# Why the PH scale has no unit?

###### Wiki User

###### 2010-03-27 20:41:53

pH has no unit because it's a it's a logarithmic scale, not a

measurement like grams or degrees.

The pH number directly relates mathematically to the actual

concentrations in solution. Concentration itself does have units,

but pH really only looks at the power (or exponent) of the

concentrations. And, for that reason the unit doesn't carry.

For example:

pH = - log [H30+] (mathematical definition)

= negative logarithm of the hydronium ion concentration.

What this means is that if a solution has a concentration of

10-7 M [H30+] or (0.0000001 moles per litre of the hydronium ion),

the negative log of this number = 7. Therefore the pH = 7.

But it's not 7 moles per litre or 7 moles or any other

transferable unit. It's just 7.

Hope that helps a little.