The shape of the lesson
By the end of the lesson, learners can
- Indicators and ions: Add an acid, then an alkali, to each indicator in the simulator and note the colours.
- Reactions of acids: Every reaction of an acid on this page produces a salt.
- Metal: salt + hydrogen.
- Base: salt + water.
- Carbonate: salt + water + carbon dioxide.
- Indicators: litmus red/blue, methyl orange red/yellow, thymolphthalein colourless/blue.
One picture every idea returns to
Acids turn blue litmus red, turn methyl orange red and leave thymolphthalein colourless. They react with metals to give a salt and hydrogen, with bases to give a salt and water, and with carbonates to give a salt, water and carbon dioxide. Bases are oxides or hydroxides of metals; soluble bases are alkalis. Alkalis turn red litmus blue, methyl orange yellow and thymolphthalein blue, and release ammonia from ammonium salts. Acids contain H+ ions and alkalis contain OH− ions.
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, Sour, soapy and salty.. Acids react with metals, bases and carbonates, and every one of those reactions makes a salt. 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: Indicators and ions | Add an acid, then an alkali, to each indicator in the simulator and note the colours. Project tab 5 of the lab (Equilibria lab, acids and bases) and let a student drive it while the class predicts. | Whole class, then pairs |
| 17 to 30 min | Teach and check: Reactions of acids | Every reaction of an acid on this page produces a salt. | 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, 14 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 Reactions of acids, 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 |
|---|---|
| Metal + acid gives hydrogen; carbonate + acid gives carbon dioxide. | Mixing these up is the commonest slip. Also, a base is not always an alkali: say "alkali" only for a base that dissolves in water. |
Properties of acids and bases: worksheet
6 questions, 14 marks. Written in the style of the papers; no past paper question is reproduced.
State the colour of (a) litmus, (b) methyl orange and (c) thymolphthalein in an alkaline solution.
Write word equations for the reactions of dilute hydrochloric acid with (a) zinc, (b) calcium oxide and (c) sodium carbonate.
Write the balanced symbol equation for the reaction of magnesium with dilute sulfuric acid, and describe one observation.
Explain the difference between a base and an alkali, giving one example of each.
Describe a test to show that a fertiliser contains ammonium ions.
Write the ionic equation, with state symbols, for the reaction between any acid and any alkali, and name the type of reaction.
Answer key and marking notes
- (a) blue
- (b) yellow
- (c) blue
- (a) zinc + hydrochloric acid → zinc chloride + hydrogen
- (b) calcium oxide + hydrochloric acid → calcium chloride + water
- (c) sodium carbonate + hydrochloric acid → sodium chloride + water + carbon dioxide
- Mg + H2SO4 → MgSO4 + H2
- Fizzing (bubbles) and the magnesium gets smaller or disappears.
- A base reacts with an acid to form a salt and water; an alkali is a base that dissolves in water.
- Example base: copper(II) oxide (insoluble). Example alkali: sodium hydroxide.
- Warm the fertiliser with aqueous sodium hydroxide.
- Ammonia is given off, which turns damp red litmus paper blue.
- H+(aq) + OH−(aq) → H2O(l)
- Neutralisation.
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.
A few drops of methyl orange turn a solution yellow, and a few drops of thymolphthalein turn a second sample of the same solution blue. What does this show about the solution?
- AIt is alkaline.
- BIt is acidic.
- CIt is neutral.
- DIt contains no ions.
Which salt is formed when aqueous potassium hydroxide is neutralised by dilute sulfuric acid?
- Apotassium sulfate
- Bpotassium sulfide
- Cpotassium sulfite
- Dpotassium nitrate
A small piece of copper foil is dropped into dilute hydrochloric acid. What is observed?
- AThere is no visible reaction.
- BThe copper fizzes and hydrogen is given off.
- CThe copper fizzes and carbon dioxide is given off.
- DThe copper dissolves to form a green solution of copper(II) chloride.
Which pair of reactants produces a salt, water and carbon dioxide?
- Acalcium carbonate and dilute nitric acid
- Bcalcium and dilute nitric acid
- Ccalcium oxide and dilute nitric acid
- Dcalcium hydroxide and dilute nitric acid
Dilute hydrochloric acid is added to a white powder, X. The mixture fizzes, and the gas turns limewater milky. What could X be?
