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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Gammagirl on March 23, 2018, 04:41:13 AM

Title: acid/ base formulas
Post by: Gammagirl on March 23, 2018, 04:41:13 AM

What are the criteria for using,
ph=7-1/2(pKb +log C)
ph=1/2(pKa + log c)

Title: Re: acid/ base formulas
Post by: Borek on March 23, 2018, 08:05:05 AM

The formula is based on approximations, so first step is to check whether they hold.

http://www.chembuddy.com/?left=pH-calculation&right=pH-weak-acid-base

Title: Re: acid/ base formulas
Post by: Borek on March 23, 2018, 07:30:42 PM

Derivation of the [itex][H^+] = \sqrt{K_aC_a}[/itex] formula requires some simplifying assumptions - if they are not meet, you can't use the formula.

Whether it is better to calculate [H⁺] of [OH^-] depends on the data you have, as long as the assumptions are meet you can use the formula that better fits the data you have, they are in many ways equivalent.

Title: Re: acid/ base formulas
Post by: Borek on March 24, 2018, 08:01:29 AM

They are described on the page I linked to, have you tried to read it?