The Foundations of Chemistry

EXAMPLE 18-5 Calculations Involving pH and pOH

Calculate [H 3 O
], pH, [OH], and pOH for a 0.015 MHNO 3 solution.

Plan

We write the equation for the ionization of the strong acid HNO 3 , which gives us [H 3 O
].
Then we calculate pH. We use the relationships [H 3 O
][OH]1.0 10 ^14 and
pH
pOH14.00 to find pOH and [OH].

Solution

HNO 3 
H 2 O88nH 3 O

NO 3 

Because nitric acid is a strong acid (it ionizes completely), we know that

[H 3 O
] 0.015 M

pHlog [H 3 O
]log (0.015)(1.82) 1.82

We also know that pH
pOH14.00. Therefore,

pOH14.00pH14.001.82 12.18

Because [H 3 O
][OH]1.0 10 ^14 , [OH] is easily calculated.

[OH]6.7 10 ^13 M

You should now work Exercise 27.

1.0 10 ^14



0.015

1.0 10 ^14



[H 3 O
]

All ions are hydrated in aqueous

solution. We often omit the

designations (
), (g), (s), (aq), and

so on.

18-3 The pH and pOH Scales 759

TABLE 18-3 Relationships Among[H 3 O
], pH, pOH,and [OH]

[H 3 O
] pH pOH [OH]

10 ^1515  1101

10 ^141401

10 ^1313110 ^1

10 ^1212210 ^2

10 ^1111310 ^3

10 ^1010410 ^4

10 ^99510 ^5

10 ^88610 ^6

10 ^77710 ^7

10 ^66810 ^8

10 ^55910 ^9

10 ^441010 ^10

10 ^331110 ^11

10 ^221210 ^12

10 ^111310 ^13

1 0 14 10 ^14

101  11510 ^15

H

O 3

 concentration

OH



concentration

Neutral

Increasing acidity

Increasing basicity