Salts as Acids and Bases

Cations SloshingAnions Sloshing

SaltIonic CompoundDissolvesIons SloshIons as AcidsIons as Bases

Assuming that only one ion affects the pH.

Salts that produce Neutral Solutions• Salts that consist of:

– Cations of strong bases (K+, Na+, etc.)– Anions of strong bases (Cl-, NO3

-, etc.)

EX. KCl, NaCl, NaNO3, KNO3

Turn to p. 657LOOK AT TABLE!

• For any salt whose: – cation has neutral properties (Na+ , K+ , etc)– anion is conjugate base of a weak acid … and Kb can be

calculated

Salts that produce Basic Solutions

• Salts as Weak Bases Example: Calculate the pH of a .3 M NaF solution. The Ka for HF is 7.2 x 10-4.

• For salts in which/that contain:– The anion is not a base– The cation is the conjugate acid of a weak base–Highly charged metal ion (polarizes the O-H

bonds causing H to be more acidic)• The higher the charge of the metal ion, the

stronger the acidity of the hydrated ion

Salts that produce Acidic Solutions

Salts as Weak Acids Examples

• Calculate the pH of 0.10 M NH4Cl solution. The Kb value for ammonia = 1.8 x 10 -5.

• Calculate the pH of 0.10 M AlCl3 solution. The Ka value for Al(H2O)6

+3 = 1.4 x 10 -5.

What if both ions affect pH?Qualitative Comparisons

• Compare Ka of acidic ion to Kb value of basic ion

Ka > Kb ACIDICKa < Kb BASICKa = Kb NEUTRAL

CREATE SUMMARY CHART

• Go here http://www.sciencegeek.net/APchemistry/Presentations/14_Salts/index.html

• Work through examples!