Phenolphthalein: Difference between revisions

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{{Short description|pH indicator that turns pink in basic solution}}

[[Image:Phenophthalein.png|frame|right|Illustration of bond structure of phenolphthalein]]

{{About|Phenolphthalein|other related dyes in the phthalein family|Phthalein dye}}

{{chembox

| Verifiedfields = changed

| Watchedfields = changed

| verifiedrevid = 408953309

| ImageFile = Phenolphthalein.svg

| ImageClass = skin-invert

| ImageFile2 = Sample of solid phenolphthalein.jpg

| ImageSize2 = 250px

| PIN = 3,3-Bis(4-hydroxyphenyl)-2-benzofuran-1(3''H'')-one

| OtherNames = 3,3-Bis(4-hydroxyphenyl)isobenzofuran-1(3''H'')-one

| Section1 = {{Chembox Identifiers

|UNII_Ref = {{fdacite|changed|FDA}}

|UNII = 6QK969R2IF

|ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

|ChemSpiderID = 4600

|InChI = 1/C20H14O4/c21-15-9-5-13(6-10-15)20(14-7-11-16(22)12-8-14)18-4-2-1-3-17(18)19(23)24-20/h1-12,21-22H

|InChIKey = KJFMBFZCATUALV-UHFFFAOYAH

|ChEMBL_Ref = {{ebicite|correct|EBI}}

|ChEMBL = 63857

|StdInChI_Ref = {{stdinchicite|correct|chemspider}}

|StdInChI = 1S/C20H14O4/c21-15-9-5-13(6-10-15)20(14-7-11-16(22)12-8-14)18-4-2-1-3-17(18)19(23)24-20/h1-12,21-22H

|StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}

|StdInChIKey = KJFMBFZCATUALV-UHFFFAOYSA-N

|CASNo=77-09-8

|CASNo_Ref = {{cascite|correct|CAS}}

|PubChem = 4764

|KEGG_Ref = {{keggcite|correct|kegg}}

|KEGG = D05456

|DrugBank_Ref = {{drugbankcite|changed|drugbank}}

|DrugBank = DB04824

|SMILES = O=C1OC(C2=C1C=CC=C2)(C3=CC=C(C=C3)O[H])C4=CC=C(C=C4)O[H]

}}

| Section2 = {{Chembox Properties

|C=20 | H=14 | O=4

|Appearance = White powder

|Density = 1.277 g/cm³ ({{convert|32|C}})

|MeltingPtC = 258-263

|MeltingPt_ref = <ref name="sigma">{{cite web|url=https://www.sigmaaldrich.com/catalog/product/sial/105945|title=Phenolphthalein|access-date=7 October 2014|archive-date=8 November 2015|archive-url=https://web.archive.org/web/20151108081633/http://www.sigmaaldrich.com/catalog/product/sial/105945|url-status=live}}</ref>

|Solubility = 400 mg/l

|Solvent = other solvents

|SolubleOther = Insoluble in benzene and hexane; very soluble in ethanol and ether; slightly soluble in DMSO

|LambdaMax = 552 nm (1st)<br> 374 nm (2nd)<ref name="sigma" />

}}

| Section6 = {{Chembox Pharmacology

|ATCCode_prefix = A06

|ATCCode_suffix = AB04

}}

| Section7 = {{Chembox Hazards

|GHSPictograms = {{GHS08}}<ref name="sigma" />

|GHSSignalWord = Danger

|HPhrases = {{H-phrases|341|350|361}}<ref name="sigma" />

|PPhrases = {{P-phrases|201|281|308+313}}<ref name="sigma" />

|NFPA-H = 2

|NFPA-F = 3

|NFPA-R = 0

}}

}}

'''Phenolphthalein''' ({{IPAc-en|f|ɛ|ˈ|n|ɒ|l|(|f|)|θ|ə|l|iː|n}}{{cn|date=June 2022}} {{Respell|feh|NOL(F)|thə|leen}}) is a [[chemical compound]] with the [[chemical formula|formula]] [[carbon|C]]₂₀[[hydrogen|H]]₁₄[[oxygen|O]]₄ and is often written as "'''HIn'''", "'''HPh'''", "'''phph'''" or simply "'''Ph'''" in shorthand notation. Phenolphthalein is often used as an indicator in [[acid–base titration]]s. For this application, it turns colorless in [[acid]]ic solutions and pink in [[base (chemistry)|basic]] solutions. It belongs to the class of dyes known as [[phthalein dyes]].

