Acid-Base Properties of Salt Solutions

1
Acid-Base Properties of Salt Solutions

• Salts are solids at room temperature composed of
  cations and anions arranged in a crystal lattice
  (i.e. ionic compounds).
• When salts dissolve in water, they dissociate
  into aqueous solutions of ions that may or may
  not affect the pH of a solution.

2
Salts that Form Neutral Solutions

• Salts with the cation of a strong base and the
  anion of a strong acid. (eg NaCl, K2SO4)

3
Salts that Form Acidic Solutions

• Salts where the cation is the conjugate acid of a
  weak base and the anion of a strong acid. (eg
  NH4Cl)
• Non-metal oxides (eg CO2)
• Salts where the cation is a highly charged metal
  ion and the anion is from a strong acid. (eg
  AlCl3)

4
Salts that Form Basic Solutions

• Salts with the cation of strong base and the
  anion of a weak acid. (eg NaC2H3O2)
• Metal oxides (eg CuO)

5
Special Cases

• The pH of a salt where the cation is the
  conjugate acid of a weak base and the anion is
  the conjugate base of the weak acid will depend
  on the Ka value of the conjugate acid and the Kb
  value of the conjugate base.
• If Kagt Kb, pH will be acidic
• Kalt Kb, pH will be basic
• Ka Kb, pH will be neutral

6
Summary and Homework

• Steps for predicting the Acid-Base Behaviour of a
  salt page 585
• Summary Chart page 592
• Page 588 1-5