The effect of concentration

2 marks · Normal

For the following equilibrium in solution: State what will happen to the position of equilibrium if more ions are added to the mixture. Explain your answer.

Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.

Show answer

The equilibrium will shift to the right (towards the products), forming more FeSCN2+ ions, because increasing the concentration of a reactant causes the system to oppose the change by forming more product.

Also accept: The equilibrium shifts to the products side to use up the added SCN− ions.; More FeSCN2+ will be formed.

Common mistakes: Saying the equilibrium does not move; Saying fewer products will be made

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Marking points

M1 · 1 mark · States that the equilibrium shifts to the right/towards products or forms more FeSCN2+ ions.

A1 · 1 mark · Explanation: increasing concentration of SCN− causes the system to oppose the change (Le Chatelier's principle) by forming more product.

Worked solution

When the concentration of SCN− ions increases, the equilibrium responds by using up some of the added SCN−.

This is achieved by producing more FeSCN2+ ions, so the position of equilibrium shifts to the right.