PH

Water molecules are constantly splitting apart ("dissociating") into a hydrogen ion (H+) and a hydroxyl (OH-) ion, and just as rapidly, these ions recombine to form water. Acidity is produced by hydrogen ions and alkalinity is produced by hydroxyl ions. In pure water, the concentration of hydrogen ions and hydroxyl ions is equal, and the solution is neutral - neither acidic nor alkaline.

• In pure water, the equilibrium concentration of H+ and OH- is 0.0000001 (10-7) gram moles per liter. Gram moles per liter of H+ is written [H+].

• Some dissolved substances affect the relative concentration of H+ and OH-, making the solution acidic or basic.

• Since H+ and OH- will recombine whenever possible, when H+ goes up, OH- must go down, and vice versa.

• H+ and OH- concentrations can vary through a huge range, from 1 gm mole/liter to 0.00000000000001 (10-14) gm mole/liter.

• To deal with ranges of numbers this large, scientists usually use logarithms, or powers of 10. In typical laboratory solutions, [H+] may vary from about 0.01 gm mole/liter (10-2) to 0.0000000000001 gm mole/liter (10-13).

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