lec18 - + donation : H 3 A Three equilibria : k a1 , k a2 ,...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
1 Last Time • Dilute solutions – autoprotolysis –[H 3 O + ] ~ 10 –6 –10 –7 • Strong acids and bases – know this • Weak acids and bases – be aware of Charge Balance • Total charge in the solution must be zero!! • For acids : [H 3 O + ] = [A ] + [OH ] K w = [H 3 O + ][OH ] = [H 3 O + ] ( [H 3 O + ] – [HA] ) • For bases : [OH ] = [H 3 O + ] + [M + ] K w = [H 3 O + ][OH ] = [H 3 O + ] ( [H 3 O + ] + [B ] ) Example • What is the pH of a 5.6 x 10 –8 M solution of HCl? Dilute Solutions – Weak Acids • Problem: Acid with K a and [H 3 O + ] ~ 10 –7 • Wrong answer: use “x” and find pH directly • Correct answer – solve for [H 3 O + ] using K w = [H 3 O + ][OH ] K a = [H 3 O + ] = [OH ] + [A ] A = [HA] + [A ] [H 3 O + ][A ] [HA]
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
2 Example What is the pH of a 1 x 10 –6 M solution of phenol in water given that K a for phenol is 1.3 x 10 –10 ? Polyprotic Acids • Monoprotic – one H + donation : HA • Diprotic – two H + donation : H 2 A – Two equilibria : k a1 , k a2 – Example: H 2 S • Triprotic – three H
Background image of page 2
Background image of page 3
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: + donation : H 3 A Three equilibria : k a1 , k a2 , k a3 Example : H 3 PO 4 Diprotic Acids H 2 A(aq) + H 2 O(l) H 3 O + (aq) + HA (aq) K a1 HA (aq) + H 2 O(l) H 3 O + (aq) + A 2 (aq) K a2 H 2 A H 3 O + HA A 2 [Initial] a 0 0 [Change] x +x+y +xy +y [Equilib.] ax +x+y +xy +y Double Equilibrium Two equations two unknowns K a1 = K a2 = Can simplify when K a2 << K a1 Use weak acid approach and proceed stepwise. x 2 y 2 a x y (x + y) x y 3 Example Calculate the pH of a 0.1 M solution of H 2 S given that K a1 = 1.3 x 10 7 and K a2 = 7.1 x 10 15 . Example Calculate the concentration of all components of a 0.01 M H 3 PO 4 solution given that K a1 = 7.6 x 10 3 , K a2 = 6.2 x 10 8 , and K a3 = 2.1 x 10 13 ....
View Full Document

This note was uploaded on 04/23/2008 for the course CHEM 2B taught by Professor Clemens during the Winter '08 term at UC Davis.

Page1 / 3

lec18 - + donation : H 3 A Three equilibria : k a1 , k a2 ,...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online