Salts and pH

Soluble salts dissociate in water to produce ions. Salts are basically ionic compounds that can be formed from the reaction from an acid and a base. Not all aqueous salt solutions are neutral; their pH depends on how the cation and anion interact with water. This interaction is called hydrolysis.

Neutral salts Salts from strong acids and strong bases are NEUTRAL Example: NaCl from NaOH and HCl LiCl from LiOH and HCl

Basic salts Cations from strong base and anions from weak acid have a strong conjugate base. This interacts with water by gaining a proton and generating hydroxide ions. A - + H 2 O ↔ HA + OH - Salts from STONG bases and WEAK acids are BASIC Example: NaC 2 H 3 O 2 from NaOH and HC 2 H 3 O 2 C 2 H 3 O H 3 O + ↔ OH - + HC 2 H 3 O 2

Acidic Salts Cations from WEAK base and anions from STRONG acid have a strong conjugate acid. This interacts with water by gaining a proton and generating hydronium ions. HB + + H 2 O ↔ B + H 3 O + Salts from WEAK base and STRONG acid are ACIDIC Example: NH 4 Clfrom NH 4 OH and HCl NH H 2 O ↔ NH 3 + OH -

Cations from weak base and anions from weak acid have both strong conjugates. Since both can interact with water, the resulting pH depends upon the respective strength of the conjugate acid or base. If K a > K b then salt is acid If K a < K b then salt is base If K a = K b then salt is neutral

NaNO 3 NaOH + HNO₃  NaNO 3 + H₂O strong base + strong acid  neutral salt + water CH 3 NH 3 CN CH₃NH₂ + HCN   CH 3 NH 3 CN + H₂O weak base + weak acid  salt + water have to check whether Ka or Kb is bigger to determine if the salt is acidic or basic. Would the following salts be acidic, basic or neutral? Support with hydrolysis when appropriate.

What is the pH of a 0.10 M solution of sodium acetate?

What is the pH of a 0.10 M solution of ammonium nitrate?