pH

pH is a measure of the concentration of hydrogens ions (= H+) (= protons) in a solution.

Numerically it is the negative logarithm of that concentration expressed in moles per liter (M).

Pure water spontaneously dissociates into ions, forming a 10-7 M solution of H+ (and OH-). The negative of this logarithm is 7, so the pH of pure water is 7.

Solutions with a higher concentration of H+ than occurs in pure water have pH values below 7 and are acidic.

Solutions containing molecules or ions that reduce the concentration of H+ below that of pure water have pH values above 7 and are basic or alkaline.

Is pH important? Yes!

The properties of most proteins, enzymes for example, are sensitive to pH.

As the pH drops,

The result: Not only does the net charge on the molecule change (it becomes more positive) but many of the opportunities that its R groups have for ionic (electrostatic) interactions with other molecules and ions are altered.

As the pH rises,

The result: Again the net charge on the molecule changes (it becomes more negative) and, again, many of the opportunities its R groups have for electrostatic interactions with other molecules or ions are altered.

Link to an example of the importance of pH in separating serum proteins by electrophoresis.

The pH of the cytosol within a human cell is about 7.4. BUT, this value masks the pH differences that are found in various compartments within the cell. For example,
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14 June 1999