Quick questions on Solubility equilibria and Ksp: TCE Chemistry (Tasmania)

When an ionic solid is only slightly soluble, a saturated solution reaches equilibrium with the undissolved solid:

Molar solubility $s$ is the moles of salt that dissolve per litre to give a saturated solution. From the dissolution equation, write each ion concentration in terms of $s$, then substitute into the $K_{sp}$ expression. The coefficients matter: for a $1:1$ salt $K_{sp} = s^2$, but for a $1:2$ salt $K_{sp} = 4s^3$.

Solubility depends on temperature: most ionic solids dissolve more readily as temperature rises, so $K_{sp}$ values are quoted at a stated temperature (usually $25\ ^\circ\text{C}$). The common ion effect lowers solubility when a shared ion is already present. Solubility can also change with pH when the anion is basic: a salt such as calcium carbonate dissolves more in acidic solution because $\text{H}^+$ removes carbonate ions (as $\text{CO}_2$ and water), pulling the dissolution equilibrium to the right. This is the chemistry behind acid attack on limestone and the formation of caves.