# A chemist is analysing a white powder suspected to contain either calcium ions, copper(II) ions or iron(III) ions, as well as either chloride, sulfate or carbonate anions. The chemist dissolves the powder in dilute hydrochloric acid and carries out a series of tests to identify both the cation and the anion present. Describe the observations the chemist would make when carrying out a flame test on the original powder, and state what these observations indicate about which cation is present. Then describe the test and expected observation that would confirm the presence of sulfate ions in the solution.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 2.5 Tests for ions and gases · Describe · 4 marks

> A white powder is dissolved in dilute hydrochloric acid to form a colourless solution. A flame test is then performed on the original white powder. To test for the anion, a few drops of dilute hydrochloric acid followed by a few drops of barium chloride solution are added to a portion of the solution.

## Mark scheme (4 marks)

1. The flame test produces a brick-red / orange-red flame, indicating the presence of calcium ions
2. Add dilute hydrochloric acid (to acidify the solution) followed by barium chloride solution
3. A white precipitate forms
4. The white precipitate is barium sulfate, confirming sulfate ions are present

## Key terms

- [flame test](https://www.gradenine.co.uk/glossary/flame-test)
- [sulfate ions](https://www.gradenine.co.uk/glossary/sulfate-ions)
- [calcium ions](https://www.gradenine.co.uk/glossary/calcium-ions)

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- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-chemist-is-analysing-a-white-c2a6e013) · Published by Druglandscape Ltd.