Phenolphthalein

Phenolphthalein /ˌfiː n  nɒ lf ˈθeɪ li  liː n  n/[1] is a chemical compound with compound with the for formul mula aC20H14O4 and is often written as "HIn "HIn"" or "phph "phph"" in shorthand notation. Often used in titrations titrations it turns colorless in acidic acidic solutions  solutions and pin! in asic asic solutions.  solutions. #f the concentration of indicator is particularl$ stron% it can appear purple. #n stron%l$ asic solutions phenolphthalein&s pin! color under%oes a rather slow fadin% reaction and ecomes colorless a%ain. 'he molecule has four forms(

H)#n*

H2#n

#n2+

#n,OH-)+

pH

0

0+.2

.2+12.0

12.0

Conditions

stron%l$ acidic

acidic or nearneutral

asic

stron%l$ asic

Color 

oran%e

colorless

pin! to fuchsia

colorless

Species

Structure

Model

Image

'he rather slow fadin% reaction that produces the colorless #nOH)+ ion is sometimes used in classes for the stud$ of reaction !inetics. henolphthalein is insolule in water  and  and usuall$ is dissol3ed in alcohols alcohols for  for use in eperiments eperiments.. #t is a wea! acid which can lose H* ions in solution. 'he phenolphthalein molecule is colorless howe3er the the phenolphthalein ion is pin!. 5hen a ase is added to the phenolphthalein the molecule ⇌ ions&

e6uilirium shifts to the ri%ht leadin% to more ioni7ation as H* ions are remo3ed. 'his is predicted $ 8e Chatelier&s principle. Contents

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1 9$nthesis

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2 :ses

•

) h$siolo%$

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4 9ee also

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; ternal lin!s

9$nthesis [edit] henolphthalein is s$nthesi7ed $ condensation of phthalic anh$dride with two e6ui3alents of phenol under acidic conditions ,hence the name-. #t was disco3ered in 1?1 $ @dolf 3on Aae$er .[2][)][4]

:ses[edit] Phenolphthalein  ,pH indicator below pH 8.2

colorless

between pH 10.0 and 13.0   ⇌

 

fuchsia

henolphthalein has een used for o3er a centur$ as a laati3e ut is now ein% remo3ed from o3erthe counter laati3es[;] ecause of concerns o3er carcino%enicit$.[=][?] henolphthalein is used in a test to identif$ sustances that are thou%ht to e or to contain lood. 'his test is commonl$ !nown as the Bastlee$er test. @ dr$ sample is collected with a swa or filter paper.

Dirst a few drops of alcohol then a few drops of phenolphthalein and finall$ a few drops of h$dro%en peroide are dripped onto the sample. #f the sample contains hemo%loin it will turn pin!. 'his is considered a positi3e test and indicates that the sample contains hemo%loin and therefore is li!el$ lood. 'his test is nondestructi3e to the sampleE it can e !ept and used in further tests at the la. 'his test has the same reaction with lood from an$ animal so further testin% would e re6uired to determine whether it ori%inates from a human. henolphthalein is used in to$s for eample as a component of disappearin% in!s or disappearin% d$e on the Hollywood Hair Aarie hair. #n the in! it is mied with sodium h$droide which reacts with caron dioide in the air. 'his reaction leads to the pH fallin% elow the color chan%e threshold as h$dro%en ions are released 3ia the reaction( OH+ ,a6- * CO2 ,%- F CO)2+ ,a6- * H* ,a6'o de3elop the hair and "ma%ic" %raphical patterns the in! is spra$ed with a solution of h$droide which leads to the appearance of the hidden %raphics $ the same mechanism descried ao3e for color chan%e in al!aline solution. 'he pattern will e3entuall$ disappear $ the same reaction with caron dioide detailed ao3e. 'h$molphthalein is used for the same purpose and in the same wa$ when lue color is desired.[] henolphthalein is used as an acid or ase indicator where in contact or presence of acid it will turn colorless and with ase it will turn into a pin!ish 3iolet color. #t is also a component in uni3ersal indicator  a solution consistin% of a miture of pH indicators,usuall$ phenolphthalein meth$l red romoth$mol lue and th$mol lue-.[G] 'he acidase indication ailities of phenolphthalein also ma!e it useful for testin% for si%ns of caronation reactions in concrete. Concrete has naturall$ hi%h pH due to the calcium h$droide formed when ortland cement reacts with water. 'he pH of the ionic water solution present in the pores of fresh concrete ma$ e o3er 14. ormal caronation of concrete occurs as the cement h$dration products in concrete react with caron dioide in the atmosphere and can reduce the pH to I to G althou%h that reaction usuall$ is restricted to a thin la$er at the surface. 5hen a 1J phenolphthalein solution is applied to normal concrete it will turn ri%ht pin!. #f the concrete ha s under%one caronation no color chan%e will e oser3ed