs oxygen, water and salt to rust.” Repair The two required conditions are oxygen and water. Salt speeds rusting up but is not necessary — a nail rusts perfectly well in pure water and air. Listing salt as a condition is a common and expensive slip. Where Lesson 9.5A.
• 8. “Any metal coating protects the iron underneath, even when scratched.” Repair Only a more reactive coating keeps protecting after a scratch, because it loses electrons in preference to the iron. Zinc does; tin does not. A tin coating is a barrier only, and a scratched tin can rusts faster than bare iron. Where Lessons 9.5B and 9.5C.
• 9. “Coke reduces the iron(III) oxide in the blast furnace.” Repair In the route you are required to give, the reducing agent is carbon monoxide: \(\mathrm{Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2}\). The coke does two other jobs — it burns to release heat and carbon dioxide, and it then converts that carbon dioxide into the carbon monoxide that does the reducing. Where Lesson 9.6B.
• 10. “Cryolite is a catalyst.” Repair It is a solvent for the aluminium oxide. Dissolving the oxide in molten cryolite lets the cell run at a much lower temperature than molten aluminium oxide alone would need, so less energy is used. A catalyst changes the rate of a reaction; cryolite changes what the electrolyte is. Where Lesson 9.6C.
• 11. “The anode is negative because it attracts positive ions.” Repair In electrolysis the cathode is negative and attracts the positive \(\mathrm{Al^{3+}}\) ions; the anode is positive and attracts the negative \(\mathrm{O^{2-}}\) ions. Electrons are gained at the cathode and lost at the anode. Getting the signs backwards turns two correct half-equations into zero marks. Where Lesson 9.6C.
• 1. “The limestone reduces the iron(III) oxide.” Defect Limestone is nowhere near the reduction. It decomposes to calcium oxide and then removes the silica. Reason Reduction means removing oxygen. Limestone gives off carbon dioxide; it does not take oxygen from anything. Repair “Carbon monoxide reduces the iron(III) oxide. Limestone removes the silica impurity as slag.” Transfer If no limestone were added, what would still work and what would fail? Answer: the iron would still be reduced, but the silica would stay in it as an impurity.
• 2. “Coke acts as a catalyst.” Defect A catalyst is not used up and is not a reactant. Coke is consumed continuously and must be fed in constantly. Reason Coke appears as a reactant in two of the five equations, steps 1 and 2. Anything that appears in the equation and disappears from the furnace is a reactant. Repair “Coke is a fuel and the source of the reducing agent.” Transfer Name one substance in the furnace that is essentially unchanged. Answer: the nitrogen in the air blast, which passes through and leaves in the waste gases.
• 3. “Carbon dioxide reduces the iron(III) oxide.” Defect Carbon dioxide is a product of the reduction, not the agent of it. Reason Carbon dioxide is already fully combined with oxygen, so it has no appetite for more. Carbon monoxide has room to take one more oxygen, which is exactly what it does. Repair \(\mathrm{Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2}\) — carbon monoxide in, carbon dioxide out. Transfer Which step turns carbon dioxide back into a reducing agent? Answer: step 2, \(\mathrm{CO_2 + C \rightarrow 2CO}\), so the furnace recycles it.
• 4. “Slag is the waste iron that did not melt properly.” Defect Slag contains no iron. It is calcium silicate, formed from the limestone and the sandy impurity. Reason If slag were unmelted iron the process would be losing most of its product, and there would be no reason to add limestone at all. Repair “Slag is molten calcium silicate, \(\mathrm{CaSiO_3}\), formed when calcium oxide reacts with silica. It floats on the iron and is tapped off separately.” Transfer Why does slag float? Answer: it is less dense than molten iron.
• 5. “Calcium oxide is one of the raw materials charged into the furnace.” Defect Calcium oxide is made inside the furnace. The raw material is calcium carbonate — limestone. Reason Step 4 exists precisely to produce the calcium oxide. If it were charged directly, step 4 would be pointless. Repair Name the three charged solids as hematite, coke and limestone. Calcium oxide is an intermediate. Transfer Name the other substance produced in step 4. Answer: carbon dioxide, which step 2 can convert into more carbon monoxide.
• 6. “\(\mathrm{Fe_2O_3 + CO \rightarrow Fe + CO_2}\)” Defect Not balanced. Fe: 2 on the left, 1 on the right. O: \(3 + 1 = 4\) on the left, 2 on the right. Reason A correct-looking equation with the right species still scores zero if the numbers do not match. Balance is checked separately from chemistry. Repair \(\mathrm{Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2}\). Fe 2 = 2, C 3 = 3, O 6 = 6. Transfer Balance the equation for the reduction of copper(II) oxide by carbon monoxide. Answer: \(\mathrm{CuO + CO \rightarrow Cu + CO_2}\); Cu 1 = 1, C 1 = 1, O 2 = 2 — already balanced as written.