[[Image:Titration.png|frame|left|Rough illustration of a titration with phenol&shy;phthalein prior to the [[endpoint]]]]

Phenolphthalein is slightly soluble in [[water]] and usually is dissolved in [[Alcohol (chemistry)|alcohol]]s in [[experiment]]s. It is a weak acid, which can lose [[Hydrogen ion|H⁺ ion]]s in solution. The nonionized phenolphthalein molecule is colorless and the double deprotonated phenolphthalein ion is [[Fuchsia (color)|fuchsia]]. Further addition of hydroxide in higher pH occurs slowly and leads to a colorless form, since the conjugated system is broken.<ref name=Tamura1996 /> Phenolphthalein in concentrated [[sulfuric acid]] is orange-red due to protonation and creation of a stabilised [[Triphenylcarbenium|trityl cation]].

'''Phenolphthalein''' is a sensitive [[pH]] [[pH indicator|indicator]] with the formula C₂₀H₁₄O₄. Often used in [[titration]]s, it turns from colorless in [[acid]]ic solutions to pink in [[base (chemistry)|basic]] solutions, the color change occurring between pH 8 and pH 10. If the concentration of indicator is particularly strong, it can appear purple.

==Uses==

In strongly basic solutions, phenolphthalein's pink color undergoes a rather slow fading reaction and becomes colorless again. In other words, the molecule has three forms:

===pH indicator===

{{pH_indicator|indicator_name=Phenolphthalein |low_pH=8.3 |high_pH=10.0|low_pH_color=white|low_pH_text=black|high_pH_color=magenta|high_pH_text=white}}

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]].<ref>{{cite encyclopedia|url=https://www.iscid.org/encyclopedia/Universal_Indicator |title=Universal Indicator |encyclopedia=ISCID Encyclopedia of Science and Philosophy |url-status=dead |archive-url=https://web.archive.org/web/20060925035727/https://www.iscid.org/encyclopedia/Universal_Indicator |archive-date=September 25, 2006}}</ref>

Phenolphthalein adopts different forms in aqueous solution depending on the pH of the solution.<ref name=wittke1983>{{cite journal |last1=Wittke |first1=Georg |title=Reactions of phenolphthalein at various pH values |journal=Journal of Chemical Education |date=1 March 1983 |volume=60 |issue=3 |pages=239 |doi=10.1021/ed060p239 |bibcode=1983JChEd..60..239W |issn=0021-9584}}</ref><ref name=Tamura1996>{{cite journal |last1=Tamura |first1=Zenzo |title=Spectrophotometric Analysis of the Relationship between Dissociation and Coloration, and of the Structural Formulas of Phenolphthalein in Aqueous Solution |journal=Analytical Sciences |date= December 1996 |volume=12 |issue=6 |pages=927–930 |doi=10.2116/analsci.12.927|doi-access=free }}</ref><ref name=Abdel-Hamid>{{cite journal |last1=Abdel-Hamid |first1=Refat |title=The Adsorption Behavior of Phenolphthalein at a Mercury Electrode in Water-Ethanol Solutions |journal=Monatshefte für Chemie - Chemical Monthly |date=1 September 1998 |volume=129 |issue=8 |pages=817–826 |doi=10.1007/PL00013491|s2cid=92339258 }}</ref><ref name=Kunimoto2001>{{cite journal |last1=Kunimoto |first1=Ko-Ki |title=Molecular structure and vibrational spectra of phenolphthalein and its dianion |journal=Spectrochimica Acta Part A |date= February 2001|volume=57 |issue=2 |pages=265–271 |doi=10.1016/S1386-1425(00)00371-1|pmid=11206560 |bibcode=2001AcSpA..57..265K }}</ref> Inconsistency exists in the literature about hydrated forms of the compounds and the color of sulfuric acid. Wittke reported in 1983 that it exists in protonated form (H₃In⁺) under strongly acidic conditions, providing an orange coloration.

<table style="margin-left:auto; margin-right:auto;">

<tr>

<td align="center">H₂Phenolphthalein <br> acidic <br> no color

<td align="center">&harr;

<td align="center"> Phenolphthalein^2- <br> basic <br> pink

<td align="center"> &harr;

<td align="center"> Phenolphthalein(OH)^3- <br> strong alkaline <br> no color

</table>

The lactone form (H₂In) is colorless and dominates between strongly acidic and slightly basic conditions. The doubly deprotonated (In^2-) phenolate form (the [[anion]] form of phenol) gives the familiar pink color. In strongly basic solutions, phenolphthalein is converted to its In(OH)³⁻ form, and its pink color undergoes a rather slow fading reaction<ref name=Kunimoto2001 /> and becomes completely colorless when pH is greater than 13.

