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).
8. Types of Acid-Base Reactions
1) Strong Acid/Strong Base
2) Weak Acid/Strong Base
3) Strong Acid/Weak Base
4) 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
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
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