Acid Dissociation

Kelter, Carr, Scott, Chemistry A World of Choices 1999, page 280

HCl

Conjugate baseAcid

Conjugate pair

+

1-

Cl

H

Conjugate Acid-Base Pairs

HCl + H2O H3O+ + Cl-acid base

base acid

conjugates

conjugates

HCl + H2O H3O+ + Cl-acid base CA CB

Conjugate Acid-Base Pairs

NH3 + H2O NH41+ + OH-

base acid

acid base

conjugates

conjugates

base acid CA CB

NH3 + H2O NH41+ + OH-

Water is Amphoteric

base acid CA CB

NH3 + H2O NH41+ + OH-

HCl + H2O H3O+ + Cl-acid base CA CB

Amphoteric or Amphiprotic substancesAmphoteric or Amphiprotic substances:Substances which can act as either proton donors (acids) or proton acceptors (bases) depending on what substances are present.

Amphoteric1-

+ +

sulfuric acidH2SO4

waterH2O

hydrogen sulfateion

HSO4-

hydronium ion

A substance that can act as either an acid or a base.

H3O+

1+

1-

+ +

sulfate ionSO4

2-

water

H2O

hydrogen sulfateion

HSO4-

hydroxide ionOH-

1-

2-

1-

+ +1+

sulfuric acid

H2SO4

water

H2O

hydrogen sulfateion

HSO4-

hydronium ion

H3O+

(HSO4- as a base)

Amphoteric

A substance that can act as either an acid or a base.

Amphoteric

A substance that can act as either an acid or a base.

1-

+

hydrogen sulfateion

HSO4-

hydroxide ion

OH-

1-+

sulfate ion

SO42-

water

H2O

2-

(HSO4- as an acid)

Conjugate Acid-Base Pairs

HC2H3O2 + H2O H3O1+ + C2H3O2OH-

acid1 base1

base2 acid2

conjugates

conjugates

acid base CA CBHC2H3O2 + H2O H3O1+ + C2H3O2OH-

The reaction proceeds in the direction such that the stronger acid donates its proton to the stronger base.