Ion Identification
Hand a chemist an unknown salt and they can name its ions. Learn the flame tests, the sodium hydroxide precipitate tests and the tests for carbonate, sulfate and halide ions, then meet the faster tools of instrumental analysis.
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Naming an unknown salt 🧪
Hand a chemist a white powder and they can work out exactly which **ions** it contains. Every ion has a test that gives it a **unique** result. This module works through the tests: **flame tests** for metals, **sodium hydroxide** for precipitates, and tests for **carbonate**, **sulfate** and **halide** ions.
The language of ion tests 🔑
Four ideas run through this module:
Match each metal ion to its flame colour 🔥
- Li+
- Na+
- K+
- Cu2+
- Red
- Yellow
- Lilac
- Blue-green
Read the flame 🎯
A metal salt gives a LILAC colour in a flame test. Which ion is present?
- K+
- Na+
- Li+
- Cu2+
Testing with sodium hydroxide 🧫
Adding **sodium hydroxide** solution to a dissolved metal salt often gives a coloured **precipitate**. Copper Cu2+ gives a **blue** precipitate, iron Fe2+ a **green** one, and iron Fe3+ a **brown** one. Aluminium Al3+ and calcium Ca2+ both give a **white** precipitate, but only the Al3+ one **dissolves in excess** sodium hydroxide. Ammonium NH4+ gives off ammonia gas when warmed, turning damp red litmus paper blue.
Match each ion to its hydroxide precipitate 🔗
- Cu2+
- Fe2+
- Fe3+
- Al3+
- A blue precipitate
- A green precipitate
- A brown precipitate
- A white precipitate that dissolves in excess
Which give white? ⚪
Select the TWO ions that give a WHITE precipitate with sodium hydroxide solution.
- Al3+
- Ca2+
- Cu2+
- Fe3+
Testing positive and negative ions ⚗️
Different families of test identify the positive ions and the negative ions in a salt.
Testing for a halide 🪜
An interactive activity.
Ion tests in words 🧩
A flame test names metal ions by colour: sodium burns _____ and potassium burns _____. Adding sodium hydroxide to iron Fe2+ gives a _____ precipitate. A carbonate fizzes with acid and turns limewater _____. A sulfate gives a white precipitate with barium _____.
Read the precipitate 🟡
Adding silver nitrate to a solution gives a YELLOW precipitate. Which halide ion is present?
- Iodide
- Chloride
- Bromide
- Sulfate
Spot the true statements 🖍️
An interactive activity.
Identify the salt 🕵️
An interactive activity.
Identify the ions ✍️
An interactive activity.