What is the effect on the amount of CaHPO that dissolves and...

What is the effect on the amount of CaHPO_ that dissolves and the concentrations of $\mathrm{Ca}^{2+}$ and $\mathrm{HPO}_{4}^{-}$ when each of the following are added to a mixture of solid CaHPO $_{4}$ and water at equilibrium? (a) $\mathrm{CaCl}_{2}$ (b) $\mathrm{HCl}$ (c) $\mathrm{KClO}_{4}$ (d) $\mathrm{NaOH}$ (e) CaHPO_ $_{4}$

What is the effect on the amount of CaHPO_ that dissolves and the concentrations of $\mathrm{Ca}^{2+}$ and $\mathrm{HPO}_{4}^{-}$ when each of the following are added to a mixture of solid CaHPO $_{4}$ and water at equilibrium?
(a) $\mathrm{CaCl}_{2}$
(b) $\mathrm{HCl}$
(c) $\mathrm{KClO}_{4}$
(d) $\mathrm{NaOH}$
(e) CaHPO_ $_{4}$

Key Concepts

Ionic Strength and Inert Ion Effects

Ionic strength refers to the overall concentration of ions in solution and can affect the activity coefficients of the ions involved in an equilibrium. The addition of inert salts, which do not react chemically with the species in the equilibrium, can still alter the solubility by modifying the ionic atmosphere, although the effects are generally less significant than those caused by changes in the concentration of a common ion or pH adjustment.

Acid?Base Effects on Equilibrium

Acid–base reactions can alter solubility equilibria when an ion from the salt reacts with added protons or hydroxide ions. For example, if an ion from the salt behaves as a weak base or conjugate base, adding acid can protonate the ion and remove it from the equilibrium, thereby shifting the dissolution balance and potentially increasing solubility.

Solubility Equilibrium

Solubility equilibrium refers to the dynamic balance established between a sparingly soluble solid and its dissociated ions in solution. In such equilibria, the solubility product constant (Ksp) quantifies the product of the molar concentrations of the dissolved ions raised to the power of their stoichiometric coefficients, and any disturbance to the equilibrium conditions can shift the balance according to Le Chatelier’s principle.

Le Chatelier’s Principle

Le Chatelier’s principle states that when a system at equilibrium is disturbed by a change in concentration, temperature, pressure, or pH, the equilibrium will shift in a direction that counteracts the change. In solubility equilibria, this principle helps to predict how the addition of species (such as common ions or acids/bases) will shift the dissolution balance of a solid salt.

Common Ion Effect

The common ion effect occurs when an ion that is a constituent of a dissolved salt is added from another source, causing a shift in the equilibrium to reduce the solubility of the salt. In the context of a sparingly soluble salt, increasing the concentration of one of the ions typically drives the equilibrium toward the undissolved solid, thereby reducing both its solubility and the concentrations of the dissolved ions.

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