How to convert between pH and concentrations.


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Aim: How to convert between pH and concentrations.

Activity: Draw the pH scale.

Notes: Sörenson defined pH as the negative logarithm of the hydrogen ion concentration.

pH = – log [H+]

Remember that sometimes H3O+ is written, so

pH = – log [H3O+]

means the same thing.

So let’s try a simple problem: The [H+] in a solution is measured to be 0.010 M. What is the pH?

The solution is pretty straightforward. Plug the [H+] into the pH definition:

pH = – log 0.010

An alternate way to write this is:

pH = – log 10¯2

Since the log of 10¯2 is -2, we have:

pH = – (- 2)

Which, of course, is 2.