Acids and Bases

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Slide 1

Acids and Bases

Chapter 14

Arrhenius Concept: Acids produce H+ in solution, bases produce OH ion.

Brønsted-Lowry: Acids are H+ donors, bases are proton acceptors.

HCl + H2O  Cl + H3O+

acid base conjugate conjugate

base acid

Proton is transferred from the HCl molecule to the water molecule.

Slide 2

Figure 14.1 The Reaction of HCI and H2O

Figure 14.2 The Reaction of an Acid with Water

Figure 14.3 The Reaction of NH3 with HCI to Form NH4+ and CI-

Slide 3

Conjugate Acid/Base Pairs

HA(aq) + H2O(l)  H3O+(aq) + A(aq)

conj conj conj conj

acid 1 base 2 acid 2 base 1

Conjugate base: everything that remains of the acid molecule after a proton is lost.

Conjugate acid: formed when the proton is transferred to the base.

A conjugate acid-base pair consists of two substances related to each other by the donating and accepting of a single proton.

Slide 4

Acid Dissociation Constant (Ka)

HA(aq) + H2O(l)  H3O+(aq) + A(aq)

Where, Ka is the acid dissociation constant. In dilute solution we can assume that the concentration of liquid water remains essentially constant when an acid is dissolved.

Slide 5

Acid Strength

The strength of an acid is defined by the equilibrium position of its dissociation

(ionization) reaction:

HA(aq) + H2O(l) H3O+(aq) + A-(aq)

Strong Acid:

Its equilibrium position lies far to the right. (HNO3)

Yields a weak conjugate base. (NO3)

Common strong acids are H2SO4, HCl, HNO3, HClO4

Slide 6

Figure 14.4 Graphic Representation of the Behavior of Acids of Different Strengths in Aqueous Solution

Slide 7

Figure 14.5 Acid Strength Versus Conjugate Base Strength

Slide 8

Acid Strength (continued)

Weak Acid:

Its equilibrium lies far to the left. (CH3COOH)

Yields a much stronger (it is relatively strong) conjugate base than water. (CH3COO)

Common weak acids are H3PO4, HNO2, HOCl, organic acids (-COOH).

Slide 9

Figure 14.6 A Strong Acid (a) and a Weak Acid (b) in Water