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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]
The doubly deprotonated (In 2-) phenolate form (the anion form of phenol) gives the familiar pink color. 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 ferric chloride test is used to determine the presence of phenols in a given sample or compound (for instance natural phenols in a plant extract). Enols , hydroxamic acids , oximes, and sulfinic acids give positive results as well. [ 1 ]
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.
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.
Predicting the color of a compound can be extremely complicated. Some examples include: Cobalt chloride is pink or blue depending on the state of hydration (blue dry, pink with water) so it is used as a moisture indicator in silica gel. Zinc oxide is white, but at higher temperatures becomes yellow, returning to white as it cools.
Phenol in the Berthelot reagent can be replaced by a variety of phenolic reagents, the most common being sodium salicylate, which is significantly less toxic. [1] This has been used for blood urea nitrogen (BUN) determinations and commonly is used to determine water and soil total and ammonia-N. Replacement of phenol by 2-phenylphenol reduces interferences by a variety of soil and water ...
Corrosion of iron nail with coiled copper in medium with ferroxyl indicator. Ferroxyl indicator, or rust indicator, is a solution containing potassium hexacyanoferrate(III), phenolphthalein and sodium chloride.