A student is comparing equilibrium constants for two different aqueous systems at \(25^\circ\text{C}\).
System 1 (ionic dissociation): Solid calcium fluoride is shaken with distilled water until equilibrium is reached:
\$\(\text{CaF}_2(s) \rightleftharpoons \text{Ca}^{2+}(aq) + 2\text{F}^-(aq)\)\$
The solubility product is \(K_{sp}(\text{CaF}_2)=1.5\times 10^{-10}\).
System 2 (weak acid dissociation): A solution is prepared by dissolving ethanoic acid to make \(0.100\ \text{mol L}^{-1}\) \(\text{CH}_3\text{COOH}(aq)\). The acid dissociation constant is \(K_a(\text{CH}_3\text{COOH})=1.8\times 10^{-5}\).
Assume activity coefficients are 1, volumes are additive, and temperature remains constant.
Write the equilibrium expression for \(K_{sp}\) of calcium fluoride. Explain why the solid does not appear in the expression.
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Create Free Account Log inThis is a free HSC HSC Chemistry practice question worth 3 marks, testing your understanding of Ksp expressions and solubility. It falls under Solution Equilibria in Module 5: Module 5: Equilibrium and Acid Reactions. Submit your answer above to receive instant AI-powered marking and personalised feedback.
Chemical systems may be open or closed. They include physical changes and chemical reactions that can result in observable changes to a system. Students study the effects of changes in temperature, concentration of chemicals and pressure on equilibrium systems, and consider that these can be predicted by applying Le Chatelier's principle. Students also analyse the quantitative relationship between products and reactants in equilibrium reactions to determine an equilibrium constant. From this calculation, they predict the equilibrium position, either favouring the formation of products or reactants in a chemical reaction. This module also allows students to understand that scientific knowledge enables scientists to offer valid explanations and make reliable predictions. Students make reliable predictions by comparing equilibrium calculations and equilibrium constants to determine whether a combination of two solutions will result in the formation of a precipitate.
Inquiry question: How does solubility relate to chemical equilibrium?
derive equilibrium expressions for saturated solutions in terms of Ksp and calculate the solubility of an ionic substance from its Ksp value
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