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Phenolphthalein

Phenolphthalein
Phenolphthalein-low-pH-2D-skeletal.svg
Sample of solid phenolphthalein.jpg
Names
Preferred IUPAC name
3,3-Bis(4-hydroxyphenyl)-2-benzofuran-1(3H)-one
Other names
3,3-Bis(4-hydroxyphenyl)isobenzofuran-1(3H)-one
Identifiers
77-09-8 YesY
3D model (Jmol) Interactive image
ChEMBL ChEMBL63857 YesY
ChemSpider 4600 YesY
DrugBank DB04824 N
ECHA InfoCard 100.000.914
KEGG D05456 YesY
PubChem 4764
UNII 6QK969R2IF N
Properties
C20H14O4
Molar mass 318.328 g·mol−1
Appearance White powder
Density 1.277 g/cm3 (32 °C (90 °F))
Melting point 258–263 °C (496–505 °F; 531–536 K)
400 mg/L in water
Solubility in other solvents Insoluble in benzene or hexane, very soluble in ethanol and ether, slightly soluble in DMSO
UV-vis (λmax) 552 nm (1st)
374 nm (2nd)
Pharmacology
A06AB04 (WHO)
Hazards
GHS pictograms The health hazard pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word Danger
H341, H350, H361
P201, P281, P308+313
Toxic T Harmful Xn
R-phrases R22, R40, R45, R62, R68
S-phrases S53, S45
NFPA 704
Flammability code 3: Liquids and solids that can be ignited under almost all ambient temperature conditions. Flash point between 23 and 38 °C (73 and 100 °F). E.g., gasoline) Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
N  (what is YesYN ?)
Infobox references

Phenolphthalein is a chemical compound with the formula C20H14O4 and is often written as "HIn" or "phph" in shorthand notation. Phenolphthalein is often used as an indicator in acid–base titrations. For this application, it turns colorless in acidic solutions and pink in basic solutions.

Phenolphthalein is slightly soluble in water and usually is dissolved in alcohols for use in experiments. It is a weak acid, which can lose H+ ions in solution. The phenolphthalein molecule is colorless, and the phenolphthalein ion is pink. When a base is added to the phenolphthalein, the molecule ⇌ ions equilibrium shifts to the right, leading to more ionization as H+ ions are removed. This is predicted by Le Chatelier's principle.

Phenolphthalein's common use is as an indicator in acid-base titrations. It also serves as a component of universal indicator, together with methyl red, bromothymol blue, and thymol blue.

Phenolphthalein adopts four different states in aqueous solution: Under very strongly acidic conditions, it exists in protonated form, providing an orange coloration. Between strongly acidic and slightly basic conditions, the lactone form is colorless. The singly deprotonated phenolate form (the anion form of phenol) gives the familiar pink color. In strongly basic solutions, phenolphthalein's pink color undergoes a rather slow fading reaction and becomes completely colorless above 13.0 pH. The rather slow fading reaction that produces the colorless InOH3− ion is sometimes used in classes for the study of reaction kinetics.

Phenolphthalein's pH sensitivity is exploited in other applications: Concrete has naturally high pH due to the calcium hydroxide formed when Portland cement reacts with water. As the concrete reacts with carbon dioxide in the atmosphere, pH decreases to 8.5-9. When a 1% phenolphthalein solution is applied to normal concrete, it turns bright pink. However, if it remains colorless, it shows that the concrete has undergone carbonation. In a similar application, spackling used to repair holes in drywall contains phenolphthalein. When applied, the basic spackling material retains a pink coloration; when the spackling has cured by reaction with atmospheric carbon dioxide, the pink color fades.


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Wikipedia

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