WHAT IS pH ?

pH, pronounced "P - H", is the unit of measure used to express the degree of acidity of a substance.   pH is an abbreviation for "parts Hydrogen".

The pH scale goes from 0 (very acidic) to 14 (very alkali).

Lemon juice and vinegar are both acidic with pH values of 2 to 3.

Nitric acid and hydrochloric acid are very strong with pH of 0; stomach acid has a pH of 1.0

Addition of a strong acid, such as sulfuric acid ( H2SO4 ) to water makes the resulting solution very high in active acid concentration. This is called an acidic solution.

On the other end of the scale are the alkaline substances, which range from pH 8 to 14.

Common alkalis are seawater (pH 8), household ammonia (pH 11), oven cleaners (pH 13), and the very strong alkali, sodium hydroxide (pH 14).

The addition of a strong base or alkali material, such as sodium hydroxide ( NaOH ), to water makes the resulting solution very low in active acid concentration. This is called a very basic or alkali solution.

In between these two extremes is a pH of 7. This is the pH of pure water. Water, which is neither very acidic nor very alkali, is said to be neutral.

Technically, the scale actually refers to the concentration of positively-charged hydrogen (H+) ions and negatively-charged hydroxyl (OH-) ions in solution.

More hydrogen ions than hydroxyl ions makes an acidic solution, while an alkaline solution contains more hydroxyl ions than hydrogen ions.

The pH scale is a logarithmic one, meaning that each pH unit has 10 times as many hydrogen ions as the unit above it.

So, at pH 4, there are 10 times more hydrogen ions than at pH 5 and 100 times more hydrogen ions than at pH 6.

The following table will give you an idea of the pH values of common substances:

Substance                     pH Value

Stomach acid              1.0

Lemon Juice                2.4

Vinegar                          2.8

Orange Juice                3.0

Tomato Juice               4.0

Black Coffee                5.0

Detergent                      6.5

Milk                                 6.8

Blood                             7.4        (Saliva and Spinal Fluid should also be 7.4 pH;

                                                       Vaginal ph is acidic - about 4)

Seawater                       8.0

Baking soda                 9.0

Milk of Magnesia         10.7

Domestic Bleach        11.0

Caustic Soda               14.0

(Adapted from General Chemistry by Brady and Humiston, 1986)

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