Lecture 12

Conjugate acid/base pairs

HA + B A- + BH+

Salts Ionic solid

Product of acid/ base reactionneutralization

Autoprotolysis of water H2O + H2O H3O+ + OH-

Kw = [OH-][H3O+]= 1.01 x 10-14 @ 25o C

What is pH? pH = -log{H3O+} ~ -log[H3O+]

pH of pure water?

Acidic vs. Bases

Strength of Acids/Bases

Strength of Acids/Bases

Weak Acid : Doesn’t completely dissociates

]HA[

]A][H[K

AHHA

a

Ka

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

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

Polyprotic acids

Ionic Strength

C = molarity z = charge

1:1 electrolytes (NaCl) - μ = molarity 2:1, etc electrolytes (BaCl2) - μ > molarity

i

2iizC2

1μ

i

2iizC2

1μ

What is the ionic strength of 0.1 M LiCl?

What is the ionic strength of 0.1M Ca(NO3)2?

Electrolyte (salt) effect

Effective concentration of ions become less as μ increases

Shielding effect

Non-ideal behavior

Activity

[i]o = 1M (makes {i} dimensionless) γ is activity coefficient

oi[i]

[i] γ a{i}

nY

mX

'spsp

nY

mX

nmsp

nY

mXsp

nm

γγKK

γγ]Y[]X[K

aaK

nYmXYX

Extended Debye-Hückel equation

C25 at )305μα(1

μz51.0γlog o

2

α – ion size

z - charge

γ – activity coefficient

μ – ionic strength

Interpolate

Δx

unknown x

Δy

unknown y