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<title>Universal indicator</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Universal indicator</span></span>

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</style><div role="note" class="hatnote navigation-not-searchable">This article is about the chemical pH indicator. For the musical artists, see <a href="Universal_Indicator_(collective)" title="Universal Indicator (collective)">Universal Indicator (collective)</a>.</div>

<p>A <b>universal indicator</b> is a <a href="PH_indicator" title="PH indicator">pH indicator</a> made of a <a href="Solution_(chemistry)" title="Solution (chemistry)">solution</a> of several compounds that exhibit various smooth <a href="Color" title="Color">colour</a> changes over a wide range <a href="PH" title="PH">pH</a> values to indicate the <a href="Acid" title="Acid">acidity</a> or <a href="Alkali" title="Alkali">alkalinity</a> of solutions. A universal indicator can be in paper form or present in a form of a solution.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading2"><h2 id="History">History</h2></div>

<p>Although there are several commercially available universal pH indicators, most are a variation of a formula patented by Yamada in 1933.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading2"><h2 id="Composition">Composition</h2></div>

<p>A universal indicator is usually composed of <a href="Water" title="Water">water</a>, <a href="1-propanol" class="mw-redirect" title="1-propanol">1-propanol</a>, <a href="Phenolphthalein" title="Phenolphthalein">phenolphthalein</a>, <a href="Sodium_hydroxide" title="Sodium hydroxide">sodium hydroxide</a>, <a href="Methyl_red" title="Methyl red">methyl red</a>, <a href="Bromothymol_blue" title="Bromothymol blue">bromothymol blue</a>, <a href="Sodium_bisulfite" title="Sodium bisulfite">sodium bisulfite</a>, and <a href="Thymol_blue" title="Thymol blue">thymol blue</a>.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> The colours that indicate the pH of a solution, after adding a universal indicator, are:

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<th>pH range

</th>

<th>Description

</th>

<th>Colour

</th></tr>

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<td>≤ 3

</td>

<td>Strong acid

</td>

<td style="background:red; color:white">Red

</td></tr>

<tr>

<td>4–6

</td>

<td>Weak acid

</td>

<td style="background:darkorange">Orange or Yellow

</td></tr>

<tr>

<td>7

</td>

<td>Neutral

</td>

<td style="background:green; color:white;">Green

</td></tr>

<tr>

<td>8–10

</td>

<td>Weak alkali

</td>

<td style="background:blue; color:white;">Blue

</td></tr>

<tr>

<td>≥ 11

</td>

<td>Strong alkali

</td>

<td style="background:darkviolet; color:white">Indigo or Violet

</td></tr></tbody></table>

<p>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.

</p>

<caption>Universal indicator components<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup>

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<th>Indicator

</th>

<th>Low pH colour

</th>

<th>Transition pH range

</th>

<th>High pH colour

</th></tr>

<tr>

<td><a href="Thymol_blue" title="Thymol blue">Thymol blue</a> (first transition)

</td>

<td style="background:red; color:white">Red

</td>

<td style="text-align:center;">1.2 – 2.8

</td>

<td style="background:yellow;">Yellow

</td></tr>

<tr>

<td><a href="Methyl_orange" title="Methyl orange">Methyl orange</a>

</td>

<td style="background:red; color:white">Red

</td>

<td style="text-align:center;">3.2 – 4.4

</td>

<td style="background:yellow;">Yellow

</td></tr>

<tr>

<td><a href="Methyl_red" title="Methyl red">Methyl red</a>

</td>

<td style="background:red; color:white">Red

</td>

<td style="text-align:center;">4.8 – 6.0

</td>

<td style="background:yellow; color:black">Yellow

</td></tr>

<tr>

<td><a href="Bromothymol_blue" title="Bromothymol blue">Bromothymol blue</a>

</td>

<td style="background:yellow;">Yellow

</td>

<td style="text-align:center;">6.0 – 7.6

</td>

<td style="background:blue; color:white">Blue

</td></tr>

<tr>

<td><a href="Thymol_blue" title="Thymol blue">Thymol blue</a> (second transition)

</td>

<td style="background:yellow;">Yellow

</td>

<td style="text-align:center;">8.0 – 9.6

</td>

<td style="background:blue; color:white">Blue

</td></tr>

<tr>

<td><a href="Phenolphthalein" title="Phenolphthalein">Phenolphthalein</a>

</td>

<td>Colourless

</td>

<td style="text-align:center;">8.3 – 10.0

</td>

<td style="background:#ff33cc;; color:white">Fuchsia

</td></tr></tbody></table>

<p>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.

