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PH Indicator

 
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A pH indicator is a halochromic
Halochromism

A halochromic material is a material which changes colour when pH changes occur. The term ?chromism? is defined as materials that can change colour reversibly with the presence of a factor....
 chemical compound
Chemical compound

A chemical compound is a Chemical substance consisting of two or more different chemical element Chemical bond together in a fixed mass ratio that can be split into simpler substances....
 that is added in small amounts to a solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
 so that the pH
PH

pH is a measure of the Acid or Base of a solution. It is defined as the cologarithm of the Activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations....
 (acid
Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
ity or alkalinity
Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
) of the solution can be determined easily. Hence a pH indicator is a chemical detector for hydronium
Hydronium

In chemistry, hydronium is the common name for the aqueous cation hydrogen3oxygen+ derived from protonation of water. It is the simplest type of an oxonium ion....
 ions (H3O+) (or Hydrogen ions (H+) in the Arrhenius model
Acid-base reaction theories

An acid-base reaction is a chemical reaction that occurs between an acid and a base . Several concepts exist which provide alternative definitions for the reaction mechanisms involved and their application in solving related problems....
). Normally, the indicator causes the color
Color

Color or colour is the visual perception property corresponding in humans to the categories called red, yellow, blue and others....
 of the solution to change depending on the pH. Solutions with a pH value above 7.0 are alkali, and solutions with a pH value below 7.0 are acidic.






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A pH indicator is a halochromic
Halochromism

A halochromic material is a material which changes colour when pH changes occur. The term ?chromism? is defined as materials that can change colour reversibly with the presence of a factor....
 chemical compound
Chemical compound

A chemical compound is a Chemical substance consisting of two or more different chemical element Chemical bond together in a fixed mass ratio that can be split into simpler substances....
 that is added in small amounts to a solution
Solution

In chemistry, a solution is a homogeneous mixture composed of two or more substances. In such a mixture, a solute is dissolved in another substance, known as a solvent....
 so that the pH
PH

pH is a measure of the Acid or Base of a solution. It is defined as the cologarithm of the Activity of dissolved hydrogen ions . Hydrogen ion activity coefficients cannot be measured experimentally, so they are based on theoretical calculations....
 (acid
Acid

An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion Activity greater than in pure water, i.e....
ity or alkalinity
Base (chemistry)

In chemistry, a base is most commonly thought of as an aqueous substance that can accept protons. A base is also often referred to as an alkali if OH- ions are involved....
) of the solution can be determined easily. Hence a pH indicator is a chemical detector for hydronium
Hydronium

In chemistry, hydronium is the common name for the aqueous cation hydrogen3oxygen+ derived from protonation of water. It is the simplest type of an oxonium ion....
 ions (H3O+) (or Hydrogen ions (H+) in the Arrhenius model
Acid-base reaction theories

An acid-base reaction is a chemical reaction that occurs between an acid and a base . Several concepts exist which provide alternative definitions for the reaction mechanisms involved and their application in solving related problems....
). Normally, the indicator causes the color
Color

Color or colour is the visual perception property corresponding in humans to the categories called red, yellow, blue and others....
 of the solution to change depending on the pH. Solutions with a pH value above 7.0 are alkali, and solutions with a pH value below 7.0 are acidic. Solutions with a pH value of 7.0 are neutral.

Theory

pH indicators themselves are frequently weak acids or bases. When introduced into a solution, they may bind to H+ (Hydrogen
Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the chemical symbol H. At standard temperature and pressure, hydrogen is a colorless, odorless, nonmetallic, tasteless, highly combustion and explosive Diatomic molecule gas with the molecular formula H2....
 ion) or OH- (hydroxide
Hydroxide

In chemistry, hydroxide is the name for the Diatomic molecule anion OH-, consisting of oxygen and hydrogen atoms, usually derived from the Dissociation of a base ....
) ions. The different electron configuration
Electron configuration

In atomic physics and quantum chemistry, electron configuration is the arrangement of electrons in an atom, molecule, or other physical structure....
s of the bound indicator causes the indicator's color to change, which allows the pH to be determined by the different colors.

Application

pH indicators are frequently employed in titration
Titration

Titration is a common laboratory method of quantitative Analytical chemistry that is used to determine the unknown concentration of a known reactant....
s in analytic chemistry
Chemistry

Chemistry is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions....
 and biology
Biology

Biology is a branch of the natural sciences concerned with the study of living organisms and their interaction with each other and their environment ....
 experiments to determine the extent of a chemical reaction
Chemical reaction

A chemical reaction is a process that always results in the interconversion of chemical substances. The substance or substances initially involved in a chemical reaction are called reactants....
. Because of the subjective
Subjectivity

Subjectivity refers to a subject's perspective or opinion, particularly feelings, beliefs, and desires. It is often used casually to refer to unjustified personal opinions, in contrast to knowledge and justified belief....
 determination of color, pH indicators are susceptible to imprecise readings. For applications requiring precise measurement of pH, a pH meter
PH meter

A pH meter is an electronic instrument used to measure the pH of a liquid . A typical pH meter consists of a special measuring probe connected to an electronic meter that measures and displays the pH reading....
 is frequently used.

