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?

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Identify the relevant chemical reactions and solubility products. For CaF2, the dissolution can be represented as: CaF2(s) ⇌ Ca2+(aq) + 2F-(aq).

Recognize that the addition of CaCl2 introduces more Ca2+ ions into the solution, as CaCl2 dissociates completely into Ca2+ and Cl- ions: CaCl2(s) → Ca2+(aq) + 2Cl-(aq).

Understand the effect of increased Ca2+ concentration on the equilibrium of the CaF2 dissolution. According to Le Chatelier's Principle, adding more of a product (Ca2+) will shift the equilibrium to the left, favoring the formation of the solid (precipitate).

Predict the effect on the solubility of CaF2. With the equilibrium shifting left, the solubility of CaF2 will decrease, leading to the formation of more solid CaF2 at the bottom of the beaker.

Conclude that the amount of solid CaF2 at the bottom of the beaker will increase as a result of adding solid CaCl2.

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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 [Ca^2+][F^-]^2, and changes in ion concentration can shift this equilibrium.

Common Ion Effect

The common ion effect occurs when the addition of an ion common to a saturated solution decreases the solubility of the solute. In this case, adding CaCl2 introduces Ca^2+ ions into the solution, which can shift the equilibrium of CaF2 dissolution, potentially leading to a decrease in the amount of solid CaF2 present.

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 the context of the CaF2 solution, adding CaCl2 alters the concentration of Ca^2+ ions, prompting the system to shift towards the formation of more solid CaF2 to re-establish equilibrium.