- Asodium carbonate
- Bmagnesium
- Csodium hydroxide
- Dzinc oxide
Which list contains only alkalis?
- Asodium hydroxide, potassium hydroxide, aqueous ammonia
- Bsodium hydroxide, copper(II) oxide, calcium hydroxide
- Cmagnesium oxide, iron(III) hydroxide, potassium hydroxide
- Dhydrochloric acid, sodium hydroxide, aqueous ammonia
Solid ammonium sulfate is warmed with aqueous sodium hydroxide. Which products form?
- Asodium sulfate, water and ammonia
- Bsodium sulfate and hydrogen
- Csodium sulfate, water and nitrogen
- Dsodium ammonium sulfate and oxygen
Which is the balanced equation for the reaction of sodium carbonate with dilute nitric acid?
- ANa2CO3 + 2HNO3 → 2NaNO3 + H2O + CO2
- BNa2CO3 + HNO3 → NaNO3 + H2O + CO2
- CNa2CO3 + 2HNO3 → 2NaNO3 + H2 + CO2 + O2
- DNa2CO3 + 2HNO3 → Na2(NO3)2 + H2CO3
Quiz key
Methyl orange is red in acid and yellow in alkali, and thymolphthalein is colourless in acid and blue in alkali. Both indicators are showing their alkali colours, so the solution is alkaline. An acidic solution would turn methyl orange red and leave thymolphthalein colourless. A neutral solution would not turn thymolphthalein blue. Indicator colour changes depend on the ions present, so the solution does contain ions (hydroxide ions).
Sulfuric acid, H2SO4, contains the sulfate group, so it always forms sulfates; potassium comes from the alkali. The product is potassium sulfate, K2SO4. A sulfide contains sulfur with no oxygen, and a sulfite comes from sulfurous acid, not sulfuric acid. Potassium nitrate would need nitric acid.
Copper is a very unreactive metal, below hydrogen in the reactivity series, so it does not react with dilute hydrochloric acid and nothing is seen. Reactive metals such as magnesium or zinc fizz and give hydrogen, but copper does not. Carbon dioxide comes only from carbonates reacting with acids, never from a metal. No copper(II) chloride forms, because there is no reaction.
An acid reacts with a carbonate to form a salt, water and carbon dioxide: calcium carbonate + nitric acid gives calcium nitrate + water + carbon dioxide. Calcium metal with an acid gives a salt and hydrogen, not carbon dioxide. Calcium oxide and calcium hydroxide are bases, so with an acid they give only a salt and water; neither contains carbon.
Limewater turns milky with carbon dioxide, and carbon dioxide is produced when an acid reacts with a carbonate, so X is sodium carbonate. Magnesium would fizz but give hydrogen, which does not affect limewater (and magnesium is a grey metal, not a white powder). Sodium hydroxide and zinc oxide are bases: they neutralise the acid to give a salt and water with no gas at all.
Sodium hydroxide, potassium hydroxide and aqueous ammonia all dissolve in water to give OH− ions, so all three are alkalis. Copper(II) oxide, magnesium oxide and iron(III) hydroxide are bases, but they are insoluble in water, so they are not alkalis. Hydrochloric acid is an acid, not an alkali.
Alkali + ammonium salt gives a salt + water + ammonia: (NH4)2SO4 + 2NaOH → Na2SO4 + 2H2O + 2NH3. Hydrogen is the product of a metal with an acid, not of this reaction. The nitrogen stays combined in ammonia; it is not released as nitrogen gas. No oxygen is produced.
The products must be sodium nitrate, water and carbon dioxide. Sodium nitrate is NaNO3, so the two sodium atoms in Na2CO3 need 2NaNO3, and that needs 2HNO3. Both sides then have 2 Na, 2 H, 2 N, 1 C and 9 O. The version with only one HNO3 has unequal numbers of sodium atoms. The version with H2 and O2 gases is wrong because water is formed, not separate hydrogen and oxygen. Na2(NO3)2 is not a correct formula, because each Na+ ion pairs with one NO3− ion.
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.