# Seawater contains many dissolved substances. A scientist collects seawater samples from two locations: one near a busy shipping lane and one from a remote area of the open ocean far from human activity. The scientist measures the concentration of several dissolved ions in each sample. Describe what is meant by the term 'solution' and explain why seawater is considered a complex solution containing many different dissolved substances.

> OCR A-Level Chemistry B: Salters (H433) — OC Oceans · Describe and Explain · 5 marks

> Seawater is sometimes described as a complex solution. It contains dissolved salts, gases, and other substances that have entered the oceans through a variety of natural and human processes over millions of years.

## Mark scheme (5 marks)

1. A solution is a mixture formed when a solute dissolves in a solvent
2. In seawater, water is the solvent
3. Seawater contains many different solutes / dissolved substances such as sodium chloride or other named salts or dissolved gases
4. Rivers carry dissolved minerals / ions into the sea from the weathering or erosion of rocks on land
5. Gases such as carbon dioxide or oxygen dissolve from the atmosphere into seawater, adding to its complexity

## Key terms

- [solution](https://www.gradenine.co.uk/glossary/solution)
- [dissolved](https://www.gradenine.co.uk/glossary/dissolved)

## Related

- [Revision notes for OCR A-Level Chemistry B: Salters (H433)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/seawater-contains-many-dissolved-substances-a-57f27f3d) · Published by Druglandscape Ltd.