Chemistry - A Molecular Science

d) What is the pH of a 0.022 M Ba(OH)

solution? 2

First, determine the hydroxide ion concentr

ation from the conc

entration of Ba(OH)

and 2

the fact that there are two moles of hydroxide ion in each mole of Ba(OH)

. 2

[OH

1-] =

0.022 mol Ba(OH)

2

L of solution

×

2 mol OH

1-

mol Ba(OH)

= 0.044 M 2

We use Equation 12.5 to obtain the hydronium ion concentration

[H

O 3

1+] =

1.0

×^10

-14

0.044

= 2.3

×^10

-13

M

and Equation 12.4 to determine the pH.

pH = -log [H

O 3

1+] = -log(2.3x10

-13

) = 12.64

Example 12.13

The pK

of phenol is 10.0 while the pKa

of the hydrogen sulfite (bisulfite) ion is 7.0. a

Which acid is the stronger acid? The strength of an acid increases as it pK

decreases, so the bisulfa

ite ion is the stronger

acid because it has the lower pK

. a

Chapter 12 Acid-Base Chemistry

Example 12.14

Indicate the solution with the greater hy

dronium ion concentration in each pair.

a) 0.10 M HNO

or 0.15 M HNO 2

? 2

The acids are identical, so the only differenc

e is concentration. The more concentrated

acid (0.15 M HNO

) has the greater hydronium ion concentration. 2

b) 0.10 M KF or 0.15 M KF?

Both are solutions of the same weak base, so the hydroxide ion concentration and pH increase with the concentration of the base.

Thus, the less concentrated base (0.10 M

KF) has the lower OH

1- concentration and the greater H

O 3

1+ concentration.

c) 0.05 M benzoic acid (pK

= 4.19) or 0.05 M lactic acid (pKa

= 3.85)? a

Lactic acid has the lower pK

, so it is the stronger acid and has the greater Ha

O 3

1+

concentration.

d) a solution with pH = 3 or one with a pH = 5?

The solution with the lower pH (pH = 3 solution) has the higher H

O 3

1+ ion concentration.

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Carolina

State

University