How do you calculate the pH of a weak acid?
A handy expression to use is
This is a quick and useful method if you are given the
I'll derive it using the usual ICE method:
We assume that
Taking -ve logs of both sides
Here's an example:
If you can remember it then fine. If not you need to use the ICE method described in the answer by @Dr Hayek
By measuring the concentration of
Consider the dissociation of the following weak acid HA with initial concentration of
The expression of
that can be rounded to
Here is a video which summarizes this technique which requires use of the quadratic formula. The values are different than Dr. Hayek's example, but the technique is the same.
Video from: Noel Pauller