Phenolphthalein ( 4,4'-dioxophthalophenone or 3,3-bis- (4-hydroxyphenyl) phthalide ) is a triphenylmethane dye, an acid-base indicator that changes color from colorless (at pH <8.2) to red- violet , βraspberry "(In alkaline); but in concentrated alkali it is again colorless . In concentrated sulfuric acid forms a pink cation .
| Phenolphthalein | |
|---|---|
 | |
 | |
| Are common | |
| Systematic name | 4,4'-dioxophthalophenone |
| Traditional names | Phenolphthalein, Purgen |
| Chem. formula | C 20 H 14 O 4 |
| Physical properties | |
| Molar mass | 318.31 g / mol |
| Density | 1.3 g / cmΒ³ |
| Thermal properties | |
| T. melt. | 261β263 Β° C |
| T. bale. | |
| Classification | |
| Reg. CAS number | 77-09-8 |
| PubChem | |
| Reg. EINECS number | |
| Smiles | |
| Inchi | |
| Chebi | |
| ChemSpider | |
| Phenolphthalein ( pH indicator ) | ||
| lower limit of pH 0 | upper limit of pH 8.2 | |
| orange | β | no |
| Phenolphthalein ( pH indicator ) | ||
| lower pH limit 8.2 | upper limit of pH 11 | |
| no ' | β | magenta |
| Phenolphthalein ( pH indicator ) | ||
| lower limit of pH 11 | upper limit of pH 12 | |
| magenta | β | no |
The substance is a colorless crystal , poorly soluble in water, but good in alcohol and diethyl ether.
Content
Synthesis
It is synthesized by condensation of phenol and phthalic anhydride at 105-110 Β° C in the presence of ZnCl 2 or concentrated sulfuric acid .
Chemical Properties
The fusion of phenolphthalein with NaOH produces 4,4'-dihydroxybenzophenone, when heated with conc. H 2 SO 4 - phenol and 2-hydroxyanthraquinone.
Application
As an indicator
Phenolphthalein changes color depending on the pH level of the medium [2] . It is able to exist in several forms, which turn one into the other with a change in acidity.
| The form | In | H 2 in | In 2β | In (OH) 3β |
|---|---|---|---|---|
| Structure | ||||
| pH | 0-3 | 4-7 | 8-10 | 12-14 |
| Medium reaction | highly acidic | slightly acidic and neutral | alkaline | strongly alkaline |
| Colour | Orange | Pink or fuchsin | Colorless | |
| Picture |
- β https://www.chemenu.com/products/CM157263
- β The table shows the approximate boundaries of the existence of structural modifications. The exact boundaries of the color transition are given in the info boxes on the right.
It is used in analytical chemistry for titration of aqueous solutions (use a solution in ethanol ).
Medical Use
Until certain carcinogenic properties were discovered, phenolphthalein was used in medicine as a laxative (purgen) for more than a century and a half, although it has cumulative properties and may be irritating to the kidneys.
Mnemonic Rules
To memorize the color of phenolphthalein in an alkaline medium (if used as an indicator), there are mnemonic rules:
Phenolphthalein - raspberry in alkalis
But despite this, it is colorless in acids.
Getting into acid for others is a failure,
But he will endure without sighs, without crying.
But in the alkalis of phenolphthalein
Not life will come, but solid raspberries!
Our phenolphthalein is brighter than the colors of all raspberries!
See also
- Litmus
- Methyl orange
Literature
- Bates R., Determination of pH. Theory and Practice, trans. from English, 2nd ed., L., 1972, p. 126.
- Chemical encyclopedia; in 5 t.; v.5 Three-Yatr; under the editorship of Zefirov N.S .; M .: Big Russian Encyclopedia, 1998.-783s; silt