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pH (potential of hydrogen) is a scale of acidity from 0 to 14. It tells how acidic or alkaline a substance is. More acidic solutions, have lower pH. More alkaline solutions, have higher pH. Substances that aren't acidic or alkaline (neutral) usually have a pH of 7. Acids have a pH that is less than 7. Alkalis have a pH that is greater than 7.

There are a lot of ways for finding the pH of something. One way is to use litmus paper. The pH paper can tell you how strong the chemical is, whether it is a stronger acid or a stronger base.

pH is a measure of the concentration of protons (H+) in a solution. S.P.L. Sørensen introduced this concept in the year 1909. The p stands for the German potenz, meaning power or concentration, and the H for the hydrogen ion (H+).

The formula for calculating pH is:

[math]\mbox{pH} = -\log_{10} \left[ \mbox{H}^+ \right][/math]

[H+] indicates the concentration of H+ ions (also written [H3O+], the equal concentration of hydronium ions), measured in moles per litre (also known as molarity).

Most substances have a pH in the range of 0 to 14, although extremely acidic or alkaline substances may have pH < 0, or pH > 14.

Alkaline substances have, instead of Hydrogen ions, a concentration of Hydroxide ions (OH-).

Some common pH values

Battery acid 1.0
Gastric acid 2.0
Lemon juice 2.4
Cola 2.5
Vinegar 2.9
Orange or apple juice 3.5
Beer 4.5
Acid rain < 5.6
Coffee 5.0
Tea 5.5
Milk 6.5
Pure water 7.0
Healthy human saliva 5 - 8
Blood 7.35 - 7.45
Sea water 8.0
Hand soap 9.0 - 10.0
Household ammonia 11.5
Bleach 12.5
Household lye 13.5
Caustic soda 12.7


Neutralisation can be summed up by the formula:

H+ + OH- = H2O

(acid + base = water)

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