Textbook Question
Calculate the solubility of LaF3 in grams per liter in (a) pure water.
Ch.17 - Additional Aspects of Aqueous Equilibria
Chapter 17, Problem 59
Consider a beaker containing a saturated solution of CaF2 in equilibrium with undissolved CaF2(s). Solid CaCl2 is then added to the solution. (b) Will the concentration of Ca2+ ions in solution increase or decrease? (c) Will the concentration of F- ions in solution increase or decrease?
Verified step by step guidance1
Identify the initial equilibrium condition: The saturated solution of CaF2 is in equilibrium, meaning the rate of dissolution of CaF2(s) is equal to the rate of precipitation. The equilibrium expression is Ksp = [Ca2+][F-]2.
Understand the effect of adding CaCl2: Adding CaCl2 to the solution introduces additional Ca2+ ions because CaCl2 dissociates completely in water to form Ca2+ and Cl- ions.
Apply Le Chatelier's Principle: According to Le Chatelier's Principle, adding more Ca2+ ions will shift the equilibrium to the left to counteract the change, resulting in the precipitation of more CaF2(s).
Determine the change in Ca2+ concentration: Since the equilibrium shifts to the left, the concentration of Ca2+ ions in the solution will decrease as more CaF2 precipitates.
Determine the change in F- concentration: As the equilibrium shifts to the left, the concentration of F- ions will also decrease because they are being used up to form more solid CaF2.
Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Saturation and Solubility Product (Ksp)
A saturated solution is one where the maximum amount of solute has dissolved at a given temperature, and any additional solute will not dissolve. The solubility product constant (Ksp) quantifies the equilibrium between the solid and its ions in solution. For CaF2, Ksp is defined as [Ca2+][F-]^2, indicating the relationship between the concentrations of the ions in a saturated solution.
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Solubility Product Constant
Common Ion Effect
The common ion effect occurs when the addition of an ion that is already present in a solution decreases the solubility of a sparingly soluble salt. In this case, adding CaCl2 introduces more Ca2+ ions into the solution, which shifts the equilibrium of the CaF2 dissolution reaction to the left, reducing the solubility of CaF2 and thus decreasing the concentration of F- ions.
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Le Chatelier's Principle
Le Chatelier's Principle states that if a system at equilibrium is disturbed, the system will adjust to counteract the disturbance and restore a new equilibrium. In this scenario, adding CaCl2 disturbs the equilibrium of the CaF2 dissolution, leading to a decrease in the concentration of F- ions as the system shifts to reduce the effect of the added Ca2+ ions.
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Related Practice
Textbook Question
Calculate the solubility of LaF3 in grams per liter in (b) 0.010 M KF solution.
Textbook Question
Calculate the solubility of LaF3 in grams per liter in (c) 0.050 M LaCl3 solution.
Textbook Question
Consider a beaker containing a saturated solution of CaF2 in equilibrium with undissolved CaF21s2. Solid CaCl2 is then added to the solution. (a) Will the amount of solid CaF2 at the bottom of the beaker increase, decrease, or remain the same?
Textbook Question
Calculate the solubility of Mn(OH)2 in grams per liter when buffered at pH (a) 7.0 (b) 9.5 (c) 11.8.
Textbook Question
Calculate the molar solubility of Ni(OH)2 when buffered at pH (a) 8.0.