Editing Universal indicator (section)

== Composition ==

A universal indicator is usually composed of [[water]], [[1-propanol]], [[phenolphthalein]], [[sodium hydroxide]], [[methyl red]], [[bromothymol blue]], [[sodium bisulfite]], and [[thymol blue]].<ref>{{ 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 }}</ref> 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, colours blue to violet indicate an alkaline solution and a green colour indicates that a solution is neutral.

{| class="wikitable"
|+ Universal indicator components<ref>{{cite book |last1=Jenkins |first1=Glenn Llewellyn |title=Jenkins' Quantitative Pharmaceutical Chemistry |date=1979 |publisher=Mei Ya |page=67 |url=https://www.google.com.ph/books/edition/Jenkins_Quantitative_Pharmaceutical_Chem/QPaFoAEACAAJ?hl=en |access-date=4 May 2025 |language=en}}</ref>
! Indicator
! Low pH colour
! Transition pH range
! High pH colour
|-
| [[Thymol blue]] (first transition)
| style="background:red; color:white"| Red
| style="text-align:center;"| 1.2&nbsp;–&nbsp;2.8
| style="background:yellow;"| Yellow
|-
| [[Methyl orange]]
| style="background:red; color:white"|Red
| style="text-align:center;"| 3.2&nbsp;–&nbsp;4.4
| style="background:yellow;"| Yellow
|-
| [[Methyl red]]
| style="background:red; color:white"| Red
| style="text-align:center;"| 4.8&nbsp;–&nbsp;6.0
| style="background:yellow; color:black"|Yellow
|-
| [[Bromothymol blue]]
| style="background:yellow;"| Yellow
| style="text-align:center;"| 6.0&nbsp;–&nbsp;7.6
| style="background:blue; color:white"| Blue
|-
| [[Thymol blue]] (second transition)
| style="background:yellow;"| Yellow
| style="text-align:center;"| 8.0&nbsp;–&nbsp;9.6
| style="background:blue; color:white"| Blue
|-
| [[Phenolphthalein]]
| Colourless
| style="text-align:center;"| 8.3&nbsp;–&nbsp;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.