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+ +C2O4

2-

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