DSE Chemistry | Qualitative Analysis and Ion Tests: Tutor Lesson Plan

2026-11-03

Tutor lesson-prep guides · Secondary Chemistry

Students memorise a dozen observations as vocabulary and collapse on an unseen solution. This lesson replaces memory with an order: colour, flame, sodium hydroxide to excess, then anions, with solubility in excess as the deciding fact.

Objectives — Students can: (1) recall golden yellow for sodium, lilac for potassium, brick red for calcium and blue-green for copper; (2) use sodium hydroxide to identify the blue precipitate of copper, the green turning brown of iron(II), the red-brown of iron(III), and separate zinc from aluminium with excess ammonia; (3) test carbonate, sulphate and halides with acid, barium chloride and silver nitrate in that order; (4) write an ordered test plan for an unknown rather than adding reagents at random.

01 Prerequisites (3-minute check)

If any of these fails, fix it before the lesson starts.

Skill	Quick check	Pass mark
Definition of a precipitate	What is the solid formed when two solutions react?	A precipitate
Colour of ions	What colour is copper(II) in solution?	Blue
Acid reactions	What gas do carbonates release with dilute acid?	Carbon dioxide
Solubility	Is silver chloride soluble in water or in ammonia?	Insoluble in water, soluble in ammonia

02 Lesson flow (60 minutes)

Time	Stage	Tutor does	Student does
0-8 min	Two unknown bottles	Show two colourless solutions and ask how to tell them apart	Answer with a test, not a guess
8-20 min	Flame tests	Dip a clean wire into sodium, potassium, calcium and copper salts	State four colours and when they apply
20-34 min	Sodium hydroxide	Add dropwise then to excess for four cases	List colour and whether it dissolves
34-44 min	Ammonia	Use ammonia to separate zinc from aluminium	Explain why this step decides
44-54 min	Anions	Show acid, barium chloride, silver nitrate in order	Put the tests in a defensible order
54-60 min	Independent practice	One unknown in six minutes	Write a complete test plan

03 Teaching script (read it out)

Scene 1: A flame colour is an entry ticket, not the answer

A flame test identifies the metal only, and it needs a clean wire, otherwise sodium from the last sample drowns everything. Sodium is golden yellow, potassium lilac and best seen through cobalt glass, calcium brick red, copper blue-green. Students try to use flames for every ion, but transition metals are often weak, so a precipitate test must follow. Teach the scope of the test, not just the colours.

Ask why potassium lilac is viewed through blue cobalt glass.

Scene 2: Add sodium hydroxide dropwise, then to excess

A few drops already give a precipitate, but the mark comes from what happens in excess. Copper gives a blue precipitate that stays, iron(II) gives green that browns in air, iron(III) gives red-brown, and both zinc and aluminium give white that dissolves in excess alkali. Insist on two pieces of information: colour, and behaviour in excess. Lead also dissolves, which is the fourth white answer.

Ask which three ions give a white precipitate soluble in excess sodium hydroxide.

Scene 3: Ammonia separates zinc from aluminium

Zinc and aluminium both dissolve in excess sodium hydroxide, so alkali alone cannot tell them apart. In excess ammonia, zinc forms a soluble complex while aluminium does not, and that is the discriminator. Anions follow a similar order: add dilute acid first for carbonate, then barium chloride for sulphate, then silver nitrate for halides. The order cannot be reversed because silver ions precipitate carbonate and sulphate as well.

Ask for the order of the three anion tests and the reason for it.

04 Question types and worked steps

Type	Example	Steps	Answer
Flame colour	An unknown salt burns lilac	Read the colour, name the metal, note the cobalt glass	Potassium
Cation table	Sodium hydroxide gives a green precipitate that browns	Colour, then excess behaviour, then the ion	Iron(II)
Separating identical colours	Two unknowns both give white precipitates	Add excess alkali, then excess ammonia, compare	The one soluble in ammonia is zinc
Three anion tests	Acid gives bubbles and barium chloride gives a white solid	Acid first, then barium, then silver	Carbonate and sulphate present

Sanity check (teach this): Logic check: a solution cannot give brisk effervescence with acid and a heavy white precipitate with barium chloride without carbonate interference, because barium carbonate is also white. Every white precipitate must be rechecked with dilute hydrochloric acid: what dissolves is carbonate, what remains is sulphate. Colours also need timing, since iron(II) green browns in air and can be mistaken for iron(III).

05 Independent practice (3 questions)

Question	Answer	What to watch
The ion giving a golden yellow flame	Sodium	Confused with potassium lilac
White precipitate with alkali, soluble in excess alkali but not in ammonia	Aluminium	Think through the ammonia step
White precipitate with barium chloride, insoluble in dilute acid	Sulphate	Used acid to rule out carbonate

06 Common mistakes and what to say

Mistake	Student writes	Say this
Stopping at the flame test	The flame is golden yellow, so it is a sodium salt	The flame only names the metal; it does not tell chloride from carbonate, so an anion test is still needed.
Omitting the excess behaviour	Sodium hydroxide gives a white precipitate	Four ions give white; you must state whether it dissolves in excess and what ammonia does.
Reversing the anion order	Add silver nitrate first, then acid	Silver precipitates carbonate and sulphate too; remove carbonate with acid first so later results mean something.
Ignoring air oxidation	The precipitate is green, so it is iron(III)	Iron(III) is red-brown; green turning brown is iron(II) being oxidised, so note the timing.

07 Homework (paper, section and question numbers)

Chemistry chapter index — Revise acid-base titration, then questions 1 and 2
Acid-base titration — Question 3 also depends on observing an endpoint
Equilibrium and Le Chatelier — Do the multiple choice only, for condition reasoning

08 Exit check (last 5 minutes)

Question	Answer	Decision
Ion giving a lilac flame	Potassium	Error: wrote sodium
Ion giving a blue precipitate with alkali	Copper(II)	Error: confused with iron(II)
White precipitate soluble in excess ammonia	Zinc	Error: wrote aluminium
White precipitate with barium chloride, insoluble in acid	Sulphate	Error: no acid control

09 Tutor FAQ

Why use dilute nitric acid rather than hydrochloric for halides?

Hydrochloric acid contains chloride and would give a false positive; nitric acid introduces no halide.

Do all metals give a flame colour?

No. Many transition metals are weak, so flame tests cover a few metals and precipitates cover the rest.

Can tests be run in sequence on one sample?

Yes, but clean the wire and test tube between tests, otherwise residues give false results.

Find a tutor — free Tutor Registration →

A TutorZone lesson-prep guide. Written by the TutorZone team; questions and lesson flow are original and are not taken from any school or publisher material.