Outline: 2/26/07

Today: Start Chapter 17

CAPA 10 & 11 – due today Pick up CAPA 12 & 13 – outside Turn in seminar reports – to me

Acid-base Equilibria: Acid & Bases: definitions Defining/Calculating pH

Simple pH Calculations from Ka

Any questions on equilibria?

Lots of suggested problems to do….16.1, 16.9, 16.11, 16.17, 16.19, 16.21, 16.1, 16.9, 16.11, 16.17, 16.19, 16.21, 16.23, 16.25, 16.27, 16.29, 16.31, 16.33, 16.23, 16.25, 16.27, 16.29, 16.31, 16.33, 16.35, 16.37, 16.43, 16.45, 16.47, 16.49, 16.35, 16.37, 16.43, 16.45, 16.47, 16.49, 16.51, 16.57, 16.59, 16.63. 16.65, 16.67, 16.51, 16.57, 16.59, 16.63. 16.65, 16.67, 16.69, 16.71, 16.73, 16.75, 16.79, 16.8116.69, 16.71, 16.73, 16.75, 16.79, 16.81

Quiz #5

Please put books/papers away…

Remember: lots of partial credit for Remember: lots of partial credit for setting up the problem correctly…setting up the problem correctly…

Solving it just gets you the last pointsSolving it just gets you the last points

Quiz #5

Please turn your quizzes over and pass them to your right…

Acids & Bases: These are all examples of equilibria

big Keq = strong acid (dissociation) little Keq = weak acid

HSO3 + H2O H3O+ + SO3

Keq = 1000+ HCl + H2O H3O+ + Cl

Keq = 6.4 10

Chapter 17: More Equilibrium!What exactly is in an aqueous solution?

HNO3

H3O+

H2O

NO3

p. 140

Does this differ from a weak acid?

HOAcH2O

p. 141

A combination of previous chapters: Solubility rules: Highly soluble: ionic salts of Cl, Br, I, ionic salts of NO3

, SO4,

ionic salts of ClO4, etc.

Equilibrium rules: Keq = [products]/[reactants] Big Keq large extent of reaction

= Strong Acids

= Strong Acids

Just a few strong acids & bases, the

rest are weak:

The extent of dissociation:Ka and Kb Define acid dissociation constant: Ka = [H+][A]/[ HA] Define base dissociation constant: Kb = [B+][OH]/[BOH]

Called water dissociation constant or “autoionization”

= 1 1014 (by definition)

OK, what exactly is water anyway? H2O + H2O H3O+ + OH Keq = [H3O+][OH] = Kw

Define water as neutral…. Kw = 10(arbitrary scale definition) then: [H3O+] = [OH] = x or: x2 = 10or x = 10

What’s the pH of neutral water? = log(10

Define pH = log [H+]

Same thing for bases…. Define pOH = log(OH)

Since Kw = [H3O+][OH] = 10

log[H3O+] + log[OH] = log (10) or pH + pOH = 14 None of this is really new….using acids

and bases in lab all year! e.g. pHydron paper, pH electrodes, Concentration vs. strength!

Calculation Examples: Calculate the pH of a solution of

2.5102 M HClO4? (perchloric acid) Step #1: identify the acid If strong acid complete

dissociation

Step #2: pH = log [H+] log (2.5102) = 1.60

HClO4H+ +

ClO4

2.5102 M 0 0 init 0 equil 2.5102 M 2.5102

M

Examples: Calculate the pH of a solution of

2.5102 M HClO? (hypochlorous acid) Step #1: identify the acid if weak acid look up Ka = 3.5 108

Step #2: pH = log [H+] log (2.7105) = 4.56

HClO H+ + ClO

2.5102 M 0 0 init (2.5102x)M x M x M equil

Weak Base Example: Calculate the pH of a solution of

2.5102 M trimethylamine (CH3)3N ? Step #1: identify it as a weak base look up Kb = 6.5 105

(CH3)3N H2OOH + (CH3)3N H+

2.5102 M 0 0 init

(2.5102x)M x M x M equil Step #2: pOH = log [OH] log (1.3103) = 2.89 Step #3: 14 pOH = pH = 11.11

Problem solving overview: Skills needed to solve these problems: 1) Identify strong/weak acid/bases

2) Identify conjugate acid/bases & salts

3) Solving equilibrium problems

4) Identifying & making the correct Keq

Know the 6 strong acids / 4 strong bases…

Know solubility rules & acid/base definitions

Solve for x…forward or backwards...

Add equations to make new one & K’s multiply

And Practice, Practice, Practice…