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S5 Chemistry: Metal Extraction (Paper 3: Challenge)
S5 Chemistry: Metal Extraction (Paper 3: Challenge)
Ten items into industrial detail: the protective oxide on aluminium and recycling, copper refining, charge calculations, ore grade and yield, and contact area in gas solid reactions, with answers.
Direct answers Answers in order: a dense oxide layer, melting takes about 5 percent of the electricity, impure anode and pure cathode, 3 mol, 1 158 000 C, 3.36 g, 0.420 t, 89.6 g, gas gives a large contact area, the oxide is insoluble and water discharges first.
01 Paper details (check answers afterwards)
| Item | Detail |
|---|---|
| Questions | 10 |
| Suggested time | 20 |
| Difficulty mix | Foundation 3 · Intermediate 3 · Challenge 3 · Error redo 1 |
| Chapter | Chapter: S5 Chemistry: Metal Extraction |
| Level | S5 |
02 Questions (10 items)
- FoundationAluminium is more reactive than iron, so why do aluminium articles resist corrosion so well?
- FoundationWhy does recycling aluminium save so much energy compared with extracting it from ore?
- FoundationIn the electrolytic refining of copper, what are the anode and the cathode made of?
- IntermediateHow many moles of electrons are needed to produce 1 mol of aluminium by electrolysis?
- IntermediateWhat quantity of charge is needed to produce 108 g of aluminium, Al = 27 and one mole of electrons is 96 500 C?
- IntermediateWhat mass of aluminium can in theory be deposited by a current of 10.0 A for 1.00 hour?
- ChallengeOne tonne of ore contains 60.0 percent iron(III) oxide. What mass of iron can be obtained in theory?
- ChallengeIf the yield is only 80.0 percent, what mass of iron is actually obtained from 160 g of iron(III) oxide?
- ChallengeWhy is carbon monoxide used in the blast furnace instead of solid carbon to reduce the ore?
- Error redoA student plans to make aluminium by electrolysing aluminium oxide solution. What is wrong?
03 Answers and one-line notes
| # | Answer | One-line note |
|---|---|---|
| 1 | A dense layer of aluminium oxide forms on the surface and prevents further oxidation of the metal beneath. | The film re-forms at once if scratched, so aluminium outlasts iron in air despite being the more reactive metal. |
| 2 | Extraction needs electrolysis of molten oxide while recycling only melts scrap metal, using about five percent of the electricity. | Electrolysis must break strong aluminium oxygen bonds repeatedly, whereas melting only overcomes weaker forces, hence the huge energy gap. |
| 3 | The anode is impure blister copper and the cathode is pure copper. | On passing current the anode dissolves as copper ions, which migrate to the cathode and deposit as high purity copper. |
| 4 | Three moles of electrons. | The aluminium ion carries three positive charges and the cathode reaction is Al3+ plus 3e- giving Al, a three to one ratio. |
| 5 | 1 158 000 C | 108 g is 4 mol of aluminium, needing 12 mol of electrons, and 12 times 96 500 gives 1 158 000 C. |
| 6 | 3.36 g | Charge is current times time, and 36 000 C is 0.373 mol of electrons, giving 0.124 mol of aluminium or 3.36 g. |
| 7 | 0.420 t | Take 60.0 percent to get 0.600 t of oxide, then multiply by the iron fraction 0.700 to obtain 0.420 t. |
| 8 | 89.6 g | The theoretical mass is 112 g, and multiplying by 0.800 gives 89.6 g. |
| 9 | Carbon monoxide is a gas and contacts the ore throughout, so the reaction is faster and more uniform. | The rate of a gas solid reaction depends on contact area; gas penetrates the pores while solid carbon touches only the surface. |
| 10 | Wrong. Aluminium oxide does not dissolve in water, and even in suspension water would be reduced first, releasing hydrogen instead of aluminium. | Aluminium must be electrolysed in the molten oxide because in water the water is discharged more readily than aluminium ions. |
04 What to do after marking
- After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
- Repeat the same item two days later; move to the next paper only when both attempts are correct.
- Parents only need the answer and note columns; there is no need to explain every item.
Redo the calculation that 10.0 A for one hour gives 3.36 g of aluminium, writing the unit at every step.Tutor Registration →
Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.