Chapter 14
Acids and Bases
AP*
Section 14.6Bases
Arrhenius bases: Brønsted–Lowry bases: The pH of a basic solution: Ionic compounds containing ____ are generally
considered strong bases. LiOH, NaOH, KOH, Ca(OH)2
Also useful: pOH = –log[OH–] pH = 14.00 – pOH KaKb = Kw & Kw = 1×10-14
2
produce OH– ions.are proton acceptors
>7OH-
Section 14.6Bases
Calculate the pH of a 1.0 × 10–3 M solution of sodium hydroxide.pOH = -log(1.0 × 10–3)pOH = 3.00pH = 14 – pOHpH = 14 - 3
pH = 11.00Two significant figures!!
Copyright © Cengage Learning. All rights reserved 3
CONCEPT CHECK!CONCEPT CHECK!
Section 14.6Bases
Calculate the pH of a 1.0 × 10–3 M solution of calcium hydroxide.Calcium hydroxide = Ca(OH)2
1.0 × 10–3 M Ca(OH)2 , so…
[Ca2+] = 1.0 × 10–3 M[OH-] = 2.0 × 10–3 M pOH = -log(2.0 × 10–3)pOH = 2.699pH = 14 – pOHpH = 14 – 2.699
pH = 11.30
4
Section 14.6Bases
Comparing Ka to Kb.
HCN(aq) + H2O(l) CN–(aq) + H3O+(aq); Ka = 6.2 × 10–10
CN–(aq) + H2O(l) HCN(aq) + OH–(aq) ; Kb =
Kb = Kw ÷Ka = 1×10-14 ÷ 6.2 × 10–10 = 1.6 × 10–5
Copyright © Cengage Learning. All rights reserved 5
][]][[
CNOHHCNKb
][]][[ 3
HCNOHCNKa
x
Wba KOHHKK ]][[
Section 14.6Bases
Calculate the pH of a 2.0 M solution of ammonia (NH3).
(Kb = 1.8 × 10–5)
pH = 11.78
Copyright © Cengage Learning. All rights reserved 6
CONCEPT CHECK!CONCEPT CHECK!
Section 14.7Polyprotic Acids
Acids that can furnish more than one proton. Always dissociates in a stepwise manner, one proton at a
time. The conjugate base of the first dissociation equilibrium
becomes the acid in the second step. For a typical weak polyprotic acid:
Ka1 > Ka2 > Ka3
For a typical polyprotic acid in water, only the first dissociation step is important to pH.
Copyright © Cengage Learning. All rights reserved 7
Section 14.7Polyprotic Acids
Calculate the pH of a 1.00 M solution of H3PO4.
Ka1 = 7.5 × 10-3
Ka2 = 6.2 × 10-8
Ka3 = 4.8 × 10-13
pH = 1.06Copyright © Cengage Learning. All rights reserved 8
EXERCISE!EXERCISE!
Section 14.7Polyprotic Acids
Calculate the equilibrium concentration of PO43- in a
1.00 M solution of H3PO4.
Ka1 = 7.5 × 10-3
Ka2 = 6.2 × 10-8
Ka3 = 4.8 × 10-13
[PO43-] = 3.6 × 10-19 M
Copyright © Cengage Learning. All rights reserved 9