The shape of the lesson
By the end of the lesson, learners can
- Reduction by carbon: Carbon is more reactive than metals below it, so it can take the oxygen from their oxides.
- Electrolysis for reactive metals: Metals above carbon hold their oxygen too strongly for carbon to remove it.
- Ore: rock with enough metal compound to extract.
- Below carbon: reduce the oxide with carbon or CO.
- Above carbon: electrolysis of a molten compound.
- Gold, silver: found uncombined.
One picture every idea returns to
An ore is a rock that contains enough of a metal compound to make extraction worthwhile. The method of extraction depends on the metal's position in the reactivity series: metals below carbon (such as zinc, iron and copper) can be extracted by reduction of their oxides with carbon or carbon monoxide; metals above carbon (such as aluminium and sodium) must be extracted by electrolysis of a molten compound. Very unreactive metals such as gold are found uncombined.
Forty-five minutes, phase by phase
| Time | Phase | What happens in the room | Grouping |
|---|---|---|---|
| 0 to 5 min | Hook: predict | Open with the question in the title, How a metal comes out of the ground.. Most metals are found as compounds in ores, and the way to get the metal out depends on how tightly it holds on to the oxygen. Put the figure on the board: it is the one picture every idea in the lesson returns to. | Whole class, then pairs |
| 5 to 17 min | Teach and check: Reduction by carbon | Carbon is more reactive than metals below it, so it can take the oxygen from their oxides. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Electrolysis for reactive metals | Metals above carbon hold their oxygen too strongly for carbon to remove it. | Jigsaw |
| 30 to 36 min | Check | The four Stage 1 questions from the student lesson, answered on mini whiteboards or by show of fingers. Re-teach the one most get wrong. | Individual, then whole class |
| 36 to 43 min | Plenary | The exam-style questions from Stage 2, one at a time: thirty seconds alone, then a random call. The feedback lines in the key give the examiner's wording. | Individual, random call |
| 43 to 45 min | Exit and homework | Set the worksheet below (6 questions, 12 marks). Learners self-assess against the objectives before they leave. | Individual |
Protect the parts that carry the learning
The sequence carries about fifty minutes of material, so the lab is driven by one student while the class predicts rather than explored freely. Times are a guide.
Protected: the check at 30 minutes. It is the only individual read on whether the key idea landed, and it is not cut.
Cut first if the build overruns: the last check in Electrolysis for reactive metals, never the check or the plenary.
In a 60 minute block: run worksheet questions 1 to 3 in class as a Rally Coach set and model both the hardest worked example and its check live.
Jigsaw
Split the content into expert pieces. Expert groups master one piece each, then regroup so every home team has one expert per piece, and each expert teaches their piece to the team.
The full structure, with its variations and the other twelve, is on the cooperative-learning page.
What to head off, and how
| Trap learners fall into | Teaching move that pre-empts it |
|---|---|
| Aluminium is not extracted with carbon, because aluminium is above carbon in the reactivity series. | And the metal is reduced during extraction: whether by carbon or at the cathode, the metal ion gains electrons or the oxide loses oxygen. |
Extraction and the reactivity series: worksheet
6 questions, 12 marks. Written in the style of the papers; no past paper question is reproduced.
Define the term ore.
Explain why zinc can be extracted by heating zinc oxide with carbon, but aluminium cannot be extracted from aluminium oxide this way.
Write a balanced equation for the reduction of zinc oxide by carbon, and identify the reducing agent.
Suggest a method of extraction for each metal: (a) potassium, (b) lead (below iron in the series), (c) gold.
Suggest two reasons why carbon is used to extract metals such as iron.
Suggest why aluminium, though very common in the Earth's crust, was expensive before large-scale electricity was available.
Answer key and marking notes
A rock that contains enough of a metal (compound) to make extraction economically worthwhile.
- Zinc is below carbon in the reactivity series, so carbon can remove oxygen from zinc oxide.
- Aluminium is above carbon, so carbon cannot reduce aluminium oxide; electrolysis is needed.
- 2ZnO + C → 2Zn + CO2 (or ZnO + C → Zn + CO).
- Carbon is the reducing agent.
- (a) electrolysis of a molten potassium compound.
- (b) reduction of lead oxide by carbon.
- (c) found uncombined; no chemical extraction needed.
- Carbon (coke) is cheap and readily available.
- It is more reactive than iron, and burning it also provides the high temperature needed.
- Aluminium is too reactive to be extracted with carbon.
- It can only be extracted by electrolysis, which needs large amounts of electricity.
7 multiple-choice questions on this lesson
From the topic question bank. Assign them in the app for a marked score in your gradebook, or run the topic as a class game.
Nickel is between iron and hydrogen in the reactivity series. Which method would be most suitable for extracting nickel from nickel oxide?