The fading reaction is sometimes used in undergraduate classes for the study of reaction kinetics.<br>

The [[pKa|p''K''_a]] values of phenolphthalein were found to be 9.05, 9.50 and 12 while those of phenolsulfonphthalein are 1.2 and 7.70. The p''K''_a for the color change is 9.50.<ref name=Tamura1996 />

Phenolphthalein is insoluble in [[water]], and is usually dissolved in [[alcohol]]s for use in [[experiment]]s. It is itself a weak acid, which can lose H⁺ ions in solution. The phenolphthalein molecule is colorless. However, the phenolphthalein ion is pink. When a base is added to the phenolphthalein, the atom &harr; ions equilibrium shifts to the ionization because H⁺ ions are removed, (by [[Le Chatelier's principle]]).<br>

{| class="wikitable" style="margin: 1em auto 1em auto; text-align: center;"

&nbsp;<br>

! Species

| H₃In⁺ || H₂In || In²⁻ || In(OH)³⁻

|-

! Structure

| [[File:Phenolphthalein-very-low-pH-2D-skeletal.svg|class=skin-invert-image|100px]] || [[File:Phenolphthalein-low-pH-2D-skeletal.svg|class=skin-invert-image|80px]] || [[File:Phenolphthalein-mid-pH-2D-skeletal.svg|class=skin-invert-image|80px]] || [[File:Phenolphthalein-high-pH-2D-skeletal.svg|class=skin-invert-image|80px]]

|-

! Model

| [[File:Phenolphthalein-orange-very-low-pH-3D-balls.png|80px]] || [[File:Phenolphthalein-colourless-low-pH-3D-balls.png|80px]] || [[File:Phenolphthalein-red-mid-pH-3D-balls.png|80px]] || [[File:Phenolphthalein-colourless-high-pH-3D-balls.png|80px]]

|-

! pH

| <−1 in H₂SO₄<ref name=wittke1983 /> || 0–8.3 || 8.3–10.0<ref>{{cite journal |last1=Rathod |first1=Balraj B. |last2=Murthy |first2=Sahana |last3=Bandyopadhyay |first3=Subhajit |title=Is this Solution Pink Enough? A Smartphone Tutor to Resolve the Eternal Question in Phenolphthalein-Based Titration |journal=Journal of Chemical Education |date=20 February 2019 |volume=96 |issue=3 |pages=486–494 |doi=10.1021/acs.jchemed.8b00708|bibcode=2019JChEd..96..486R |s2cid=104475433 }}</ref> || >12

|-

! Conditions

| strongly acidic || acidic or near-neutral || basic || strongly basic

|-

! Color

| orange || colorless || pink to fuchsia || colorless

|-

! Image

| [[File:Phenolphthalein-in-conc-sulfuric-acid.jpg|100px]] || || [[File:Phenolphthalein-at-pH-9.jpg|100px]] ||

|}

{| class="wikitable" style="margin: 1em auto 1em auto;"

Phenolphthalein has been used for over a century as a [[laxative]], but is now being removed from the market because of concerns over [[carcinogen]]ity. However, the small amounts usually used in experiments are harmless. Phenolphthalein is also commonly used in a mixture, primarily by forensic scientists, to test for the presence of blood.

|-

| [[File:Phenolphthalein reaction.gif|PP startAnimGif]]

|-

| An animation of the pH-dependent reaction mechanism: H₃In⁺ → H₂In → In²⁻ → In(OH)³⁻

|}

====Carbonation of concrete====

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, some [[spackling]] used to repair holes in drywall contains phenolphthalein. When applied, the basic spackling material retains a pink color; when the spackling has cured by reaction with atmospheric carbon dioxide, the pink color fades.<ref>{{cite patent | country = US | number = 6531528 | title = Ready to use spackle/repair product containing dryness indicator | pubdate = 2003-03-11 | inventor = Ronald D. Kurp | assign = Dap Products Inc.}}</ref>

====Education====

In a highly basic solution, phenolphthalein's slow change from pink to colorless as it is converted to its Ph(OH)³⁻ form is used in chemistry classes for the study of [[reaction kinetics]].