• 1. “All metals have high melting points and all non-metals are gases.” Defect Two universal claims where the syllabus makes general ones. Reason Mercury is a metal that is liquid at room temperature; sulfur and iodine are solid non-metals. One counter-example destroys a universal claim. Repair “Metals generally have higher melting points than non-metals.” Transfer Name a metal that breaks the pattern and a non-metal that breaks it. Mercury; diamond.
• 2. “Copper is malleable, which is why it is drawn into wires.” Defect The wrong one of the two words. Reason Malleable = hammered or pressed into shape. Ductile = drawn into a wire. Wires need ductility. Repair “Copper is ductile, so it can be drawn into thin wires.” Transfer Which word applies to aluminium cooking foil? Malleable — foil is rolled into a sheet.
• 3. “Non-metals never conduct electricity.” Defect Universal claim again, and this one has a famous exception. Reason Graphite is a non-metal with delocalised electrons between its layers, so it conducts. Repair “Non-metals are generally insulators; graphite is the exception.” Transfer Why does graphite conduct when diamond does not? Graphite has electrons that are free to move; in diamond every electron is held in a bond.
• 4. “An alloy is a compound formed when two metals are melted together.” Defect Calls a mixture a compound. Reason No reaction occurs; there is no fixed formula, and the proportions can be varied while it remains the same alloy. Repair “An alloy is a mixture of a metal with other elements.” Transfer Give one piece of evidence that brass is a mixture. Its composition can be varied; the copper and zinc are not chemically bonded.
• 5. “An alloy is a mixture of two metals.” Defect Too narrow — and it makes stainless steel impossible to describe. Reason Carbon in stainless steel is a non-metal, and it is still part of the alloy. Repair “A mixture of a metal with one or more other elements.” Transfer Name the elements in stainless steel. Iron, with chromium, nickel and carbon.
• 6. “Alloys are harder because the smaller atoms fill the gaps between the big ones.” Defect Invents a mechanism the syllabus does not use, and it is not what the diagram shows. Reason The credited mechanism is about layers, not gaps: differently sized particles disrupt the regular layers. Repair “Different-sized particles disrupt the regular layers, so the layers cannot slide over each other easily.” Transfer Does an alloy have to contain smaller particles? No — larger ones disrupt the layers just as well.
• 7. “This diagram shows an alloy because the circles are two different colours.” Defect Uses a drawing convention as physical evidence. Reason Colour is chosen by whoever drew the diagram. Size, or a key naming a second element, is what tells you. Repair “The particles are of different sizes, so this is an alloy.” Transfer A diagram has equal circles in two shades, no key. What can you conclude? Nothing about alloying — the evidence does not support a conclusion either way.
• 8. “Aluminium is used for drinks cans because it is unreactive.” Defect Contradicts subtopic 9.4, where aluminium is above zinc and iron. Reason It resists corrosion because of the oxide layer, which is a surface effect, not a low position. Repair “Aluminium resists corrosion because a tough oxide layer forms on its surface.” Transfer What happens to aluminium if that layer is removed? It reacts as its high position predicts, until a new layer forms.
• 9. “Overhead cables should be copper, because copper is the better conductor.” Defect Optimises the wrong property for the situation. Reason The cable also has to hold itself up over a long span. Aluminium’s low density is what makes that possible. Repair “Aluminium is used, because it has a low density and is a good conductor.” Transfer Why is copper right for house wiring? A short wire inside a wall does not have to support itself, so the better conductivity wins.
• 10. “Carbon and hydrogen are the least reactive metals in the series.” Defect Calls two non-metals metals, and misplaces both. Reason They are reference points. Carbon sits between aluminium and zinc; hydrogen between iron and copper. Repair “Carbon and hydrogen are non-metals included as reference points.” Transfer What does each marker predict? Carbon: the extraction method. Hydrogen: whether the metal reacts with a dilute acid.
• 11. “\(\mathrm{Cu(s) + FeSO_4(aq) \rightarrow CuSO_4(aq) + Fe(s)}\)” Defect Displacement written in the wrong direction. Reason Copper is below iron, so it cannot lose electrons to iron(II) ions. Repair “No reaction, because copper is less reactive than iron.” Transfer Which way round does it work? \(\mathrm{Fe(s) + Cu^{2+}(aq) \rightarrow Fe^{2+}(aq) + Cu(s)}\).
