The shape of the lesson
By the end of the lesson, learners can
- Across the Periodic Table: Step through the oxides of Period 3 in the simulator.
- Amphoteric oxides: Extended.
- Basic oxides (metals) react with acids.
- Acidic oxides (non-metals) react with bases.
- Amphoteric (Al2O3, ZnO) react with both.
- Across a period: basic → amphoteric → acidic.
One picture every idea returns to
Basic oxides are oxides of metals, such as calcium oxide and copper(II) oxide; they react with acids to form a salt and water. Acidic oxides are oxides of non-metals, such as carbon dioxide and sulfur dioxide; they react with bases to form a salt and water, and many dissolve in water to give acidic solutions. Extended: amphoteric oxides, such as aluminium oxide and zinc oxide, react with both acids and bases.
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, Which side of the table?. Burn an element in oxygen and the oxide tells you whether it was a metal or a non-metal. 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: Across the Periodic Table | Step through the oxides of Period 3 in the simulator. Project tab 3 of the lab (Periodicity lab, the oxides) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Amphoteric oxides | Extended. | Jot Thoughts |
| 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, 15 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 Amphoteric oxides, 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.
Jot Thoughts
Teams write ideas on slips, one idea per slip, as many as they can in two minutes, saying each aloud as they place it in the middle. Then they sort the slips, which is where the structure of the topic appears.
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 |
|---|---|
| Not every metal oxide is simply basic: aluminium and zinc oxides are amphoteric. | And "acidic oxide" means it reacts with bases; it does not contain hydrogen ions itself. Silicon dioxide is acidic even though it does not dissolve in water. |
Acidic, basic and amphoteric oxides: worksheet
6 questions, 15 marks. Written in the style of the papers; no past paper question is reproduced.
Classify each oxide as acidic or basic: (a) calcium oxide, (b) carbon dioxide, (c) copper(II) oxide, (d) sulfur dioxide.
Explain how the type of oxide formed by an element can help to show whether the element is a metal or a non-metal.
Write a word equation and a balanced symbol equation for the reaction of magnesium oxide with dilute nitric acid.
(Extended) Define amphoteric oxide and name one example.
(Extended) Describe experiments to show that zinc oxide is amphoteric but magnesium oxide is not.
Explain why burning sulfur-containing fuels can lead to acid rain.
Answer key and marking notes
- (a) basic
- (b) acidic
- (c) basic
- (d) acidic
- Metals form basic oxides, which react with acids.
- Non-metals form acidic oxides, which react with bases (and often give acidic solutions in water).
- magnesium oxide + nitric acid → magnesium nitrate + water
- MgO + 2HNO3 → Mg(NO3)2 + H2O
- An oxide that reacts with both acids and bases.
- Aluminium oxide (or zinc oxide).
- Add each oxide to dilute hydrochloric acid: both react (dissolve).
- Add each oxide to aqueous sodium hydroxide: zinc oxide reacts (dissolves); magnesium oxide does not.
- Reacting with both acid and base shows zinc oxide is amphoteric; magnesium oxide is basic only.
- Sulfur burns to form sulfur dioxide, an acidic oxide.
- Sulfur dioxide dissolves in rainwater (and is oxidised) to form an acidic solution, acid rain.
8 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.
An element burns in oxygen to form a white solid oxide. The oxide reacts with aqueous sodium hydroxide to form a salt and water, but it does not react with dilute hydrochloric acid. Which element could it be?
- Aphosphorus
- Bmagnesium
- Ccalcium
- Dcopper
A lake has become too acidic. Which oxide could be added to the lake to raise its pH?
- Acalcium oxide
- Bsulfur dioxide
- Ccarbon dioxide
- Dnitrogen dioxide
How does the character of the oxides change across Period 3, from sodium oxide on the left to sulfur dioxide on the right?
- Afrom basic to acidic
- Bfrom acidic to basic
- Cfrom amphoteric to basic
- Dthey are all basic
Magnesium ribbon is burned in air. The white ash is shaken with water and a few drops of universal indicator are added. What colour is seen, and why?
- Ablue, because magnesium oxide is a basic oxide
- Bred, because magnesium oxide is an acidic oxide
- Cgreen, because all metal oxides are neutral
- Dorange, because oxides always give acidic solutions
Aluminium oxide reacts with dilute hydrochloric acid: Al2O3 + nHCl → 2AlCl3 + 3H2O. What is the value of n, and how is the aluminium oxide behaving?
