Chemistry - A Molecular Science

Chapter 12 Acid-Base Chemistry

Example 12.4 a) Write the conjugate base of each of the following acids:

H^2

O

Removal of one proton yields OH

1- (HOH

→

OH

1- + H

1+)

HCN

Removal of one proton yields CN

1- (HCN

→

CN

1- + H

1+)

H^2

PO

1- 4

Removal of one proton yields HPO

2- (H 4

PO 2

1- 4

→

HPO

2- 4

+ H

1+)

b) Write the conjugate acid of each of the following bases:

H

O 2

Addition of one proton yields H

O 3

1+^

(HOH + H

1+^

→

H^3

1+O

)

S

2-^

Addition of one proton yields HS

1- (S

2- + H

1+^

→

HS

1-)

H

PO 2

1- 4

Addition of one proton yields

H

PO 3

(H 4

PO 2

1- 4

+ H

1+^

→

H^3

PO

) 4

Note that H

O was used as an example of both an acid and a base in Example 12.4. 2

Substances that can function as either an acid or a base are said to be

amphiprotic

.

H^2

PO

1- 4

is another amphiprotic substance in Example 12.4.

Example 12.5 Example 12.5 Draw Lewis structures of the reactants and products of the following reactions. Draw Lewis structures of the reactants and products of the following reactions. Indicate the mechanism with curved arrows and include all nonzero formal charges. Indicate the mechanism with curved arrows and include all nonzero formal charges.

a) Hydrogen chloride gas is dissolved in water. a) Hydrogen chloride gas is dissolved in water.

Cl

H

OH

Cl

H

O

H

HH

+

HCl(g) + H

O(l) 2

→

Cl

1-

+ H

O 3

1+

The two conjugate acid-base pairs are (HCl, Cl

1-) and (H

O, H 2

O 3

1+).

b) Nitrous acid is added to a solution of ammonia.

O

N

O

N H

HH

H

O

N

O

N H

HH

H

+

HNO

(aq) + NH 2

(aq) 3

→

NO

1- + NH 2

1+ 4

The two conjugate acid-base pairs are (HNO

, NO 2

1- 2

) and (NH

, NH 3

1+ 4

).

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North

Carolina

State

University