- Aheating nickel oxide with carbon
- Belectrolysis, because every metal must be extracted by electrolysis
- Cnone, because nickel is found uncombined
- Dheating nickel oxide on its own in air
Gold and copper have been used for thousands of years, iron for about 3000 years, but aluminium was first isolated only about 200 years ago. What is the best explanation?
- Athe more reactive a metal is, the harder it is to extract from its compounds
- Baluminium is very rare in the Earth's crust
- Caluminium is less reactive than iron, so it was harder to find
- Dgold and copper are extracted by electrolysis, which was discovered first
A metal is extracted by electrolysis of its molten compound. Where does the metal form?
- Aat the cathode (negative electrode)
- Bat the anode (positive electrode)
- Cin the electrolyte, evenly spread throughout
- Das a gas above the cell
Lead can be extracted by heating lead(II) oxide, PbO, with carbon. Carbon dioxide is also formed. Which is the balanced equation?
- A2PbO + C → 2Pb + CO2
- BPbO + C → Pb + CO2
- C2PbO → 2Pb + O2
- DPbO + C2 → Pb + CO2
Zinc is often mined as zinc blende, ZnS. Why is the ore roasted in air before it is heated with carbon?
- Ato convert zinc sulfide into zinc oxide, which carbon can then reduce
- Bto melt the zinc so it runs out of the rock
- Cto convert zinc sulfide into zinc carbonate
- Dto turn the zinc into a gas that can be collected
Potassium was first isolated only when electrolysis became available, and extracting it still needs a lot of energy. Which statement explains why?
- Apotassium atoms lose electrons very readily, so K+ ions are very difficult to turn back into atoms
- Bpotassium ions gain electrons very readily, so they are easy to reduce
- Cpotassium is found uncombined, so it is hard to separate from other metals
- Dpotassium compounds contain no ions, so they cannot be split by carbon
Extracting a metal from its compound is always described as reduction. In terms of electrons, what happens to the metal?
- Ametal ions gain electrons to form metal atoms
- Bmetal atoms lose electrons to form metal ions
- Cthe metal gains oxygen
- Dthe metal ions lose electrons to form atoms
Quiz key
Nickel is below carbon, so carbon is more reactive and can remove the oxygen from nickel oxide, which is the cheaper method. Electrolysis is needed only for metals above carbon, and it would be far more expensive. Only very unreactive metals such as gold are found uncombined, and nickel is above hydrogen. Heating the oxide alone in air does not remove the oxygen; a reducing agent is needed.
Gold is found uncombined, copper can be reduced from its ores with charcoal at quite low temperatures, iron needs a hotter furnace, and aluminium is above carbon so it needs electrolysis. The order of discovery follows reactivity: the more reactive the metal, the harder its extraction. Aluminium is actually the most common metal in the Earth's crust. It is more reactive than iron, not less. Gold and copper do not need electrolysis, and electricity was not available in ancient times.
Metal ions are positive, so they are attracted to the negative electrode, the cathode, where they gain electrons and form the metal. The anode attracts negative ions such as oxide or chloride ions, which form non-metal products. The metal collects at the cathode rather than spreading through the electrolyte, and metals such as aluminium and sodium are liquids or solids at the cell temperature, not gases.
One carbon atom takes two oxygen atoms to make CO2, so two PbO units are needed: 2PbO + C → 2Pb + CO2, with 2 Pb, 2 O and 1 C on each side. The equation with one PbO has only one oxygen on the left but two on the right. The equation without carbon describes decomposition by heat alone, which does not happen and ignores the carbon dioxide. Carbon is written as C, not C2.
Roasting in air converts the sulfide into the oxide (2ZnS + 3O2 → 2ZnO + 2SO2). Carbon then removes the oxygen from zinc oxide: 2ZnO + C → 2Zn + CO2. The zinc is still combined after roasting, so it cannot simply melt out. Air provides oxygen, not carbonate, and roasting does not release zinc as a gas.
Potassium is at the top of the series because its atoms form K+ ions extremely readily. Extraction must reverse this, forcing electrons back onto K+ ions, which carbon cannot do; only electrolysis supplies enough energy. If K+ ions gained electrons readily, potassium would be easy to extract. Potassium is far too reactive to be found uncombined. Potassium compounds are ionic, which is exactly why they conduct when molten.
In a compound the metal exists as positive ions, for example Cu2+ or Al3+. To become neutral atoms they must gain electrons, and gain of electrons is reduction. Metal atoms losing electrons is oxidation, the reverse of extraction, as happens in corrosion. The metal loses oxygen, not gains it. Losing electrons would make an ion more positive, not neutral.
Slides for this lesson
A projectable deck for every pack is on the way. Until then, present the student lesson full screen: its sections, figure and lab tabs follow the same order as the plan above.