</p>

<div class="mw-heading mw-heading2"><h2 id="Types">Types</h2></div>

<ul><li>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 <a href="Hydrion_paper" title="Hydrion paper">Hydrion paper</a>.</li>

<li>Solution: The main components of a universal indicator, in the form of a solution, are <a href="Thymol_blue" title="Thymol blue">thymol blue</a>, <a href="Methyl_red" title="Methyl red">methyl red</a>, <a href="Bromothymol_blue" title="Bromothymol blue">bromothymol blue</a>, and <a href="Phenolphthalein" title="Phenolphthalein">phenolphthalein</a>. This mixture is important because each component loses or gains <a href="Proton" title="Proton">protons</a> depending upon the <a href="Acidity_or_alkalinity" class="mw-redirect" title="Acidity or alkalinity">acidity or alkalinity</a> 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.</li></ul>

<div class="mw-heading mw-heading2"><h2 id="Influence_on_conductivity">Influence on conductivity</h2></div>

<p>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.<sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup>

</p>

<ul><li><a href="Litmus" title="Litmus">Litmus</a></li>

<li><a href="PH_indicator" title="PH indicator">pH indicator</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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</style><cite id="CITEREFWalker2007" class="citation book cs1">Walker, Denise (2007). <a rel="nofollow" class="external text" href="https://books.google.com/books?id=nPnRO_mQymUC&pg=PA13"><i>Acids and alkalis</i></a> (1 ed.). London: Evans. p. 13. <a href="ISBN_(identifier)" class="mw-redirect" title="ISBN (identifier)">ISBN</a> <bdi>978-0-237-53002-0</bdi><span class="reference-accessdate">. Retrieved <span class="nowrap">4 June</span> 2015</span>.</cite></span>

</li>

</li>

<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><i>Chem Abstr</i>, <b>28</b>, 2258 (1934)</span>

</li>

<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><cite id="CITEREFFosterGruntfest1937" class="citation journal cs1">Foster, L. S.; Gruntfest, I. J. (1937). "Demonstration experiments using universal indicators". <i>Journal of Chemical Education</i>. <b>14</b> (6): 274. <a href="Bibcode_(identifier)" class="mw-redirect" title="Bibcode (identifier)">Bibcode</a>:<a rel="nofollow" class="external text" href="https://ui.adsabs.harvard.edu/abs/1937JChEd..14..274F">1937JChEd..14..274F</a>. <a href="Doi_(identifier)" class="mw-redirect" title="Doi (identifier)">doi</a>:<a rel="nofollow" class="external text" href="https://doi.org/10.1021%2Fed014p274">10.1021/ed014p274</a>.</cite></span>

</li>

<li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20060925035727/http://www.iscid.org/encyclopedia/Universal_Indicator">"Universal Indicator"</a>. ISCID Encyclopedia of Science and Philosophy. Archived from <a rel="nofollow" class="external text" href="http://www.iscid.org/encyclopedia/Universal_Indicator">the original</a> on September 25, 2006.</cite></span>

</li>

<li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text"><cite id="CITEREFJenkins1979" class="citation book cs1">Jenkins, Glenn Llewellyn (1979). <a rel="nofollow" class="external text" href="https://www.google.com.ph/books/edition/Jenkins_Quantitative_Pharmaceutical_Chem/QPaFoAEACAAJ?hl=en"><i>Jenkins' Quantitative Pharmaceutical Chemistry</i></a>. Mei Ya. p. 67<span class="reference-accessdate">. Retrieved <span class="nowrap">4 May</span> 2025</span>.</cite></span>

</li>

<li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external free" href="https://github.com/ddiesing/universal_indicator_conductivity/blob/main/indicator_conc_conduct.csv">https://github.com/ddiesing/universal_indicator_conductivity/blob/main/indicator_conc_conduct.csv</a></span>

</li>

</ol></div></div></div><div><div class="zim-footer">

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