- A6; as a base
- B3; as a base
- C6; as an acid
- D3; as an acid
Zinc oxide dissolves in warm aqueous sodium hydroxide to form a salt and water. In this reaction, zinc oxide is acting as:
- Aan acid, because it reacts with a base
- Ba base, because it reacts with a base
- Can alkali, because it dissolves in the solution
- Da basic oxide, because zinc is a metal
Three oxides are tested. Oxide J reacts with dilute acid but not with aqueous alkali. Oxide K reacts with aqueous alkali but not with dilute acid. Oxide L reacts with both. Which row identifies J, K and L correctly?
- AJ magnesium oxide, K sulfur dioxide, L zinc oxide
- BJ sulfur dioxide, K magnesium oxide, L zinc oxide
- CJ zinc oxide, K sulfur dioxide, L magnesium oxide
- DJ magnesium oxide, K zinc oxide, L sulfur dioxide
A powder is a mixture of iron(III) oxide, which is basic, and aluminium oxide. Which reagent could be added to dissolve only the aluminium oxide, so that the iron(III) oxide can be filtered off?
- Aaqueous sodium hydroxide
- Bdilute hydrochloric acid
- Cdilute sulfuric acid
- Ddistilled water
Quiz key
Reacting with a base (sodium hydroxide) to form a salt and water, but not with an acid, is the behaviour of an acidic oxide, and acidic oxides are formed by non-metals. Phosphorus is a non-metal; its oxide, P4O10, is a white acidic solid. Magnesium, calcium and copper are metals, so their oxides are basic: they react with hydrochloric acid, not with sodium hydroxide.
Calcium oxide is the oxide of a metal, so it is a basic oxide: it neutralises the acid and raises the pH towards 7 (in practice, lime is used for this). Sulfur dioxide, carbon dioxide and nitrogen dioxide are oxides of non-metals, so they are acidic oxides. Adding them would lower the pH further; sulfur dioxide and nitrogen dioxide are in fact major causes of acid rain.
Across a period the elements change from metals to non-metals. Metal oxides such as sodium oxide are basic, and non-metal oxides such as sulfur dioxide are acidic, so the oxides change from basic to acidic. The reverse order has the pattern backwards. Amphoteric oxides (such as aluminium oxide) appear in the middle of the period, not at the start. Oxides of non-metals are not basic.
Magnesium is a metal, so magnesium oxide is a basic oxide. The little that dissolves forms magnesium hydroxide, giving a weakly alkaline solution (about pH 9 to 10) that turns universal indicator blue. Red would mean an acidic solution, which comes from a non-metal oxide. Metal oxides are basic, not neutral. Not all oxides give acidic solutions: only non-metal oxides do.
The right-hand side has 2AlCl3, which contains 6 chlorine atoms, so n = 6; the 6 hydrogen atoms from 6HCl then match the 3H2O. Aluminium oxide is reacting with an acid to form a salt and water, so here it is behaving as a base. With n = 3 the chlorine and hydrogen do not balance. Aluminium oxide does act as an acid, but only when it reacts with a base such as sodium hydroxide, not in this reaction.
Sodium hydroxide is a base, and a substance that reacts with a base to form a salt and water is behaving as an acid. Zinc oxide is amphoteric, so in this reaction it plays the acidic role; with an acid it would play the basic role. A base does not neutralise another base. Dissolving in sodium hydroxide solution does not make it an alkali. Although zinc is a metal, its oxide is amphoteric rather than simply basic, which is exactly what this reaction shows.
J reacts only with acid, so it is basic: magnesium oxide, a metal oxide. K reacts only with alkali, so it is acidic: sulfur dioxide, a non-metal oxide. L reacts with both, so it is amphoteric: zinc oxide. The row with J and K swapped matches each oxide to the opposite behaviour. Rows that place zinc oxide as J or K treat an amphoteric oxide as if it reacted only one way, and magnesium oxide and sulfur dioxide are not amphoteric.
Aluminium oxide is amphoteric, so it reacts with (dissolves in) a base such as sodium hydroxide solution. Iron(III) oxide is a basic oxide and does not react with an alkali, so it stays as a solid and can be filtered off. Dilute hydrochloric acid and dilute sulfuric acid would react with both oxides, because both can behave as bases. Neither oxide dissolves in water, so water would not separate them.
What to project
The student lesson embeds these tabs. Open them full screen on the projector; every slider has a drag handle on the stage.
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.