- pH
-
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at 25 °C (77 °F). Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline. pH measurements are important in medicine, biology, chemistry, food science, environmental science, oceanography, civil engineering and many other applications.
Mathematical definition
pH is defined as a negative decimal logarithm of the hydrogen ion activity in a solution.
where aH is the activity of hydrogen ions in units of Mol/L (molar concentration).
Pure (neutral) water has a pH around 7 at 25 °C (77 °F); this value varies with temperature. When an acid is dissolved in water, the pH will be less than 7 (if at 25 °C (77 °F)). When a base, or alkali, is dissolved in water, the pH will be greater than 7 (if at 25 °C (77 °F)). A solution of a strong acid, such as hydrochloric acid, at concentration 1 mol dm−3 has a pH of 0. A solution of a strong alkali, such as sodium hydroxide, at concentration 1 mol dm−3, has a pH of 14. Thus, measured pH values will lie mostly in the range 0 to 14. Since pH is a logarithmic scale, a difference of one pH unit is equivalent to a tenfold difference in hydrogen ion concentration.
An approximate measure of pH may be obtained by using a pH indicator. A pH indicator is a substance that changes color around a particular pH value. It is a weak acid or weak base and the color change occurs around 1 pH unit either side of its acid dissociation constant, or pKa, value. For example, the naturally occurring indicator litmus is red in acidic solutions (pH<7 at 25 °C (77 °F)) and blue in alkaline (pH>7 at 25 °C (77 °F)) solutions. Universal indicator consists of a mixture of indicators such that there is a continuous color change from about pH 2 to pH 10. Universal indicator paper is simple paper that has been impregnated with universal indicator.
Prev: Biopolymer
Next: Reducing agent - 【Back】【Close 】【Print】【Add to favorite 】
-
Health and Chemical more >
-
Hot Products
- 15751-00-5 hexakis(1H-imidazole-N3)nickel(2+) dichloride
- 303-26-4 1-(4-Chlorobenzhydryl)piperazine
- 869942-54-1 N-(4-ethylbenzyl)butan-2-amine
- 844885-25-2 3,4-Dichloro-3'-methoxybenzophenone
- 1308-06-1 Tricobalt tetraoxide
- 5138-86-3 2-ETHYLBUTYL METHACRYLATE
- 35326-33-1 2-hydroxyprop-2-enoic acid
- 63-42-3 Lactose
- 80-23-9 Benzenesulfonamide,3-amino-4-hydroxy-N-methyl-
- 1308-38-9 Chromium oxide
- 618098-42-3 1-(2-Fluorophenyl)-3-(2-methylphenyl)-1H-pyrazol-5-amine
- 81406-93-1 Pliolite AC 80