1

ACID- BASEEQUILIBRIA

H O l2 ( )

NO aq H O aq31

31 ( ) ( )

ACID- BASEEQUILIBRIAACID- BASEEQUILIBRIAACID- BASEEQUILIBRIA

LEWIS ACIDS & BASESACID = ELECTRON PAIR ACCEPTORBASE = ELECTRON PAIR DONOR

MUST HAVE AN UNSHARED PAIR OF ELECTRONS TO DONATE TO THE COVALENT BOND BETWEEN THE ACID AND BASE

H+ + NH3 NH41+

H+ +

H

N H

H

:

H

H N H

H

+

Al3+ + 6 H2O Al(H2O)6

H2O + SO3 H2SO4

BF3 + NH3 BF3 - NH3

BRONSTED - LOWRYBRONSTED ACIDS AND BASES

SPECIAL CASE OF THE LEWIS ACID-BASE THEORYACID IS A PROTON DONOR H+

BASE IS A PROTON ACCEPTOR

MUST HAVE UNSHARED PAIR OF ELECTRONS

O + NH3

ooC

H3C

O

O Ho o

o oC

H3C

O

o o

o ooo- + NH4

1

THAT IS, MUST BE A LEWIS BASE

ACID - BASE REACTION NEUTRALIZATION

PROTON BOUND TO A VERY ELECTRONEGATIVE ATOM

NOT AN ACID PROTON

ACID:

ARRHENIUS: PRODUCES H1+ IN WATER

BASE:

ARRHENIUS: PRODUCES OH1- IN WATER

BRONSTED: PROTON DONOR

BRONSTED: PROTON ACCEPTOR

LEWIS: HAS EMPTY ORBITAL

LEWIS: HAS e- PAIR AVAILABLE TO SHARE

+

SALT + WATERNEUTRALIZATION

DIFFERENCE: BRONSTED ACID HAS A PROTON!

NAMING ACIDS

BINARY:

UNLESS DISSOLVED IN WATER -- COVALENT

HBr

HYDROGENHYDRO BROMIDEBROMICHYDROBROMIC ACID

HFHI

HYDROFLUORIC ACIDHYDROIODIC ACID

POLYATOMICANIONS

-ITE = OUS OR -ATE = ICEXCEPTING S OR P

CO3 2- CARBONATE IONH2 CO3 IC ACID

SO42- = SULFATE ION H2 SO4 = SULFURIC ACID

SO32- = SULFITE ION H2 SO3 = SULFUROUS ACID

ACID BASE

BASE ACID

CONJUGATE

CONJUGATE

BRONSTED ACID-BASE CONJUGATE PAIRS

HCOOH (aq) + H2 O (l) HCOO1- (aq) + H3 O1+ (aq)

HOBr (aq) + H2 O (l) OBr1- (aq) + H3 O1+ (aq)

CONJUGATECONJUGATE

CONJUGATECONJUGATE

CONJUGATE PAIRS DIFFER BY A SINGLE PROTON!!!

O + NH3o

oC

H3C

O

O Ho o

o oC

H3C

O

o o

o ooo

- + NH41

CH3COOH (aq) + NH3 (aq) CH3COO1- (aq) + (aq)NH41

]NH][COOHCH[

]NH][COOCH[K

33

14

13

a

IF K >> 1, DISSOCIATION IS EXTENSIVEREACTION IS EXTENSIVE

IF K << 1, DISSOCIATION IS NOT EXTENSIVE

THE LARGER THE VALUE OF K, THE MORE EXTENSIVEIS THE REACTION

H2S (aq) + H2O (l) HS1- (aq) + H3O1+ (aq)

K = [HS1-] [H3O1+]

[ H2S]a

Kb = 1 X 10-14 / KaTHE LARGER THE VALUE OF K, THE STRONGER IS THE

ACID OR THE BASE

FOR ACID: THE MORE H3O1+ ION IS PRODUCED

FROM ACID - BASE CHART:

HIGH Ka + HIGH Kb = EXTENSIVE REACTION

RESULT: K>1 IF PRODUCT IS THE WEAKER ACID OR BASE OF THE CONJUGATE PAIR

ACID-BASE STRENGTH

BINARYHA

STRENGTH OF THE HA BOND

ELECTRONEGATIVITY OF A

OXOACID(OXYANION)

X-O- H

OXIDATION STATE OF XELECTRONEGATIVITY OF X

USUALLY: STRONGER BOND = WEAKER ACID

RESULT: K>1 IF PRODUCT IS THE WEAKER ACID OR BASE OF THE CONJUGATE PAIR

]OH[

]OH[K

13

13

a

H2O (l) + H301+ H2O (l) + H301+

WEAK ACID:Ka < Ka FOR H3O1+ Ka << 1

STRONG ACIDS:HX WHERE X = Cl, Br, IHNO3, HClO4, H2SO4

WEAK BASE:Kb < Ka FOR H3O1+ Kb << 1

STRONG BASE: SOLUBLE METAL HYDROXIDE

H2O (l) + H2O (l) H3O1+ (aq) + OH1- (aq)

K = Kw = [H3O1+][OH1-] = 1.0 x 10-14 AT 25 oC

[H3O1+] > [OH1-] ACIDIC SOLUTION

[H301+] = [OH1-] NEUTRAL SOLUTION

[H3O1+] < [OH1-] BASIC SOLUTION

[H3O1+] = [OH1-] = 1.0x10-7 M

pH = -log [H3O1+]

<7

= 7

>7

pK = -logKa

-log[1.0x10-7 ]

pKa + pKb = 14pH + pOH = 14 Ka x Kb = 1.0 x 10-14

0 2 4 6 7 8 10 12 14

14 12 10 8 7 6 4 2 0

pOH

pH

Scales to determine Acidity or Alkalinity

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

NEUTRAL

ACIDIC

BASIC

GASTRIC JUICE, 0.1 M HClORANGE JUICE

COKE, VINEGAR

WINETOMATO, BEERBLACK COFFEE

RAINSALIVA URINEHUMAN MILKBLOOD, TEARS

SEAWATER, EGG WHITEBILEBAKING SODA

BORAX

NAIR

HOUSEHOLD AMMONIADRAIN CLEANER,

0.1 M NaOH

14

WHAT IS THE pH of:

A. SOLUTION WHERE [H3O1+] = 3.6x10-6 MB. 0.25 M HClC. SOLUTION WHERE [OH1-] = 2.5x10-3 M

WHAT IS THE [OH1-] CONC. OF A pH = 4.5 SOLUTION?

pH = -log[H3O1+] Kw = [H3O1+][OH1-]= 1.0 x 10-14

A. pH = - LOG[3.6x10-6] = 5.4 (AN ACIDIC SOLUTION)

B. pH = -LOG[0.25] = 0.60

C. [H3O1+] [2.5x10-3] = 1.0x10-14= 4.0x10-12

pH = -LOG[4.0x10-12] = 11.4 (A BASIC SOLUTION)

[3.2x10-5][OH1-] = 1.0 x 10-14

[H3O1+] = 10-pH = 10-4.5 = 3.2x10-5

= 3.1x10-10 M

[H+] pH [OH-] pOHAcid, Base or Neutral

10-9

10-4

8

9

10-7

6

5

Titration Sample problem

• What volume of 1.0 M HCl is needed to neutralize 30.0 mL of 2.5 M NaOH?

Try These:

• What is the molarity of 5.0 mL of acid used to neutralize 10.0 mL of 2.5 M base?

• What volume of 1.0 M base is needed to neutralize 20.0 mL of 2.3 M acid?