Dr. S. M. Condren

Chapter 15

Acids and Bases

Dr. S. M. Condren

Arrhenius Acid-Base Theory

Arrhenius, Svante August• (1859-1927), Swedish chemist• 1903 Nobel Prize in chemistry

acid - proton donor

base - hydroxide ion donor

Dr. S. M. Condren

Bronsted-Lowry Acid-Base Theory

acid - proton donor

base - proton acceptor

strong vs. weak acids and bases• strong - completely ionized• weak - partially ionized

Dr. S. M. Condren

Acid-Base Reactions

hydronium ionhydrated proton, H3O+

used interchangeably for H+

indicatorsnatural or synthetic substance that changes

color in response to the nature of its chemical environment.

Dr. S. M. Condren

Indicators

• Indicators are used to provide information about the degree of acidity of a substance (pH) or the state of some chemical reaction within a solution being tested or analyzed.

Dr. S. M. Condren

Indicators

• One of the oldest indicators is litmus, a vegetable dye that turns red in acid solutions and blue in basic ones. Other indicators include alizarin, methyl red, and phenolphthalein, each one being useful for a particular range of acidity or a certain type of chemical reaction.

Dr. S. M. Condren

Indicators

Dr. S. M. Condren

Neutralization Reactions

acid + base ---> “salt” + water

HCl + NaOH ---> NaCl + H2O

Dr. S. M. Condren

Sulfur Acid

SO3 + H2O -----> H2SO4

Dr. S. M. Condren

Phosphoric Acid

P4O10(s) + 6H2O(l) ---> 4H3PO4(aq)

Dr. S. M. Condren

Strong vs. Weak Acids and Bases

strong acidcompletely ionized

weak acidpartially ionized

Dr. S. M. Condren

Which of the following "molecular" pictures best represents a concentrated solution of the weak acid HA with Ka = 10-5?

A, B

Dr. S. M. Condren

Autoionization of Water

H2O + H2O <=> H3O+ + OH-

[H3O+][OH-]K = -----------------

[H2O]2

Kw = K [H2O]2 = [H3O+][OH-] = 1.0 x 10-14

Dr. S. M. Condren

Autoionization of Water

Kw = K [H2O]2 = [H3O+][OH-] = 1.0 x 10-14

[H3O+][H3O+] = 1.0 x 10-14

[H3O+]2 = 1.0 x 10-14

[H3O+] = 1.0 x 10-7

-log([H3O+]) = -log(1.0 x 10-7)pH = -log([H3O+]) = 7.00

Dr. S. M. Condren

pH Scale

@ -2 -----> @ +16

pH = - log [H3O+]

Dr. S. M. Condren

A solution with pH=5 is 100 times more acidic than a solution with a pH =?

7, 3, 0.05

Dr. S. M. Condren

pH Scale