# Universal indicator > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Universal_indicator > Markdown URL: https://mediated.wiki/source/Universal_indicator.md > Source: https://en.wikipedia.org/wiki/Universal_indicator > Source revision: 1324155086 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{Short description|Indicator that works over a wide range of pH}} {{About|the chemical pH indicator|the musical artists|Universal Indicator (collective)}} thumb|A roll of universal indicator paper thumb|Colors of universal indicator A '''universal indicator''' is a [pH indicator](/source/pH_indicator) made of a [solution](/source/Solution_(chemistry)) of several compounds that exhibit various smooth [colour](/source/Color) changes over a wide range [pH](/source/pH) values to indicate the [acidity](/source/Acid) or [alkalinity](/source/Alkali) of solutions. A universal indicator can be in paper form or present in a form of a solution.{{cite book|last1=Walker|first1=Denise|title=Acids and alkalis|date=2007|publisher=Evans|location=London|isbn=978-0-237-53002-0|page=13|edition=1|url=https://books.google.com/books?id=nPnRO_mQymUC&pg=PA13 |access-date=4 June 2015}} == History == Although there are several commercially available universal pH indicators, most are a variation of a formula patented by Yamada in 1933.''Jap. Pat.'' 99,664, Feb 21, 1933''Chem Abstr'', '''28''', 2258 (1934){{Cite journal | doi = 10.1021/ed014p274| title = Demonstration experiments using universal indicators| journal = Journal of Chemical Education| volume = 14| issue = 6| pages = 274| year = 1937| last1 = Foster | first1 = L. S. | last2 = Gruntfest | first2 = I. J. | bibcode = 1937JChEd..14..274F}} == Composition == A universal indicator is usually composed of [water](/source/water), [1-propanol](/source/1-propanol), [phenolphthalein](/source/phenolphthalein), [sodium hydroxide](/source/sodium_hydroxide), [methyl red](/source/methyl_red), [bromothymol blue](/source/bromothymol_blue), [sodium bisulfite](/source/sodium_bisulfite), and [thymol blue](/source/thymol_blue).{{ cite web | url = http://www.iscid.org/encyclopedia/Universal_Indicator | title = Universal Indicator | archiveurl = https://web.archive.org/web/20060925035727/http://www.iscid.org/encyclopedia/Universal_Indicator | archivedate = September 25, 2006 | publisher = ISCID Encyclopedia of Science and Philosophy }} The colours that indicate the pH of a solution, after adding a universal indicator, are: {| class=wikitable ! pH range ! Description ! Colour |- |≤ 3 |Strong acid | style="background:red; color:white" |Red |- |4–6 |Weak acid | style="background:darkorange" |Orange or Yellow |- |7 |Neutral | style="background:green; color:white;" |Green |- |8–10 |Weak alkali | style="background:blue; color:white;" |Blue |- |≥ 11 |Strong alkali | style="background:darkviolet; color:white" |Indigo or Violet |} The colors from yellow to red indicate an acidic solution, colors blue to violet indicate an alkaline solution and a green colour indicates that a solution is neutral. {| class="wikitable" |+ Universal indicator components{{cite book |last1=Jenkins |first1=Glenn Llewellyn |title=Jenkins' Quantitative Pharmaceutical Chemistry |date=1979 |publisher=Mei Ya |page=67 |url=https://books.google.com/books?id=QPaFoAEACAAJ |access-date=4 May 2025 |language=en}} ! Indicator ! Low pH colour ! Transition pH range ! High pH colour |- | [Thymol blue](/source/Thymol_blue) (first transition) | style="background:red; color:white"| Red | style="text-align:center;"| 1.2 – 2.8 | style="background:yellow;"| Yellow |- | [Methyl orange](/source/Methyl_orange) | style="background:red; color:white"|Red | style="text-align:center;"| 3.2 – 4.4 | style="background:yellow;"| Yellow |- | [Methyl red](/source/Methyl_red) | style="background:red; color:white"| Red | style="text-align:center;"| 4.8 – 6.0 | style="background:yellow; color:black"|Yellow |- | [Bromothymol blue](/source/Bromothymol_blue) | style="background:yellow;"| Yellow | style="text-align:center;"| 6.0 – 7.6 | style="background:blue; color:white"| Blue |- | [Thymol blue](/source/Thymol_blue) (second transition) | style="background:yellow;"| Yellow | style="text-align:center;"| 8.0 – 9.6 | style="background:blue; color:white"| Blue |- | [Phenolphthalein](/source/Phenolphthalein) | Colourless | style="text-align:center;"| 8.3 – 10.0 | style="background:#ff33cc; color:white"| Fuchsia |} Wide-range pH test papers with distinct colours for each pH from 1 to 14 are also available. Colour matching charts are supplied with the specific test strips purchased. == Types == * Paper form: It is a strip of coloured paper which changes colour to red if the solution is acidic and to blue, if the solution is basic. The strip can be placed directly onto a surface of a wet substance or a few drops of the solution can be dropped onto the universal indicator using dropping equipment. If the test solution is of a dark colour, it is preferable to use a paper universal indicator, such as [Hydrion paper](/source/Hydrion_paper). * Solution: The main components of a universal indicator, in the form of a solution, are [thymol blue](/source/thymol_blue), [methyl red](/source/methyl_red), [bromothymol blue](/source/bromothymol_blue), and [phenolphthalein](/source/phenolphthalein). This mixture is important because each component loses or gains [proton](/source/proton)s depending upon the [acidity or alkalinity](/source/acidity_or_alkalinity) of the solution being tested. It is beneficial to use this type of universal indicator in a colorless solution. This will increase the accuracy level of indication. == Influence on conductivity == thumb|Influence of universal indicator solution on the conductivity of desalinated water The impact of an ethanol-based universal indicator may seem negligible at first glance. However, in the case of dilute solutions prepared with bidistilled water, this influence becomes readily discernible and measurable.{{cite web | title=Universal_indicator_conductivity/Indicator_conc_conduct.CSV at main · ddiesing/Universal_indicator_conductivity | website=[GitHub](/source/GitHub) | url=https://github.com/ddiesing/universal_indicator_conductivity/blob/main/indicator_conc_conduct.csv }} == See also == * [Litmus](/source/Litmus) * [pH indicator](/source/pH_indicator) == References == {{refs}} Category: PH indicators --- Adapted from the Wikipedia article [Universal indicator](https://en.wikipedia.org/wiki/Universal_indicator) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Universal_indicator?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.