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Lesson 6

Lesson 6: Anion & Water Tests 🧪

Identifying Negative Ions & Water

🧪⬜🟨💧🫧
Learning Objectives:
  • 2.48 – Describe tests for halide (Cl⁻, Br⁻, I⁻), sulfate and carbonate ions.
  • 2.49 – Describe the test for water using anhydrous copper(II) sulfate.

🏆 By the end I will be able to…

All: name the reagent and the result for the halide, sulfate and carbonate tests.

Most: describe each test fully, and the water test, using the correct acid each time.

Some: explain why HNO₃ (not HCl) is used for halides, and write the ionic equations.

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Teacher Print Tools – Lesson 6

⏱️ Before We Start · 60 sec

Before We Start: Anion & Water Tests in 60 Seconds

New to this? Flame tests found the metal (the cation). Today we find the negative ion (the anion) — and test for water. (All on Side A of your bridge sheet.)

Each anion has its own test

Halidessilver nitrateWhite/Cream/YellowSulfatebarium chlorideWhite pptCarbonatedilute HClFizz → milkyWateranhydrous CuSO₄White → Blue

A different reagent for each ion — and a colour change for water.

1. Halides (Cl⁻/Br⁻/I⁻): add dilute nitric acid, then silver nitrate → white / cream / yellow precipitate.
2. Sulfate: add dilute HCl, then barium chloride → white precipitate. Carbonate: add HCl → it fizzes (CO₂ → limewater milky).
3. Water: anhydrous copper sulfate goes from white → blue.
Whiteboards — 20 seconds: which reagent finds halides? Which ion makes a powder fizz? Then we go straight into the tests.
⭐ Fab 4

The Fab 4 – Recall to Get You Started

Instructions: Multiple choice — in your books, write the letter you think is right. No calling out. Reveal when ready.

1. Sodium

What colour flame does Na⁺ produce?

A) Crimson redB) YellowC) LilacD) Blue-green

✅ B) Yellow.

2. Copper

Which ion gives a blue-green flame?

A) Li⁺B) K⁺C) Cu²⁺D) Ca²⁺

✅ C) Cu²⁺ (copper).

3. The first step

The first step of a flame test is to…

A) clean the wire in conc. HClB) dip it in the sampleC) light the Bunsen

✅ A) Clean the wire in concentrated HCl.

4. Today\u2019s lead-in

Flame tests find the metal (cation). How might you find the negative ion?

A) weigh itB) a different chemical test for the anionC) smell it

✅ B) Use a different chemical test for the anion — today\u2019s lesson.

Starter

🕵️ Starter: Anion Detective

Your mission: Four students described an anion test. Only ONE is fully correct — the others hide a mistake (watch the acid!). Decide in your book first, then tap a suspect to investigate. No calling out!
Suspect A“For chloride: add hydrochloric acid, then silver nitrate → white precipitate.”tap to investigate ▸
Suspect B“For sulfate: add barium chloride → cream precipitate.”tap to investigate ▸
Suspect C“For iodide: add nitric acid, then silver nitrate → yellow precipitate.”tap to investigate ▸
Suspect D“For carbonate: add silver nitrate → it fizzes.”tap to investigate ▸
🧠 Detective’s hint: two questions — which reagent, and which acid? Halides = nitric acid + silver nitrate. Sulfate = HCl + barium chloride. Carbonate = HCl (fizz).
Aspire: for each imposter, give its “alibi” — say exactly what’s wrong and the correct version.
I Do

I Do: The Anion Tests & the Water Test (2.48 & 2.49)

Key Idea: each negative ion has its own test. Acidify first, then add the reagent and read the result. Get the acid right and the marks follow.

🧪 Halides & Sulfate

Halides (Cl⁻, Br⁻, I⁻): add dilute nitric acid, then silver nitrate (AgNO₃).

Cl⁻
White ppt
Br⁻
Cream ppt
I⁻
Yellow ppt

Sulfate (SO₄²⁻): add dilute HCl, then barium chloride (BaCl₂) → white precipitate (BaSO₄).

