pH/pOH

pH and pOH are a measure of how acidic or how basic a solution is and for most solutions, is measured on a scale of 0 to 14. The lower the number, the more acidic the solution is, and the higher the number, the more basic the solution is. Neutral solutions (not acidic or basic) have a pH of 7.

pH is measured on what we call a logarithmic scale, that means that for every number the pH changes, the concentration of H⁺ atoms changes by a factor of 10 (it becomes 10 times more acidic or basic)

The graph above shows how the logarithmic pH scale works.

The main things we need to know about pH and pOH are

14 = pH + pOH
pH = -log[H]
pOH = -log[OH]
Kw = 1x10^-14 = [H⁺] * [OH^-]

Example Question:

Complete the following table:

pH	[H⁺]	[OH^-]	pOH
			4
		1x10^-2

Answer:

pH = 14 - pOH

so your first pH = 10

to get [H⁺] from pH, take 10^-pH = 1x10^-10
to get [OH^-] from pOH, take 10^-pOH = 1x10^-4

2nd line

find pOH by taking -log(OH) = -log(0.01) = 2
pH = 14-2 = 12
[H⁺] = 10^-pH = 1x10^-12
So you end up with

pH [H⁺] [OH^-] pOH

10 1x10^-10 1x10^-4 4

12 1x10^-12 1x10^-2 2

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