# pH

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 which are not acidic or alkaline (neutral) usually have a pH of 7. Acids have a pH less than 7. Alkalis have a pH 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 is able to tell 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 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:

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

[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 0 to 14, although extremely acidic or basic substances may have pH < 0, or pH > 14.

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

## Some common pH values

 pH 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

Neutralisation can be summed up by the formula:

H+ + OH- = H2O

(acid + alkali = water)