• 12. “\(\mathrm{Zn(s) + Ag^+(aq) \rightarrow Zn^{2+}(aq) + Ag(s)}\)” Defect The chemistry is right but the charges do not balance: \(-1\) net difference between the sides. Reason A zinc atom releases two electrons, but a single silver ion accepts only one. Repair \(\mathrm{Zn(s) + 2Ag^+(aq) \rightarrow Zn^{2+}(aq) + 2Ag(s)}\). Charge: \(+2\) on both sides. Transfer Balance copper with silver ions. \(\mathrm{Cu(s) + 2Ag^+(aq) \rightarrow Cu^{2+}(aq) + 2Ag(s)}\).
• 13. “Magnesium reacts with steam to give magnesium hydroxide and hydrogen.” Defect The cold-water product used for the steam reaction. Reason A hydroxide needs liquid water. With steam the product is the oxide. Repair \(\mathrm{Mg(s) + H_2O(g) \rightarrow MgO(s) + H_2(g)}\). Transfer Which state symbol on the water tells the examiner you knew? \(\mathrm{(g)}\).
• 14. “\(\mathrm{Fe + 3HCl \rightarrow FeCl_3 + H_2}\)” Defect Wrong oxidation state, and unbalanced hydrogen as well. Reason Iron with a dilute acid gives iron(II). And three hydrogens on the left cannot form one \(\mathrm{H_2}\). Repair \(\mathrm{Fe(s) + 2HCl(aq) \rightarrow FeCl_2(aq) + H_2(g)}\). Transfer What colour is the solution formed? Pale green, from \(\mathrm{Fe^{2+}(aq)}\).
• 15. “Copper does not react with dilute acid because it has a protective oxide layer.” Defect Borrows aluminium’s explanation for a metal that does not need one. Reason Copper genuinely is unreactive towards dilute acid, because it sits below hydrogen. No barrier is involved. Repair “Copper is below hydrogen in the reactivity series, so it cannot displace hydrogen from the acid.” Transfer Which metal does need the oxide-layer explanation, and why? Aluminium — because its position predicts a reaction that is not observed.
• 16. “Iron rusts when oxygen, water and salt are present.” Defect Promotes a rate factor to a required condition. Reason A nail in ordinary water and air rusts perfectly well, so salt cannot be necessary. Repair “Oxygen and water are required. Salt increases the rate.” Transfer Which tube in the four-tube experiment proves salt is not required? Tube A — it rusted without any.
• 17. “Rust is iron oxide, \(\mathrm{Fe_2O_3}\).” Defect Two pieces missing: the oxidation state and the water. Reason Iron forms more than one oxide, so the state must be given; and rust is hydrated, which is why water is one of the conditions. Repair “Hydrated iron(III) oxide, \(\mathrm{Fe_2O_3{\cdot}xH_2O}\).” Transfer Why does the formula contain \(x\)? The amount of water in rust is variable, not fixed.
• 18. “The aluminium window frames have rusted.” Defect Uses “rust” for a metal that cannot rust. Reason Rusting is specific to iron and steel. Other metals corrode. Repair “The aluminium has corroded” — and in fact aluminium resists corrosion because of its oxide layer. Transfer Name two other metals that corrode without rusting. Copper, which goes green; silver, which tarnishes.
• 19. “A scratched tin can is still protected, because tin is a metal coating.” Defect Assumes any metal coating is sacrificial. Reason Tin is below iron, so once the coating is broken the iron loses electrons in preference to the tin. The can rusts faster than bare steel would. Repair “Tin is a barrier only. Only a coating more reactive than iron protects after damage.” Transfer Which coating would still protect? Zinc — it is above iron.
• 20. “Sacrificial protection works because the zinc covers the iron and keeps water off it.” Defect Describes the barrier mechanism and calls it sacrificial. Reason A zinc block bolted to a ship’s hull covers almost none of it, yet still protects. Covering is not the mechanism. Repair “Zinc is more reactive than iron, so it loses electrons in preference to the iron, and the iron is not oxidised.” Transfer What must be true of the connection between the two metals? They must remain in contact, so electrons can pass.
• 21. “The coke reduces the iron(III) oxide in the blast furnace.” Defect Names the wrong reducing agent for the required route. Reason The coke burns to carbon dioxide and then converts it to carbon monoxide; it is the carbon monoxide that reduces the ore. Repair \(\mathrm{Fe_2O_3 + 3CO \rightarrow 2Fe + 3CO_2}\), with coke named as the fuel and the source of the carbon monoxide. Transfer Which equation makes the reducing agent? \(\mathrm{CO_2 + C \rightarrow 2CO}\).
