Editing PH indicator (section)

{{Short description|Chemical added to show pH of a solution}}{{lowercase|title=pH indicator}}
{{Acids and bases}}

[[File:Acid-base-indicators.png|thumb|pH indicators: a graphic view]]
A '''pH indicator''' is a [[halochromism|halochromic]] [[chemical compound]] added in small amounts to a [[Solution (chemistry)|solution]] so the [[pH]] ([[acid]]ity or [[Base (chemistry)|basicity]]) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties.<ref name=":0">{{Cite book |last=Harris |first=Daniel C. |url=https://www.worldcat.org/oclc/54073810 |title=Exploring chemical analysis |date=2005 |publisher=W.H. Freeman |isbn=0-7167-0571-0 |edition=3rd |location=New York |oclc=54073810}}</ref> Hence, a pH indicator is a [[Chemical substance|chemical]] detector for [[hydronium]] ions (H<sub>3</sub>O<sup>+</sup>) or hydrogen ions (H<sup>+</sup>) in the [[Acid-base reaction theories|Arrhenius model]].

Normally, the indicator causes the [[color]] of the solution to change depending on the pH. Indicators can also show change in other physical properties; for example, olfactory indicators show change in their [[odor]]. The pH value of a neutral solution is 7.0 at 25°C ([[Standard conditions for temperature and pressure#Standard laboratory conditions|standard laboratory conditions]]). Solutions with a pH value below 7.0 are considered acidic and solutions with pH value above 7.0 are basic. Since most naturally occurring [[Organic compound|organic compounds]] are weak [[Electrolyte|electrolytes]], such as [[carboxylic acid]]s and [[amine]]s, pH indicators find many applications in [[biology]] and [[analytical chemistry]]. Moreover, pH indicators form one of the three main types of indicator compounds used in chemical analysis. For the [[Quantitative analysis (chemistry)|quantitative analysis]] of metal cations, the use of [[complexometric indicator]]s is preferred,<ref>{{cite book |last1=Schwarzenbach |first1=Gerold |translator-last=Irving |translator-first=Harry |title=Complexometric Titrations |date=1957 |publisher=[[Methuen & Co]] |location=London |pages=29–46 |edition=1st English}}</ref><ref>{{cite book |last1=West |first1=T.&nbsp;S. |title=Complexometry with EDTA and related reagents |date=1969 |publisher=[[BDH Chemicals|BDH Chemicals Ltd.]] |location=Poole, UK |pages=14–82 |edition=3rd}}</ref> whereas the third compound class, the [[redox indicator]]s, are used in [[redox titration]]s ([[titration]]s involving one or more redox reactions as the basis of chemical analysis).