# Explain how the polarity of water molecules enables water to act as a solvent for ionic compounds.

> IB DP Biology Higher Level (2023 syllabus) — A1.1 Water · Explain · 4 marks

## Mark scheme (4 marks)

1. Water molecules are polar / have an uneven distribution of charge, with a partial negative charge (δ−) on the oxygen atom and partial positive charges (δ+) on the hydrogen atoms.
2. The δ− oxygen atoms are attracted to the positive ions (cations) and the δ+ hydrogen atoms are attracted to the negative ions (anions) of the ionic compound.
3. Water molecules surround / orientate around the individual ions, forming a hydration shell, which separates the ions from each other.
4. The electrostatic attractions between water molecules and ions overcome the lattice / ionic bonds holding the compound together, allowing the compound to dissociate and dissolve.

## Key terms

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

## Related

- [Revision notes for IB DP Biology Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "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/explain-how-the-polarity-of-water-864b66cc) · Published by Druglandscape Ltd.