====Entertainment====

Phenolphthalein is used in toys, for example as a component of disappearing inks, or disappearing dye on the "Hollywood Hair" [[Barbie]] hair. In the ink, it is mixed with [[sodium hydroxide]], which reacts with carbon dioxide in the air. This reaction leads to the pH falling below the color change threshold as hydrogen ions are released by the reaction:

:[[hydroxide|OH⁻]]_{[[aqueous|(aq)]]} + [[carbon dioxide|CO₂]]_[[gas|(g)]] → [[carbonate|{{chem|CO|3|2−}}]]_(aq) + [[proton|H⁺]]_(aq).

To develop the hair and "magic" graphical patterns, the ink is sprayed with a solution of hydroxide, which leads to the appearance of the hidden graphics by the same mechanism described above for color change in alkaline solution. The pattern will eventually disappear again because of the reaction with [[carbon dioxide]]. [[Thymolphthalein]] is used for the same purpose and in the same way, when a blue color is desired.<ref>{{Cite web |url=https://www.chymist.com/Toystore%20part3.pdf |title=Toystore |access-date=2022-02-22 |archive-date=2021-07-02 |archive-url=https://web.archive.org/web/20210702182850/http://www.chymist.com/Toystore%20part3.pdf |url-status=live }}</ref>

==== Detection of blood ====

{{main|Kastle-Meyer test}}

A reduced form of phenolphthalein, phenolphthalin, which is colorless, is used in a test to identify substances thought to contain blood, commonly known as the [[Kastle–Meyer test]]. A dry sample is collected with a swab or filter paper. A few drops of alcohol, then a few drops of phenolphthalein, and finally a few drops of [[hydrogen peroxide]] are dripped onto the sample. If the sample contains [[hemoglobin]], it will turn pink immediately upon addition of the peroxide, because of the generation of phenolphthalein. A positive test indicates the sample contains hemoglobin and, therefore, is likely blood. A false positive can result from the presence of substances with catalytic activity similar to hemoglobin. This test is not destructive to the sample; it can be kept and used in further tests. This test has the same reaction with blood from any animal whose blood contains hemoglobin, including almost all vertebrates; further testing would be required to determine whether it originated from a human.

===Laxative===

{{See also|Phenol red}}

Phenolphthalein has been used for over a century as a [[laxative]], but is now being removed from [[Over-the-counter drug|over-the-counter]] laxatives<ref>{{cite journal | pmid = 12708936 |date=May 2003 | author = Spiller, H. A. | author2 = Winter, M. L. | author3 = Weber, J. A. | author4 = Krenzelok, E. P. | author5 = Anderson, D. L. | author6 = Ryan, M. L. | title = Skin Breakdown and Blisters from Senna-Containing Laxatives in Young Children | volume = 37 | issue = 5 | pages = 636–639 | journal = The Annals of Pharmacotherapy | doi = 10.1345/aph.1C439 |s2cid=31837142 }}</ref> over concerns of [[carcinogen]]icity.<ref>{{cite journal | url = https://cancerres.aacrjournals.org/content/56/21/4922.full.pdf | journal = Cancer Research | volume = 56 | pages = 4922–4926 | date = 1996 | title = Phenolphthalein Exposure Causes Multiple Carcinogenic Effects in Experimental Model Systems | author = Dunnick, J. K. | author2 = Hailey, J. R. | pmid = 8895745 | issue = 21 | access-date = 2022-02-22 | archive-date = 2022-02-17 | archive-url = https://web.archive.org/web/20220217005030/https://cancerres.aacrjournals.org/content/56/21/4922.full.pdf | url-status = live }}</ref><ref>{{cite journal | pmid = 9544189 | date = 1998 | author = Tice, R. R. | author2 = Furedi-Machacek, M. | author3 = Satterfield, D. | author4 = Udumudi, A. | author5 = Vasquez, M. | author6 = Dunnick, J. K. | title = Measurement of Micronucleated Erythrocytes and DNA Damage during Chronic Ingestion of Phenolphthalein in Transgenic Female Mice Heterozygous for the p53 Gene | volume = 31 | issue = 2 | pages = 113–124 | journal = Environmental and Molecular Mutagenesis | doi = 10.1002/(SICI)1098-2280(1998)31:2<113::AID-EM3>3.0.CO;2-N | s2cid = 36550267 }}</ref> Laxative products formerly containing phenolphthalein have often been reformulated with alternative active ingredients: Feen-a-Mint<ref>{{Cite web|url=https://www.drugbank.ca/drugs/DB04824|website=DrugBank|title=Phenolphthalein|access-date=2020-04-25|archive-date=2020-08-06|archive-url=https://web.archive.org/web/20200806152100/https://www.drugbank.ca/drugs/DB04824|url-status=live}}</ref> switched to [[bisacodyl]], and Ex-Lax<ref>{{cite news |url= https://www.nytimes.com/1997/08/30/us/3-versions-of-ex-lax-are-recalled-after-fda-proposes-ban-on-ingredient.html |title= 3 Versions of Ex-Lax Are Recalled After F.D.A. Proposes Ban on Ingredient |first= Sheryl Gay |last= Stolberg |work= The New York Times |date= August 30, 1997 |access-date= April 25, 2020 |archive-date= May 7, 2021 |archive-url= https://web.archive.org/web/20210507041558/http://www.nytimes.com/1997/08/30/us/3-versions-of-ex-lax-are-recalled-after-fda-proposes-ban-on-ingredient.html |url-status= live }}</ref> was switched to a [[Senna glycoside|senna extract]].

