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In strongly basic solutions, phenolphthalein is converted to its In(OH) 3− form, and its pink color undergoes a rather slow fading reaction [6] and becomes completely colorless when pH is greater than 13. The pK a values of phenolphthalein were found to be 9.05, 9.50 and 12 while those of phenolsulfonphthalein are 1.2 and 7.70. [2]
Upon reduction, the very intense pink color of the cationic form of phenolphthalein fades to a faint yellow color. It is this form of phenolphthalein that is present in Kastle–Meyer test kits. In order to generate the intense pink color indicative of a positive test, the reduced phenolphthalein must be oxidized back to its normal, colored form.
It is advised to check the references for photos of reaction results. [1] Reagent testers might show the colour of the desired substance while not showing a different colour for a more dangerous additive. [2]
pH indicators: a graphic view. A pH indicator is a halochromic chemical compound added in small amounts to a solution so the pH (acidity or basicity) of the solution can be determined visually or spectroscopically by changes in absorption and/or emission properties. [1]
This is an accepted version of this page This is the latest accepted revision, reviewed on 14 December 2024. For other color lists, see Lists of colors. This article relies largely or entirely on a single source. Relevant discussion may be found on the talk page. Please help improve this article by introducing citations to additional sources. Find sources: "List of colors" alphabetical ...
Color after high pH conditions Methyl Orange Orange/red 3.1 - 4.4 Yellow Methyl Red Red 4.4 - 6.3 Yellow Congo Red Blue 3.0 - 5.2 Red Phenolphthalein Colourless 8.3 - 10.0 Pink Thymolphthalein Colourless 9.3 - 10.5 Blue Bromophenol Blue Yellow 3.0 - 4.6 Blue Bromocresol Green Yellow 3.8 - 5.6 Blue Thymol Blue Red 1.2 - 2.8; 8.0 - 9.6 Blue
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Colorants (both dyes and pigments) are listed using a dual classification which use the Colour Index Generic Name (the prime identifier) and Colour Index Constitution Numbers. These numbers are prefixed with C.I. or CI, for example, C.I. Acid Orange 7 or C.I. 15510. (This abbreviation is sometimes mistakenly thought to be CL, due to the font ...