• 22. “Cryolite is a catalyst that speeds up the electrolysis.” Defect Assigns a role the substance does not have. Reason Cryolite is the solvent. Its effect is on the temperature the electrolyte melts at, not on a reaction rate. Repair “Cryolite dissolves the aluminium oxide so the cell runs at a much lower temperature, saving energy.” Transfer Why does that matter industrially? Less energy is needed to keep the electrolyte molten, so the process costs less.
• 23. “The anode is negative because the negative ions go there.” Defect Reasons backwards from the ions to the sign. Reason The anode is positive, which is precisely why negative ions are attracted to it. Opposite charges attract. Repair “The anode is positive and attracts the negative oxide ions; the cathode is negative and attracts the positive aluminium ions.” Transfer On which side of the anode half-equation do the electrons go? The right — they are lost.
• 24. “Carbon dioxide is produced at the anode in the aluminium cell.” Defect Confuses the electrode product with what happens to it next. Reason Electrolysis discharges the ions present. The only negative ion is the oxide ion, so the product is oxygen. Repair “Oxygen is produced at the anode. It then reacts with the hot carbon anodes to form carbon dioxide.” Transfer What is the practical consequence? The anodes are burnt away and must be replaced.

• Where these six land. Checks 1 and 2 carry the whole of 9.4. Check 3 carries every equation in 9.1, 9.4 and 9.6. Checks 4 and 5 are Paper 4 marks. Check 6 is the 9.3 diagram question that appears almost every session.
• The single most common structural mistake. Students answer explain questions with observations and describe questions with theory. If the question gives you an experiment, start with what is seen. If the question gives you a position in the series, start with electrons.
• Two-mark structure. “Aluminium is used for aircraft because it has a low density” is one mark. Adding “so the aircraft has a smaller mass and uses less fuel” is the second. The property alone is never the whole answer.
• Why silver needs a 2. A silver ion carries only one positive charge, so it takes only one electron. A magnesium, zinc, iron or copper atom releases two. Two silver ions are therefore needed to accept them — hence \(\mathrm{2Ag^+}\) and \(\mathrm{2Ag}\). Check the charge on both sides every time: in \(\mathrm{Cu(s) + 2Ag^+(aq) \rightarrow Cu^{2+}(aq) + 2Ag(s)}\), the left side is \(2+\) and so is the right.
• How to write a no-reaction answer. “Nothing happens” scores nothing. “No reaction, because copper is below hydrogen in the reactivity series, so it cannot displace hydrogen from the acid” scores the marks. The reason is the answer; the observation is only the evidence.
• The naming mark. Rust is hydrated iron(III) oxide. Writing “iron oxide” misses the oxidation state; writing \(\mathrm{Fe_2O_3}\) alone misses the water. The full answer is the name plus \(\mathrm{Fe_2O_3{\cdot}xH_2O}\).
• The most valuable single sentence in 9.6B. “The reducing agent is carbon monoxide.” Coke is the source of it and the source of the heat, but coke is not what takes the oxygen off the iron(III) oxide in the route you are required to give.
• How to use these again. On a second pass, cover the answers and time yourself: 88 prompts should take about 25 minutes once the topic is solid. Mark only the ones you got completely right; a half-remembered equation is a wrong answer in an exam.
• Marking yourself honestly. If you wrote “because zinc is more reactive” but did not say so it loses electrons in preference to the iron, that is one mark, not two. The second half of every explanation is where most of Topic 9’s marks live.
• If a session goes badly. Do not restart the chapter. Identify which check failed — the mastery table gives you the code — and re-read only the lesson that owns it. Topic 9 is unusually well suited to this, because almost every failure traces back to one specific position in the reactivity series.

• Metals appears on all three papers, and it appears differently on each. Knowing which paper you are in tells you how much to write.
• Recall and one-step reasoning: the order of the series, which metal displaces which, which conditions cause rusting, which equation is balanced, which electrode is the cathode. Speed comes from having the series and the five furnace equations automatic.
• Extended explanation: justify a use from a property; explain alloy hardness with layers; explain sacrificial protection with electrons; write and balance the furnace and electrode equations; deduce an order from results. Marks come one per idea, so short separate sentences beat one long one.
• Experiment reading: the four-tube rusting investigation, displacement observations, and tables of results you must turn into an order. The examiner separates observation marks from conclusion marks, so answer both explicitly.
• The single most common structural mistake. Students answer explain questions with observations and describe questions with theory. If the question gives you an experiment, start with what is seen. If the question gives you a position in the series, start with electrons.