Acids and Bases. Arrhenius Acids and Bases

Page
2

HNO3 Ca(OH)2

H2SO4 Ba(OH)2

HClO4 Sr(OH)2

HNO3 → H+ + NO3-

Slide 11

2. Weak Acids and Bases

Partially dissociate or ionize, reaching some dynamic equilibrium state.

Rxn normally shown with double headed arrow.

HCN ⇌ H+ + CN-

Weak acids and bases significant in biological systems.

Slide 12

F. Examples of Organic Weak Acids and Bases

Carboxylic Acids: (weak acids)

RCO2H or RCOOH

Anion formed by ionization is resonance stabilized

Examples: pyruvic acid, lactic acid, acetic acid

Amines: (weak bases)

Based on ammonia, with differing # of “R” groups

Primary, secondary, tertiary

Slide 13

G. Polyprotic Acids and Bases

Polyprotic acids can donate more than one proton sequentially.

H2SO4

H3PO4

H2S

Polyprotic bases can accept more than one proton sequentially.

SO42-

PO43-

S2-

Slide 14

Self-Ionization of Water

Description

Pure water slightly ionizes on its own (autoionizes)

with equilibrium reactant favored.

H2O(l) + H2O(l) ⇌ H3O+(aq) + OH-(aq)

Determine the Kc value.

Slide 15

Kc for water ionization = Kw

Kw = ionization constant for water or

= ion product constant for water

Kw = [H+] [OH-] = 1 x 10-14 at 25oC

What are [H+] and [OH-] for pure water at 25oC?

Slide 16

True for Water and Dilute Aqueous Solutions

(Including Acid and Base Solutions of Interest)

[H+] [OH-] = 1 x 10-14 or

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

Neutral Solution [H+] = [OH-]

Acidic Solution [H+] > [OH-]

Basic Solution [H+] < [OH-]

or [H3O+]

Slide 17

pH Scale

In most aqueous weak acid and base solutions, the H+ concentrations are very small. Easier to express concentrations using a logarithic relationship. p = - log

Thus: pH = -log [H+]

pOH = -log [OH-]

Slide 18

What is the relationship between pH and pOH?

[H+] [OH-] = 1 x 10-14

(-log [H+]) + (-log [OH-]) = -log (1 x 10-14)

pH + pOH = 14

pH + pOH = 14

Slide 19

The pH Scale

Since pH is a logarithic scale, cola drinks (pH about 2.5) are about times as acidic as tomatoes (pH about 4.5)