ACID BASE CHEMISTRY

TERMS, ETC.

AMPHOTERIC:Subst. acts as either an acid or a base

Proton (Acidic p+): H+ ion; the acidic hydrogen(s) present in an acid

HNO3: one H+ H2SO4: two H+H3PO4: three H+

MONOPROTIC ACID: An acid w/ one H+

DIPROTIC ACID: An acid w/ two H+

POLYPROTIC ACID: An acid w/ 3 or more H+

HYDRONIUM ION:

H2O (l) + H+1 (aq) ---------> H3O+1 (aq)

Proton:H+; a hydrogen w/ characteristics like a proton itself -----1 p+, 0 n0, 0 e-

Acid BASE

All acids contain H+; when in water givesolution higher [H+]

All bases contain OH-;when in water givesolution higher [OH-]

Arrhenius

BRONSTAD – LOWRY

Acid

Any subst. thatdonates a proton; H+

BASE

Any subst. thataccepts a proton; H+

LEWIS Any subst. thataccepts an e- pair

Any subst. thatdonates an e- pair

ACIDS BASES

•Taste sour•Turns litmus blue -- red•Lowers pH

•Feels slippery•Turns litmus red -- blue•Increases pH

The stronger the acid the better it is at donating H+

STRONG ACIDSSTRONG ACIDS

HCl ; HBr ; HI ; HNO3 ; H2SO4 ; HClO4H+

+Cl-H++I- 2H++SO4

-

2

0 7 14

pH SCALE

STRONG ACIDIC

STRONG BASIC

MILDACIDIC

MILDBASIC

WEAK ACIDIC

WEAK BASIC

NEUTRAL ( )

Kw: constant for water, 1*10-14

ACID-BASE REACTIONS

HCl (aq) + KOH (aq) ---> KCl (aq) + HOH (l) acid base salt water

pH -- pOH -- [H+] -- [OH-] CALCULATIONS

Formulas to Use

-w OH H K

pOH pH pK w

Constants

Kw = 1 *10 –14

pH = -log [H+]

pOH = -log [OH-]

pKw = 14

Rules for LOGSLog 1 = 0

Log 10exp = exponent

[H+] = 1*10-pH

[OH-] = 1*10-pOH

Rules for LOGS

DIVISION

MULTILPLY84.6 Log5.8 Log 84.65.8Log

32.4 Log12.6 Log 32.412.6Log

Calculate pH for thefollowing solutions

1) [H+] = 1 * 10-9

2) [H+] = 0.001

pH = -log (1*10-9) = -(-9) = 9

0.001 = 1*10-3

pH = -log (1*10-3) = -(-3) = 3

3) [H+] = 3.6 * 10-2

pH = -log(3.6*10-2) = 1.44

OR-log 10-2 = 2 pH = 2 – log (3.6) = 2 – 0.56 = 1.44

Find pH & pOH

pOH pKw = pH + pOH 14 = 1.44 + pOHpOH = 14 – 1.44 = 12.56

OR

HK OH- w

2

14

10*6.310*1

= 2.78*10-13

pOH = 13 – log 2.78 = 13 – 0.44 =

If [H+] is 6.7*10-9 mol/L, what is the pH? ACIDIC, BASIC, NEUTRAL

What is the [OH-]? What is the pOH?

pH = -log(6.7*10-9) = 9 – log 6.7 = 9 – 0.83 = 8.17 BASIC

pOH = 14 – 8.17 = 5.83

[OH-] = 1*10-5.83

Find pH Find pOH

Find [OH-]

OR

= 1.49*10-6

CONJUGATE ACID-BASE PAIRS

Acid, loses H+, form conjugate base

Base, gains H+, forms conjugate acid

)(

-1

42(aq)3)(

-2

4)(

1

4 POH NH HPO NH aqaqaq

acid1 acid2base2 base1

CONJUGATE ACID-BASE PAIRS

(aq)3)(

1

4 NH NH

aq )(

-1

42)(

-2

4 POHHPO aqaq

TITRATIONS

Strong Acid + Strong Base ------ Neutral

Strong Acid + Weak Base --- Acidic

Weak Acid + Strong Base --- Basic

Weak Acid + Weak Base ---- ???????

