What is pH
What is pH
Many compounds dissolve in water and alter the hydrogen ion concentration.
Compounds that produce hydrogen ions directly when dissolved in water are called acids, and those that produce hydroxyl ions directly when dissolved in water are called bases.
To treat these aspects of chemistry more precisely, a quantitative system of expressing acidity or basicity (alkalinity) is needed.
This need could be met by using the value of [H+], where [H+] is expressed in moles/liter, as a measure of acidity. But, in most cases [H+] is in the range of 10-1 to 10-14 moles/liter.
Because numbers of this magnitude are inconvenient to work with, an alternate system for expressing the acidity of dilute solutions has been devised.
This system is based on a quantity called pH. ph is defined as the negative logarithm of the hydrogen concentration, represented as [H+] in moles/liter.
pH = -log [H+]
[H+] = 10-pH
The negative logarithm is specified because the logarithm of any number less than 1 is negative; thus multiplication by -1 causes the values of pH to be positive over the range in which we are interested.
(The term pH was first defined by a Danish chemist and is derived from p for the Danish word potenz (power) and H for hydrogen.)
Example:
The hydrogen concentration, [H+], of a solution is 4.8 x 10-8 moles/liter.
What is the pH of the solution?
pH = -log [H+]
= -log (4.8 x 10-8)
= 7.32
this article is taken from: DOE FUNDAMENTALS HANDBOOK CHEMISTRY Volume 1 of 2 - DOE-HDBK-1015/1-93 JANUARY 1993
see also:
what is the effect of pH on corrosion
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