Chemistry by Mortimer Charles E

Author:Mortimer, Charles E
Language: eng
Format: epub
Tags: Chemistry
Publisher: Belmont, Calif. : Wadsworth Pub. Co.
Published: 1983-01-05T16:00:00+00:00

Example 15.8

What is the pH of a solution for which [OH~] = 0.030 M?

Solution

[OH-] = 3.0 X 10~^

log[OH-] = log 3.0 + log 10"-

= 0.48 - 2.00 = -1.52

pOH = 1.52

;;H = 14.00 - pOU

= 14.00 - 1.52 = 12.48

An alternative solution is

[H + ][OH~] = 1.0 X 10"'*

10 X 10" 3.0 X 10"^

log[H + ] = log3.3 + log 10"'^

= 0.52 - 13.00 = -12.48

pH = 12.48

Example 15.9

What is the [H + ] of a solution with a pH of 10.60?

Solution

Since

;7H-log[H^]

log[H + ] = -pH

In the present example, pH — — 10.60, and therefore

log[H^] = -10.60

[H + ] = 10-'°^° = 2.5 X 10"'' M

If a logarithm table is used, the value of log [H"^] must be divided into two parts: a decimal portion (which is called a mantissa and which must be positive) and a negative whole number (which is called a characteristic). Thus,

log[H + ] = -10.60 - 0.40 - 11.00 [H""] = antilog0.40 x antilog(-ll)

382

Chapter 15 Ionic Equilibrium, Part I

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