Acids-BasesArrhenius:

Acid…. A substance that increases the hydrogen ion, H+, concentration when dissolved in H2O. Eg. HCl, H2SO4, HC2H3O2 (CH3COOH), etc.

Base…. A substance that increases hydroxide ion, OH-, concentration.

Eg. NaOH, NH4OH, etc.

Bronsted-Lowry (1923) (not worried about increasing/decreasing H+ or OH- concentrations)

Acid … a “proton donor”, p+ = H+, any formula HA.

Eg. HCl, H2SO4, HC2H3O2 (CH3COOH), etc.

Base …. A “proton acceptor” Eg. OH-, NH3 ; Cl-

Note: HOH can do both!

Really no different from Arrhenius.

This is different from Arrhenius!

Acid solutions:

HCl(g) + H2O(l) H3O+(aq) + Cl-

(aq)

H3O+(aq) = H+

(aq)

H :Cl:....

+

:O:..

..H

H ..

..H

H

:O:

H ++ :Cl:

..

..-

Hydrogen ion, H+, or hydronium ion, H3O+ has formed

HCl(g) + H2O(l) H+(aq) + Cl-

(aq)

Bronsted and Lowry would say the HCl donated a p+ (H+ion), and the water accepted a p+ (H+ion). Either way the HCl is an acid. The water is a base ….it was a proton acceptor!

Coordinate covalent bond

Arrhenius would say the concentration of H+ has increased.

Strength of an acid can be determined by conductivity.

12 M HCl

Good or poor electrolyte? Large or small # of ions?

good Large

HCl(g) + H2O(l) H3O+(aq) + Cl-

(aq) Initially: 100 0 0

@equil: 0 100 100

Ka = [H3O+] [Cl-]

[HCl]= Large value Strong Acid

Acids with Ka values greater then “1” are considered strong acids. They 100% ionize.

Note: 100% pure HCl is a poor conductor. Why? No ions!

Strength of an acid can be determined by conductivity.

Good or poor electrolyte? Large or small # of ions?Pure HC2H3O2 no conduction none

Diluted HC2H3O2 poor small

HC2H3O2 (g) + H2O(l) H3O+(aq) + C2H3O2

-(aq)

Initially: 100 0 0

@equil: 97 3 3

< 5% ionization….. Very weak acid

Weak acid

Ka = [H3O+][C2H3O2

-]

[HC2H3O2]= a Very small # = 1.76 X 10-5

Properties of Acids:

1. Conduct electricity if they ionize.

2. React with metals to form H2

3. Neutralize bases.

4. Turn litmus red

5. Taste sour

More Bronsted-Lowry Acid/Base info:General acid/base reaction:

HA + B = A- + HB+

acid1 base2 base1 acid2

conjugateAcid/base

pair

HCl(aq) + NH3(aq) = NH4+

(aq) + Cl-(aq)

acid1 base2 acid2 base1

Which direction is favored?

Which is a stronger acid? HCl…. Ka is larger

At equilibrium there is more ________________ product

Titration problems

What is the volume of a 0.325 M NaOH solution needed to just neutralize 65.2 ml of 1.37 M HNO3?Balanced equation:

1 NaOH + 1 HNO3 = 1 HOH + 1NaNO3

65.2ml x x x x x

= 274.8 = 275ml NaOH

Or using: MaVa#H’s = MbVb

#OH’s(1.37M)(65.2ml)(1) = (0.325M)(Vb)(1)

Vb = 275ml

* Since they equal the same # of moles!

Basic Solutions:Strong Arrhenius bases:

1. Group IA hydroxides. Eg. NaOH, KOH

2. Lower Group IIA hydroxides. Eg. Sr(OH)2, Ba(OH)2

100% “Dissociate”: NaOH(S) Na+(aq) + OH-

(aq)

1.0 M Ba(OH)2 = 1.0mol Ba+2 + 2.0mol OH-

The Kb for these bases would be very large; > than 1.

They would also be good conductors of electricity.

1. Acid anions of weak acids: eg. C2H3O2-, from HC2H3O2

or OH-, from HOH

Strong Bronsted-Lowry bases:

More Bronsted-Lowry Acid/Base info:

Bases react with water to produce OH-

General equation: B(g) + H2O(l) = BH+(aq) + OH-

(aq)

NH3(g) + H2O(l) NH4+

(aq) + OH-(aq)

Base1 acid2 acid1 base2

Kb =

[NH4+][OH-]

[NH3]= 1.79 x 10-5

Which direction is favored in the reaction?

Lewis Acid/Base

Lewis acid: electron pair acceptor

Lewis base: electron pair donor

H+ + :N:....

H

HH

Lewisacid

Lewisbase

..

..H

H

H

H : :N

+

“adduct” … the product of a L.acid/base rxn

Acid-Base EquilibriaReview:

In pure water & all aqueous solutions:

H2O + H2O = H3O+ + OH-

Kw = [H3O+][OH-] = 1 x 10-14

[H3O+] = [OH-] = 1x10-7or =

[H3O+] > [OH-] = Acidic solution

[H3O+] < [OH-] = Basic solution

[H3O+] = [OH-] = Neutral solution

Solutions of Strong Acids/ Bases:0.10 M HNO3 actually consists of 0.10 M H3O+ or [H+] = 0.10 M

0.10 M NaOH…. Adds 0.10 OH- to the water solutionIonization & dissociation are 100% for strong acids & bases

HNO3 + H2O = H3O+ + NO3-

NaOH + H2O = Na+ (aq) + OH-

(aq)

In 0.10M Ba(OH-)2 [OH-] =

GONEGONE

In 0.20 M H2SO4 [H+] =

0.20M

0.40 M

pHA simple scale for ranking the H3O+ concentrations of dilute acid/base solutions. (Sorenson).

pH = - Log [H3O+ ]

The logarithm of a number is that number expressed as an exponent of the base 10.

For example, the logarithm of 1 is 0, 1 x 100.

If [H3O+] = 0.001 =

pH = -log 0.001 =If this is 1

This is the pH1x10-3

3

pH Scale

neutral

pH 7

[H3O+] 1x10-7

[OH-] 1x10-7

pOH 7

Acidity increases

10-6

6

10-8

8

0 1 2 3 4 5

100 10-1 10-2 10-310-410-5

10-12

12

[H3O+][OH-]= 1x10-14

pH = - log[H3O]

pH + pOH = 14

Formulas to remember

1M HA

8

10-8

10-6

6

Basicity increases

9 10 11 12 13 14

10-9 10-10 10-11 10-12 10-13 10-14

10-3

3

1M BOH

100

[H3O+] = 3.25 x 10- 4

Given a 3.25 x 10-4 M HNO3 , solve for:

a. [H3O+]

b. pH =

c. [OH-] =

HNO3 is a strong acid. Thus, 3.25 x 10-4M HNO3 =

-log [3.25 x 10-4]

prediction

= -(-3.488) = 3.49

1 x 10-14

3.25 x 10-4= 3.08 x 10-11

d. pOH = -log [OH-] = -log [3.08 x 10-11] = 10.5

Or pOH = 14.00 –3.49 = 10.51

More About the pH Scale