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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: curiousgeorge1234 on February 09, 2007, 02:00:36 PM

Title: calculating concentration from pH
Post by: curiousgeorge1234 on February 09, 2007, 02:00:36 PM

I know how to calculate pH: -log [H+] for example.

But, if you are given the pH, ie. pH -1.00, how do you calculate the concentration?

Title: Re: calculating concentration from pH
Post by: Dan on February 09, 2007, 02:43:48 PM

Law of logs. log(x) usually (and in this case) is log₁₀(x)

if log(x) = y

x = 10^y

Title: Re: calculating concentration from pH
Post by: curiousgeorge1234 on February 09, 2007, 03:04:46 PM

so, if the pH is -1.00

x= 10^ -1

is that correct?

Title: Re: calculating concentration from pH
Post by: Dan on February 09, 2007, 03:05:36 PM

Careful, pH = -log[H] remember

Title: Re: calculating concentration from pH
Post by: curiousgeorge1234 on February 09, 2007, 03:07:06 PM

then, x = 10^1

Title: Re: calculating concentration from pH
Post by: Dan on February 09, 2007, 03:08:11 PM

yes

Title: Re: calculating concentration from pH
Post by: yolop on February 14, 2007, 04:37:28 PM

Last time I checked the pH scale was 0-14.  -1 should be wrong unless you just made it up. 

to calculate pH from a [H] or [OH-] you take the antilog.

Title: Re: calculating concentration from pH
Post by: enahs on February 14, 2007, 09:38:52 PM

A negative number for a pH is perfect legit.

And you are right about the antilog. But what happens if you take the antilog of 1? You get 0. If you take the antilog of 2, you get a negative number. Are you saying it is impossible to have 2 Molar concentration of an acid?