---
title: "Testing for Ions and Gases"
description: "Identify unknown ions by flame colour and by the precipitate they form, test the common gases at the bench, and say why an instrument beats these tests on a tiny sample."
canonical: https://lightmysky.com/learn/science/testing-for-ions-and-gases-mt_PDZjzQJdVt
source: https://lightmysky.com/learn/science/testing-for-ions-and-gases-mt_PDZjzQJdVt.md
retrieved: 2026-09-12
---

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# Testing for Ions and Gases

Identify unknown ions by flame colour and by the precipitate they form, test the common gases at the bench, and say why an instrument beats these tests on a tiny sample.

Subject: Science · Area: Matter & Materials · Ages 15 to 16
Page: https://lightmysky.com/learn/science/testing-for-ions-and-gases-mt_PDZjzQJdVt

## Ready when they can

- Matches flame colours to the group 1 and group 2 metal ions that produce them
- Predicts the precipitate formed when a halide or a sulfate solution meets its test reagent, and writes the ionic equation
- Describes the bench tests for hydrogen, oxygen, carbon dioxide and chlorine and the result each gives
- Explains a flame colour as electrons dropping back between shells, and gives one reason instruments are used instead

## Lesson: Naming ions and gases at the bench

Titration tells how much acid, not which ion. Flame tests name the metal ion. Lithium burns crimson, sodium burns yellow and potassium burns lilac. Calcium burns orange-red, strontium burns red and barium burns green. The colour appears because electrons jump to higher shells in the heat, then drop back and release light. Colours can look alike, so analysts confirm with instruments such as flame photometers.

Anions are named by precipitates. Add acidified silver nitrate to test halides: chloride gives a white precipitate, bromide gives cream and iodide gives yellow. Add acidified barium chloride to test sulfates: a white precipitate of barium sulfate appears. Each ionic equation shows only the ions that join into the solid, such as Ag+ + Cl- -> AgCl, leaving out the spectators.

**Example.** To show a solution is sodium chloride rather than potassium sulfate, run two tests. A yellow flame points to sodium, while potassium would burn lilac. A white precipitate with acidified silver nitrate points to chloride, while sulfate would stay clear. Both results together name the salt.

Gases each have one bench test. Hydrogen burns with a squeaky pop when you hold a lit splint to it. Oxygen relights a glowing splint. Carbon dioxide turns limewater from clear to milky. Chlorine bleaches damp litmus paper white. Match each result to its gas and never swap the splints.

**Recap.** Flames name the metal, precipitates name the anion, and splints, limewater and litmus name the gas.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Electron Shells and the Shape of the Periodic Table](https://lightmysky.com/learn/science/electron-shells-and-the-shape-of-the-periodic-table-mt__Sdcw4RnZF)
- [Titration: Finding an Unknown Concentration](https://lightmysky.com/learn/science/titration-finding-an-unknown-concentration-mt_7WLN35XxYx)
- [Choosing How to Separate Mixtures](https://lightmysky.com/learn/science/choosing-how-to-separate-mixtures-mt_U_tJvy3cbB)

## Opens up

- [Potable Water and Treating Waste Water](https://lightmysky.com/learn/science/potable-water-and-treating-waste-water-mt_5qsFZJSmMO)
- [Electrolysis: Half Equations at the Electrodes](https://lightmysky.com/learn/science/electrolysis-half-equations-at-the-electrodes-mt_6FvxaD8wTY)
- [Solubility Equilibria and When a Precipitate Appears](https://lightmysky.com/learn/science/solubility-equilibria-and-when-a-precipitate-appears-mt_IMdWLxIAFt)
- [Metal Aqua Ions: Acidity, Ligand Exchange and Precipitation](https://lightmysky.com/learn/science/metal-aqua-ions-acidity-ligand-exchange-and-precipitation-mt_jrsKwNq1Oi)
- [Group 7: Oxidising Power, Displacement and Halide Tests](https://lightmysky.com/learn/science/group-7-oxidising-power-displacement-and-halide-tests-mt_li7olQ3dM9)