🫧 Carbonate & 💧 Water

Carbonate (CO₃²⁻): add dilute HCl → it fizzes; bubble the gas through limewater → it turns milky (CO₂).

CO₃²⁻ + 2H⁺ → H₂O + CO₂

Water (2.49): add the liquid to anhydrous copper(II) sulfate (white) → it turns blue.

CuSO₄ (white) + 5H₂O → CuSO₄·5H₂O (blue)

🎯 Examiner trap: use NITRIC acid (not HCl) to acidify for halide tests. HCl adds Cl⁻ ions → a false white precipitate. Acidifying first also removes carbonate that could give a false positive.

🧠 Memory aid: down the halides the precipitate gets darker — White → Cream → Yellow. “Cloud → Butter → Yolk.”

Don’t write: add HCl then silver nitrate (halide test)

Write: add dilute NITRIC acid, then silver nitrate

HCl contains Cl⁻ — it would give a false white precipitate with silver nitrate.

Talk to your partner: which test uses nitric acid and which uses hydrochloric acid — and why does it matter? Be ready to run the lab next.
🧪 Observe

Observe: The Precipitate Lab

Watch & check: test all six samples. Before each one, say the result you predict, then tap. Notice the acid going in first every time — that\u2019s the \u201cwhy acidify\u201d step made visible.

🧪 THE PRECIPITATE LAB — tap a sample to test it

⚠ EYE PROTECTION Tap a test tube to add the reagent Cl⁻ ✓ Br⁻ ✓ I⁻ ✓ SO₄²⁻ ✓ CO₃²⁻ ✓ H₂O ✓
Acid goes in FIRST on each test · results stay until reset
👀 Say it as you test: “I add ____, then ____, and see a ____ precipitate, so the ion is ____.”
🌟 Spot it: three tests give a white result (Cl⁻, SO₄²⁻ ppt). What tells them apart? The reagent and the acid you used.
Ready check: cover the screen — can you name the reagent AND result for halides, sulfate and carbonate? If yes, you’re ready to be a detective next.
We Do

We Do: Detective Lab — Name the Compound 🕵️

The whole series, together: each case file gives you a flame test (the metal) and an anion test (the negative ion). Read the clues, then tap the compound. Three cases to crack.
Cases solved: 0/3   ·   Streak: 0 🔥

Case 1 of 3

🔎 Name the compound:

🧡 Tip: two clues = two ions. The flame gives the metal (cation); the precipitate or fizz gives the anion. Put them together for the compound.
Independent Work

Independent Work – Anion & Water Tests

Instructions: Complete your printed worksheet at your level. You may use the tests table from the lab and the knowledge organiser. ❌ Never write “add HCl then silver nitrate” — halides need nitric acid.
Independent Work Timer
08:00

Foundation (Grades U–1)

Complete the tests table, circle the right answers, and a short chloride-test question.

Middle (Grades 2–3)

State the precipitate colours, explain the nitric-acid rule, then a fizz/limewater exam question.

Higher (Grades 3–5)

Write the ionic equations, explain the reversible water test, then a 6-mark unknown-compound question.

📋 Scaffolding

Every pack includes the colour table, the method, sentence starters and word banks. Use them whenever you need them — that’s what they’re for.

🏆 Success Criteria

Foundation (U–1): I can name the reagent and result for the halide, sulfate and carbonate tests.

Middle (2–3): I can describe each test fully and explain why nitric acid is used for halides.

Higher (3–5): I can write the ionic equations and explain the reversible water test.

Exit Ticket

Exit Ticket – Chemical Analysis (Lessons 4–6)

Knowledge check — the whole series: six questions across gas tests, flame tests and anion tests. Tap your answer for instant feedback and a score. Books closed, no notes!
Score: 0/6
🖨️ Print written exit ticket:
Slide 1/9

🎉 Lesson Complete!

Anion & Water Tests — Lesson 6

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