Nature of Salts Green & Damjii – Chapter 8 – Section 18.3 Chang - Chapter 15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Acid-Base Properties of Salts Salts forming Neutral Solutions: Salts containing an alkali metal or alkaline earth metal ion (except Be 2+ ) and the conjugate base of a strong acid (e.g. Cl -, Br -, and NO 3 - ). NaCl (s) Na + (aq) + Cl - (aq) H2OH2O Salt – any compound containing both positive and negative ions. We think of these as electrically neutral, but they may form neutral, acidic or basic solutions when added to water.

Acid-Base Properties of Salts Basic Solutions: Salts derived from a strong base and a weak acid. NaCH 3 COOH (s) Na + (aq) + CH 3 COO - (aq) H2OH2O CH 3 COO - (aq) + H 2 O (l) CH 3 COOH (aq) + OH - (aq) This salt produces OH - (aq), making the pH basic.

Acid-Base Properties of Salts Acid Solutions: Salts derived from a strong acid and a weak base. NH 4 Cl (s) NH 4 + (aq) + Cl - (aq) H2OH2O NH 4 + (aq) + H 2 O (l) NH 3 (aq) + H 3 O + (aq) This salt produces H 3 O + (aq), making the pH acidic.

Acid-Base Properties of Salts Acid Solutions: Salts with small, highly charged metal cations (e.g. Al 3+, Cr 3+, Fe 3+, and Be 2+ ) and the conjugate base of a strong acid. Ex: AlCl 3 Al(H 2 O) 6 (aq) Al(OH)(H 2 O) 5 (aq) + H + (aq) AlCl 3 (s) Al 3+ (aq) + 3 Cl - (aq) H2OH2O Al 3+ (aq) Al(H 2 O) 6 (aq) H2OH2O

Try these out… predict the acid/base nature of these salts… ammonium nitrate iron(III) chloride sodium sulfate potassium acetate

Acid-Base Properties of Salts Solutions in which both the cation and the anion hydrolyze: K b for the anion > K a for the cation, solution will be basic K b for the anion < K a for the cation, solution will be acidic K b for the anion  K a for the cation, solution will be neutral Sometimes it is challenging to make a decision… and there are patterns… these typically don’t show up on IB exams… so don’t worry about these.

15.10

A related trip down memory lane… What happens to the pH of water when you add a metal oxide to it? What happens to the pH of water when you add a nonmetal oxide to it?

What happens to the pH of water when you add a metal oxide to it? What happens to the pH of water when you add a nonmetal oxide to it? CO 2 (g) + H 2 O (l) H 2 CO 3 (aq) N 2 O 5 (g) + H 2 O (l) 2HNO 3 (aq) Na 2 O (s) + H 2 O (l) 2 Na + (aq) + 2 OH - (aq)

Oxides of the Representative Elements In Their Highest Oxidation States 15.11

Textwork Read Section 18.3 – Salt Hydrolysis pp Do Ex 18.3 # 1-4