Titrations, Equilibrium & Solubility

Titrations

At equivalence, moles of acid equal moles of base ($M_aV_a = M_bV_b$ for 1:1). Halfway there, $[\text{HA}] = [\text{A}^-]$ and $\text{pH} = \text{p}K_a$. The equivalence pH follows the salt: 7.00 for strong + strong, above 7 for a weak acid, below 7 for a weak base. Choose an indicator whose range brackets the equivalence pH; a polyprotic acid shows one equivalence point per ionizable proton.

Equilibrium and Solubility

$K$ omits pure solids and liquids, and $K_p = K_c(RT)^{\Delta n}$. $Q < K$ shifts right and $Q > K$ left. Concentration and pressure move the position; only temperature changes $K$, and catalysts change neither. For a salt, $K_{sp}$ follows stoichiometry ($\text{CaF}_2$: $K_{sp} = 4s^3$), a precipitate forms when $Q_{sp} > K_{sp}$, and a common ion lowers solubility.

Key Takeaways

• Half-equivalence: $\text{pH} = \text{p}K_a$; equivalence is the steepest point.
• Only temperature changes $K$.
• A shared ion makes a salt LESS soluble.