# A water company suspects that a sample of borehole water contains dissolved metal ions and negative ions (anions). A technician carries out qualitative analysis on the water sample and observes a brick-red flame colour during a flame test. When dilute hydrochloric acid and then barium chloride solution are added to a separate portion of the water sample, a white precipitate forms. Identify the metal ion and the negative ion present in the water sample, and describe what each result tells the technician.

> Edexcel GCSE Chemistry (1CH0) — 9.1 Qualitative analysis: tests for ions (Chem only) · Describe · 4 marks

> A water company suspects that a sample of borehole water contains dissolved metal ions and negative ions (anions). A technician carries out qualitative analysis on the water sample. During a flame test, a brick-red colour is observed. When dilute hydrochloric acid followed by barium chloride solution is added to a separate portion of the sample, a white precipitate forms.

## Mark scheme (4 marks)

1. The brick-red flame colour identifies the metal ion as calcium (Ca²⁺)
2. The flame test is a qualitative analysis test used to identify metal ions (cations) by observing the colour produced in the flame
3. The white precipitate formed with barium chloride solution (after acidification with dilute hydrochloric acid) identifies the negative ion as sulfate (SO₄²⁻)
4. The white precipitate forms because barium sulfate is insoluble and precipitates out of solution when barium ions react with sulfate ions

## Key terms

- [qualitative analysis](https://www.gradenine.co.uk/glossary/qualitative-analysis)
- [flame test](https://www.gradenine.co.uk/glossary/flame-test)
- [precipitate](https://www.gradenine.co.uk/glossary/precipitate)

## Related

- [Revision notes for Edexcel GCSE Chemistry (1CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-water-company-suspects-that-a-1be732c9) · Published by Druglandscape Ltd.