Chemistry: about the pH scale

intothewild SG

Can anyone enlighten me something about the pH scale.

At 25 degree Celsius, the pH scale is from 0-14 ( right?)

So if I have a solution of HCl at 3moldm-3, the [H+] = 3moldm-3.

Now, since pH = -lg[H+], won't the pH of this HCl < 0, and it does not fit nicely into the pH scale, did I miss out a concept?

The pH scale does not apply to concentrated solutions??

Thanks a mil.

UltimaOnline SG

The pH scale has its limitations, in terms of usefulness. Insofar as the way the pH scale works, or is defined, or is calculated, then arguably, you can still use it for concentrated solutions, strong acids, and even super acids, and you will obtain a negative pH value, which is mathematically correct, no worries.

A more powerful scale for acidities would be the Hammett acidity function, that overcomes the limitations of the pH scale.

http://en.wikipedia.org/wiki/Hammett_acidity_function

This is for your additional information only. As far as the 'O' and 'A' levels are concerned, continue using the pH scale and its calculations, and don't worry when you (correctly) end up with negative pH values.