# PH: product of concentration of H+ and OH-

1. Sep 30, 2005

### amcavoy

Why is the following true?:

$$\left[H^+\right]\left[OH^-\right]=10^{-14}$$

It seems like they would cancel out (equal 10-7 instead). Thanks for your help.

2. Sep 30, 2005

### Zeth

What substance are you talking about? pH depends on many factors and you give none. How ever if you are talking about water at standard conditions then it does indeed cancel out to 10^-7.

3. Sep 30, 2005

### Tom Mattson

Staff Emeritus
It does not equal $10^{-7}$.

The $pH$ of water is 7, and so is the $pOH$.

$pH+pOH=7+7=14$

$-log[H^+]-log[OH^-]=14$

$-log([H^+][OH^-])=14$

$log([H^+][OH^-])=-14$

Exponentiating both sides in base 10 gives you the result in the opening post. That result holds true no matter how acidic or how basic your solution gets.

Last edited: Sep 30, 2005
4. Sep 30, 2005

### amcavoy

Ok thanks. I didn't realize it was for water when I looked at it.