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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 pHSimple 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…