IV.13. HYDROLYSIS (Hebden p. 144 – 148)
Hydrolysis of a Salt Rx between water and cation &/or anion in salt that produces an acidic or basic solution All salts are 100% ionized in water
Spectator Ions Do NOT react with water The conjugates of STRONG acids and bases
Spectator Cations Alkali metals Alkaline earth metals Ex: NaOH Na+ + OH-
Spectator Anions 1st 5 @ top of Acid/ Base Table (not HSO4- b/c it is a weak acid) Ex: HCl H+ + Cl-
To determine the behavior of salt in water… Determine ions Discard spectators Remaining ions are acids if on acid side of table or bases if on base side of table
Ex #1: NaCl Na+ + Cl- Both Na+ and Cl- are spectators Therefore, solution is NEUTRAL
2. NH4Cl NH4+ + Cl- Cl- is a spectator Solution is acidic NH4+ + H2O = H3O+ + NH3
3. NaF Na+ + F- Na+ is a spectator Solution is basic F- + H20 = HF + OH-
4. NaHC2O4 Na++HC2O4- Na+ is a spectator Solution either acidic or basic b/c HC2O4- is amphiprotic We must determine which rx is predominant
Ka for HC2O4- = 6.4 x 10-5 Kb = Kw /Ka = 1.00 x 10-14 / 5.9 x 10-2 = 1.7 x 10-13 Ka > Kb so solution is acidic HC2O4- + H20 = H3O+ +C2O42-
Must determine predominant rx 5. NH4NO2 NH4+ + NO2- No spectators Must determine predominant rx
Ka of NH4+ = 5.6 x 10-10 Kb of NO2- = Kw/Ka = 1.0 x 10-14 / 4.6 x 10-4 = 2.2 x 10-11 Solution is acidic NH4+ + H20 = H3O+ + NH3