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The discovery of phenolphthalein's laxative effect was due to an attempt by the Hungarian government to label [clarification needed] genuine local white wine with the substance in 1900. Phenolphthalein did not change the taste of the wine and would change color when a base is added, making it a good label in principle.
It is a weak acid with pK a = 8.00 at 20 °C (68 °F). A solution of phenol red is used as a pH indicator, often in cell culture. Its color exhibits a gradual transition from yellow (λ max = 443 nm [2]) to red (λ max = 570 nm [3]) over the pH range 6.8 to 8.2. Above pH 8.2, phenol red turns a bright pink color. [4] [5]
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.
For optimal accuracy, the color difference between the two species should be as clear as possible, and the narrower the pH range of the color change the better. In some indicators, such as phenolphthalein, one of the species is colorless, whereas in other indicators, such as methyl red, both species confer a color. While pH indicators work ...
In most cases, these substance changes color when mixed with an acid or base. Phenolphthalein, commonly used as a pH indicator, turns pink in the presence of a base such as ammonia fumes or sodium carbonate. Vinegar, is revealed by red cabbage water [12] Vinegar contains acetic acid that affects the pH indicator in red cabbage water. Vinegar ...
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]
Calcium hydroxide has a high enough pH to turn the phenolphthalein a vivid purplish-pink color, thus indicating the presence of water. Chemical pulping : Calcium oxide is used to make calcium hydroxide , which is used to regenerate sodium hydroxide from sodium carbonate in the chemical recovery at kraft pulp mills.
Phenolphthalein does indeed turn orange in very strong acid solutions (hydronium > 10M). Have a chemistry teacher put some full strength sulfuric acid in a small beaker (do this in a fume hood), and add a few drops of the indicator. It will turn orange. — ★ Parsa ☞ talk 21:53, 1 May 2013 (UTC)