# A student dissolves excess solid silver chloride, AgCl(s), in water at 25 °C and allows the system to reach equilibrium. The student then adds a small amount of concentrated sodium chloride solution to the equilibrium mixture. Explain what happens to the position of equilibrium and to the value of Ksp after the sodium chloride is added.

> IB DP Chemistry Standard Level (2023 syllabus) — R2.3 How far? The extent of chemical change · Explain · 4 marks

> The dissolution equilibrium for silver chloride can be represented as: AgCl(s) ⇌ Ag⁺(aq) + Cl⁻(aq)

## Mark scheme (4 marks)

1. Adding sodium chloride increases the concentration of Cl⁻(aq) ions in the mixture.
2. The reaction quotient Qsp becomes greater than Ksp, so the equilibrium position shifts to the left (towards the reactants / towards more AgCl(s)).
3. The shift to the left reduces the concentration of Cl⁻(aq) (and Ag⁺(aq)) until Q equals Ksp again / until equilibrium is re-established.
4. The value of Ksp remains unchanged because temperature has not changed.

## Key terms

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

## Related

- [Revision notes for IB DP Chemistry Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-dissolves-excess-solid-silver-6b2b83eb) · Published by Druglandscape Ltd.