[[Thymolphthalein]] is a related laxative made from [[thymol]].

Despite concerns regarding its carcinogenicity based on rodent studies, the use of phenolphthalein as a laxative is unlikely to cause [[ovarian cancer]].<ref>{{cite journal | last = Cooper | first = G. S. | author2 = Longnecker, M. P. | author3 = Peters, R. K. | title = Ovarian Cancer Risk and Use of Phenolphthalein-Containing Laxatives | journal = Pharmacoepidemiology and Drug Safety | date = 2004 | volume = 13 | issue = 1 | pages = 35–39 | pmid = 14971121 | doi = 10.1002/pds.824 | s2cid = 24783082 | url = https://zenodo.org/record/1229318 | access-date = 2019-06-26 | archive-date = 2022-01-26 | archive-url = https://web.archive.org/web/20220126210628/https://zenodo.org/record/1229318 | url-status = live }}</ref> Some studies suggest a weak association with [[colon cancer]], while others show none at all.<ref name=IARC>{{cite book |chapter=Other pharmaceutical agents. |title=IARC monographs on the evaluation of carcinogenic risks to humans |date=2000 |volume=76 |pages=345–486 |publisher=International Agency for Research on Cancer |pmid=11000977 |pmc=7196975 |url=https://www.ncbi.nlm.nih.gov/books/NBK401424/}}</ref>

Phenolphthalein is described as a stimulant laxative.<ref name=IARC/> In addition, it has been found to inhibit human cellular calcium influx via store-operated calcium entry (SOCE, see {{link section|Calcium release activated channel|Structure}}) ''in vivo''. This is effected by its inhibiting [[thrombin]] and [[thapsigargin]], two activators of SOCE that increase intracellular free calcium.<ref>{{cite journal | last = Dobrydneva | first = Y. | author2 = Wilson, E. | author3 = Abelt, C. J. | author4 = Blackmore, P. F. | title = Phenolphthalein as a Prototype Drug for a Group of Structurally Related Calcium Channel Blockers in Human Platelets | journal = Journal of Cardiovascular Pharmacology | date = 2009 | volume = 53 | issue = 3 | pages = 231–240 | pmid = 19247192 | doi=10.1097/FJC.0b013e31819b5494| s2cid = 21833487 }}</ref>

Phenolphthalein has been added to the [[European Chemicals Agency]]'s candidate list for [[substance of very high concern]] (SVHC).<ref>{{Cite web|url=https://echa.europa.eu/substance-information/-/substanceinfo/100.000.914|title=Phenolphthalein - Substance Information - ECHA|website=echa.europa.eu|language=en-GB|access-date=2017-11-06|archive-date=2018-06-12|archive-url=https://web.archive.org/web/20180612135929/https://echa.europa.eu/substance-information/-/substanceinfo/100.000.914|url-status=live}}</ref> It is on the [[IARC group 2B]] list for substances "possibly carcinogenic to humans".<ref name=KA/>