+/- ions of acid not react w/ H2O

“+” ion of strong acid reacts w/ H2O, produces H3O+

“-” ion of strong base reacts to produce OH- ions

Both +/- ions react w/ H2O

STRENGTH

Strong Acid/Base ionize completely equilibrium lies far to the right HCl ------> H+ + Cl-

NaOH -----> Na+ + OH-

Weak Acid slightly ionize equilibrium lies far to the leftHC2H3O2 + H2O <-----> H+ + C2H3O2

-

]OH[HC

]OHC][OH[KO]H[K

O]H][OH[HC

]OHC][OH[K

232

-

2323a2eq

2232

-

2323eq

Ka: acid dissociation constantKb: base dissociation constant

IONIZATION CONSTANTS

Ka acetic acid = 1.8*10-5

Ka nitrous acid = 4.4*10-4nitrous acid more ionized in soln

BASE

NH3 + H2O <---> NH4+ +OH-

][NH

]OH][NH[KO]H[K

O]H][[NH

]OH][NH[K

3

-

4b2eq

23

-

4eq

Kb ammonia = 1.8*10-5

Find the Missing Part ???

CN-1

H2O

SO4-2

HC2H3O2

HC2O4-1

NH4+1

S.A.S.A. yields weak conjugate baseW.A.W.A. yields strong conj. base

MONOPROTIC ACIDS pg. 300

Ka Acid

1.2*10-2 HSO4-

1.2*10-2 HClO2

7.2*10-4 HF

1.8*10-5 HC2H3O2

3.5*10-8 HOCl

5.6*10-10 NH4+

8.3*10-13 SO4-2

8.3*10-13 ClO2-

1.4*10-11 F-

5.56*10-10 C2H3O2-

2.9*10-7 OCl-

1.8*10-5 NH3

Kb Conj. Base

Very Strong Very Weak

Strong

Weak

Weak

Strong

Very Weak Very Strong

Diprotic & Triprotic Acids

H2CO3: 2 acidic protons Ka values for each H+

H CO HCO

H HCO COH2-

3

-

3

-

332Ka1 = 4.3*10-7

Ka2 = 5.6*10-11

typically weak polyprotic acid Ka1 > Ka2 > Ka3

means???? -each step of dissociation is successively weaker-loss of 2nd & 3rd proton occurs less readily

Why???? should not be surprising think in terms of charges, +/- being attracted

S.A. : Ka 10-1 --- 10-3

W.A.: Ka 10-4 & smaller

Polyprotic acid: Ka value lowers w/ each H+ lost Loss of each additional H+ more difficult

H3PO4 + H2O <-----> H3O+ + H2PO4- Ka1

H2PO4- + H2O <-----> H3O+ + HPO4

-2 Ka2

HPO4-2 + H2O <-----> H3O+ + PO4

-3 Ka3

Ka1 > Ka2 > Ka3

10-3 10-8 10-

13

S.B.: Kb????

Ka: acid dissociation constant

HA + H2O <-----> H3O+ + A-

HA

AOH K

-

3

a

HNO3 + H2O <-----> H3O+ + NO3-

3

-

33

aHNO

NOOH K

BUFFER-used to control pH level of a soln.-either remove H+ or add OH- ions-usually W.A. & conj. Base

TITRATIONS.A. + W.B. -------> AcidicW.A. + S.B. -------> BasicS.A. + S.B. -------> NeutralW.A. + W.B. -----> ?? more info.

S.A. ------> weak conjugate BaseW.A. -----> strong conj. Base

Various Ways to Describe Acid Strength

Property S.A. W.A.

Ka value Ka is large Ka is small

Position of dissociation equilibrium

Far to right Far to left

Equilibrium [H+] compared to [HA]o

[H+] [HA]o [H+]<<[HA]o

Strength of conj.base compared to H2O

A- much weaker acid than H2O

A- much stronger base than H2O

INTERMOLECULAR FORCES

Forces that act between diff. molecules

Gases: <<< forces, act independently of each other

Liquids/Solids: >>>> Forces

KEY PTS.

Stronger the Force -------- more difficult to separate atoms/molecules

---- higher melting/boiling pts of subst.

3 MAJOR FORCES

Dipole-DipoleDipole-Dipole London DispersionLondon Dispersion

Polar Cov. Bonds “net polarity”

Weak Force

+/- ends of molecules align together

Dipole-Dipole London Dispersion Hydrogen Bonding

All molecules; behavior due to e- movement w/i subst.

Nonpolar molecules form temporary Polarity

Weak Force; as mole.wt.

Surface Area: > S.A. ---- > Force stronger the molecule held together

Hydrogen BondingHydrogen Bonding

Strong bond Force

H bonded to an O, N, or F of one molecule; that H will be attracted to unsharede- pair of O, N, or F of another molecule

O

H H

....O

HH

.. ..N

F....

..

..

Cl.. ....H

H F.. ....