Tabulated below are several common laboratory pH indicators. Indicators usually exhibit intermediate colors at pH values inside the listed transition range. For example, phenol red exhibits an orange color between pH 6.8 and pH 8.4. The transition range may shift slightly depending on the concentration of the indicator in the solution and on the temperature at which it is used.

Commercial preparations

Ph Indicator Paper
Universal indicator
Universal indicator

Universal indicator is a pH indicator that transitions through numbers 3-12 to indicate the acidity or alkalinity of solutions. Although there are a number of commercially available universal pH indicators, most are a variation of a formula patented by Yamada in 1923....
 and Hydrion paper
Hydrion paper

Hydrion is a trademarked name for a popular line of compound pH indicators, marketed by Micro Essential Laboratory, Inc. exhibiting a series of color changes over a range of pH values....
s are blends of different indicators that exhibits several smooth color changes over a wide range of pH values.

Naturally occurring pH indicators

Light Mauve Hydrangea
Many plants or plant parts contain chemicals from the naturally-colored anthocyanin
Anthocyanin

Anthocyanins are solubility vacuole pigments that may appear red, purple, or blue according to pH. They belong to a parent class of molecules called flavonoids synthesized via the phenylpropanoid pathway....
 family of compounds. They are red in acidic solutions and blue in basic. Extracting anthocyanins from red cabbage
Red Cabbage

The red cabbage is a sort of cabbage, also known as Red Kraut or Blue Kraut after preparation.Its leaves are coloured dark red/purple....
 leaves or the skin of a lemon
Lemon

The lemon is the common name for Citrus limon. The reproductive tissue surrounds the seed of the angiosperm lemon tree. The lemon is used for culinary and nonculinary purposes throughout the world....
 to form a crude acid-base indicator is a popular introductory chemistry demonstration.

Anthocyanins can be extracted from a multitude of colored plants or plant parts, including from leaves (red cabbage
Cabbage

The cabbage is a leafy garden plant of the Family Brassicaceae , used as a Leaf vegetable. It is a herbaceous, biennial plant, dicotyledonous flowering plant distinguished by a short stem upon which is crowded a mass of leaves, usually green but in some varieties red or purplish, forming a characteristic compact, globular cluster ....
); flowers (geranium
Pelargonium

Pelargonium is a genus of flowering plants which includes about 200 species of perennial plants, succulent plants, and shrubs, commonly known as geraniums or storksbills....
, poppy
Poppy

A poppy is any of a number of showy flowers, typically withone per Plant stem, belonging to the Papaveraceae. They include a number of attractive wildflower species with showy flowers found growing singularly or in large groups; many species are also grown in gardens....
, or rose
Rose

A rose is a perennial plant flower shrub or vine of the genus Rosa, within the family Rosaceae, that contains over 100 species and comes in a variety of colors....
 petals); berries (blueberries
Blueberry

Blueberries are flowering plants in the genus Vaccinium, sect. Cyanococcus. The species are native only to North America. They are shrubs varying in size from 10 cm tall to 4 m tall; the smaller species are known as "lowbush blueberries" , and the larger species as "highbush blueberries"....
, blackcurrant
Blackcurrant

The Blackcurrant is a species of Ribes berry native to central and northern Europe and northern Asia. It is also known as French "cassis".It is a small shrub growing to 1?2 m tall....
); and stems (rhubarb
Rhubarb

Rheum is a genus of perennial plants that grows from thick short rhizomes. The genus is in the family Polygonaceae, and includes the vegetable rhubarb The plants have large leaf that are somewhat triangular shaped with long fleshy Petiole s....
). An exhaustive list would be beyond the scope of this article.

See also

  • Bromothymol blue
    Bromothymol blue

    Bromothymol blue is a chemical pH indicator for weak acids and Base . The chemical is also used for observing Photosynthesis activities or respiratory indicators ....
  • Universal indicator
    Universal indicator

    Universal indicator is a pH indicator that transitions through numbers 3-12 to indicate the acidity or alkalinity of solutions. Although there are a number of commercially available universal pH indicators, most are a variation of a formula patented by Yamada in 1923....