Working out pH?

Question

Okay, im doing chemistry homework. I cant work out how to get the pH if only the OH- is given. Can anyone give me a formula for doing it?

Daniel

Answer 1

pH + pOH =14... if you find the concentration of OH- in Molar you can take the -log of the concentration of OH-in Molar... and you subtract it from 14 and you will get the pH

Answer 2

The easy way to do this on your calculator is this:

Let say you have [OH-] = 3.25 Exp -9

Find its pOH by pressing "log"

You should get -8.4881 (so the pOH = +8.4881)

Don't change sign (+/-)

Just add 14 to the result, since pH + pOH = 14

You should get 5.5119

So pH = 5.5119

Easy .... right?

Answer 3

[OH-] = x

Kw = [H+][OH-] = 1 x10^-14

[H+]x = 1 x 10^-14

[H+] = (1x10^-14)/x

Log[H+] = Log {(1x10^-14)/x}

pH = -Log[H+] = -Log{(1x10^-14)/x}