lecture 12. conjugate acid/base pairs ha + b a - + bh +
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Lecture 12
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Conjugate acid/base pairs
HA + B A- + BH+
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Salts Ionic solid
Product of acid/ base reactionneutralization
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Autoprotolysis of water H2O + H2O H3O+ + OH-
Kw = [OH-][H3O+]= 1.01 x 10-14 @ 25o C
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What is pH? pH = -log{H3O+} ~ -log[H3O+]
pH of pure water?
Acidic vs. Bases
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Strength of Acids/Bases
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Strength of Acids/Bases
Weak Acid : Doesn’t completely dissociates
]HA[
]A][H[K
AHHA
a
Ka
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Strength of Acids/Bases Weak Base: Doesn’t completely dissociates
]B[
]OH][BH[K
OHBH0HB
b
K2
b
]A[
]OH][HA[K
OHHAOH A
b
K2
a
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Relationship between Ka and Kb
baw
w2
bK
2
aK
KKK
] ][OH[HK OHHOH
][A
][HA][OH K OHHAOH A
[HA]
]][A[H K AHHA
b
a
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Polyprotic acids
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Ionic Strength
C = molarity z = charge
1:1 electrolytes (NaCl) - μ = molarity 2:1, etc electrolytes (BaCl2) - μ > molarity
i
2iizC2
1μ
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i
2iizC2
1μ
What is the ionic strength of 0.1 M LiCl?
What is the ionic strength of 0.1M Ca(NO3)2?
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Electrolyte (salt) effect
Effective concentration of ions become less as μ increases
Shielding effect
Non-ideal behavior
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Activity
[i]o = 1M (makes {i} dimensionless) γ is activity coefficient
oi[i]
[i] γ a{i}
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nY
mX
'spsp
nY
mX
nmsp
nY
mXsp
nm
γγKK
γγ]Y[]X[K
aaK
nYmXYX
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Extended Debye-Hückel equation
C25 at )305μα(1
μz51.0γlog o
2
α – ion size
z - charge
γ – activity coefficient
μ – ionic strength
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Interpolate
Δx
unknown x
Δy
unknown y