1. Salt Hydrolysis

2. Salts Ionic compound made up of CATION and ANION
Has acidic and basic properties
Based on ions produced when salts dissociate
No acid/base properties—group I/II cations
(ex. Na+, Li+, K+, Ca+2)
No basic properties—conjugate bases from monoprotic acids (ex. Cl-, Br-, NO3-)
Ex. NaCl, CaBr2

3. Salt Hydrolysis Acid-base reactions between ions and water
What do we mean by acidic, basic, or neutral salts?
Think about how salt is formed……

4. 1. Salt Formation from Strong Base and Weak Acid
Salt forms a BASIC solution.
Conjugate base ion reacts with water to give hydroxide (OH-) ions.
Ex. Potassium fluoride (KF)
KF  K F-
F- + H2O  HF + OH-

5. 2. Salt Formation from a Strong Acid and Weak Base
Salt forms an ACIDIC solution
Conjugate acid reactions with water to give hydronium ion (H3O+)
Ex. Ammonium nitrate (NH4NO3)

6. 3. Salt Formation from Strong Acid and Strong Base
Salt forms a NEUTRAL solution
Conjugate base resulting from salt dissociation is weak
Ex. Sodium chloride (NaCl)

7. Example 1:
Calculate the concentration of HOAc, OAc- and OH- at equilibrium in a 0.10M NaOAc solution (Ka for HOAc = 1.8 x 10-5).
[OAc] = 0.10M
[HOAc] = 7.5x10-6
[OH] = 7.5 x 10-6

8. Types of Acid-Base Reactions
Strong Acid/Strong Base
Weak Acid/Strong Base
Strong Acid/Weak Base
Weak Base/Weak Acid

9. 1) Strong Acid/Strong Base
Reaction goes to completion, K = 1x1014, pH = 7
H3O+ + OH-  H2O(l) + H2O(l)
Always this net ionic equation
H+ and OH- form H2O

10. Example 2: HCl + NaOH 

11. 2) Weak Acid/Strong Base
Produces H2O and the conjugate base from weak acid
Reaction goes MOSTLY to completion
Solution’s pH is more dependent on CONJUGATE Base (A- )’s reaction with water
Find equilibrium constant (K) by combining known dissociation reactions to get the correct overall equation and solve for K

12. Example 3: HNO2 + OH- H2O + NO2-
HNO2 + H2O(l)  H3O+ + NO2- Ka = 5.1 x 10-4
H3O OH-  2H2O(l) K = 1 x 1014

13. 3. Strong Acid/Weak Base
Weak bases tend to contain nitrogen-based compounds such as NH3
Weak bases accept protons from acid
Combine known dissociation reactions to get the correct overall equation and solve for K

14. Example 4: CH3NH2 + H3O+ CH3NH3+ + H2O(l)
CH3NH2 + H2O  CH3NH OH- Kb = 4.8x10-4
H3O+ + OH-  2H2O K = 1.0x1014

15. 4) Weak Base/Weak Acid
Reaction direction is dependent on equilibrium constant value.
Most reactions do NOT go to completion
Use this format and find Ka and Kb values for acid and base dissociations.
HA + H2O(l)  H3O+ + A Ka
B + H2O(l)  BH+ + OH Kb
H3O+ + OH-  2H2O(l) K = 1.0 x 1014

16. Example 5: CH3NH2 + HNO2  CH3NH2+ + NO2-
Krxn = (Ka) (Kb)(1x1014) = 2.5x107

17. Homework
pp. 670 #63-64, 67-70