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.
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:
Most substances have a pH in the range 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[change | change source]
|Orange or apple juice||3.5|
|Acid rain||< 5.6|
|Healthy human saliva||5 - 8|
|Blood||7.35 - 7.45|
|Hand soap||9.0 - 10.0|
Neutralisation[change | change source]
Neutralisation can be summed up by the formula:
- H+ + OH- = H2O