The discovery of phenolphthalein's laxative effect was due to an attempt by the Hungarian government to label{{clarify|date=June 2023}} genuine local white wine with the substance in 1900. Phenolphthalein did not change the taste of the wine and would change color when a base is added, making it a good label in principle. However, it was found that ingestion of the substance led to diarrhea. Max Kiss, a Hungarian-born pharmacist residing in New York, heard about the news and launched Ex-Lax in 1906.<ref>{{cite web |last1=May |first1=Paul |title=Phenolphthalein - Molecule of the Month - March 2022 (HTML version) |url=https://www.chm.bris.ac.uk/motm/phenolphthalein/phphh.htm |website=www.chm.bris.ac.uk}}</ref><ref name=KA>{{cite web |last1=Arney |first1=Kat |title=Phenolphthalein |url=https://www.chemistryworld.com/podcasts/phenolphthalein/3009674.article |website=Chemistry World |language=en |date=2018-10-25}}</ref>

==Synthesis==

Phenolphthalein can be synthesized by condensation of [[phthalic anhydride]] with two equivalents of [[phenol]] under acidic conditions. It was discovered in 1871 by [[Adolf von Baeyer]].<ref>{{cite journal | author = Baeyer, A. | date = 1871 | title = Ueber eine neue Klasse von Farbstoffen | journal = Berichte der Deutschen Chemischen Gesellschaft | volume = 4 | issue = 2 | pages = 555–558 | doi = 10.1002/cber.18710040209 | url = https://zenodo.org/record/1425008 | access-date = 2020-09-02 | archive-date = 2021-02-14 | archive-url = https://web.archive.org/web/20210214061740/https://zenodo.org/record/1425008 | url-status = live }}</ref><ref>{{cite journal | author = Baeyer, A. | date = 1871 | title = Ueber die Phenolfarbstoffe | journal = Berichte der Deutschen Chemischen Gesellschaft | volume = 4 | issue = 2 | pages = 658–665 | doi = 10.1002/cber.18710040247 | url = https://zenodo.org/record/1425010 | access-date = 2019-06-26 | archive-date = 2021-10-11 | archive-url = https://web.archive.org/web/20211011061658/https://zenodo.org/record/1425010 | url-status = live }}</ref><ref>{{cite journal | author = Baeyer, A. | date = 1871 | title = Ueber die Phenolfarbstoffe | journal = Polytechnisches Journal | volume = 201 | issue = 89 | pages = 358–362 | url = https://dingler.culture.hu-berlin.de/article/pj201/ar201089 | access-date = 2022-02-22 | archive-date = 2021-10-11 | archive-url = https://web.archive.org/web/20211011061700/http://dingler.culture.hu-berlin.de/article/pj201/ar201089 | url-status = live }}</ref>

[[File:Phenolphthalein Synthesis.svg|class=skin-invert-image|520px|center|thumb|Synthesis of phenolphthalein<ref>Max Hubacher, {{US patent|2192485}} (1940 to Ex Lax Inc)</ref>]]

==See also==

*[[Bromothymol blue]]

*[[Litmus]]

*[[Methyl orange]]

*[[pH indicator]]

*[[Thymolphthalexone]]

*[[Universal indicator]]

==References==

{{reflist|31em}}

Phenolphthalein is used to perform a presumptive blood test, and is commonly known as the [[Kastle-Meyer test]]. A dry sample is collected with a swab or filter paper. First a few drops of alcohol, then a few drops of phenolphthalein and finally a few drops of hydrogen peroxide are dripped onto the sample. If the sample turns pink then it is a positive test. This test is nondestructive to the sample, it can be kept and used in further tests at the lab. This test has the same reaction with human blood and animal blood so further testing would be required to determine which it is.

==External links==

{{Commons category|Phenolphthalein}}

*[http://www.chemguide.co.uk/physical/acidbaseeqia/indicators.html Page on different titration indicators, including phenolphthalein]

*[https://www.chemguide.co.uk/physical/acidbaseeqia/indicators.html Page on different titration indicators, including phenolphthalein]

*http://wwwsoc.nii.ac.jp/jsac/analsci/pdfs/a15_0611.pdf

{{Laxatives}}

[[Category: pH indicators]]

{{Purinergics}}

[[Category:1871 introductions]]

[[da:Phenolphthalein]]

[[Category:PH indicators]]

[[de:Phenolphthalein]]

[[Category:Triarylmethane dyes]]

[[es:Fenolftaleína]]

[[Category:4-Hydroxyphenyl compounds]]

[[nl:Fenolftaleïne]]

[[Category:IARC Group 2B carcinogens]]

[[ja:フェノールフタレイン]]

[[Category:Phthalides]]

[[pt:Fenolftaleína]]

[[Category:Laxatives]]

[[sv:Fenolftalein]]