Phenolphthalein

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Phenolphthalein is a chemical compound with the formula C ₂₀ H ₁₄ O ₄ and is often written as " HIn "or" phph "in short notation. Phenolphthalein is often used as an indicator in acid-base titration. For this application, it turns out to be colorless in acid and pink solutions in the base solution. That includes a dye class known as Pthalein dye.

Phenolphthalein is slightly soluble in water and is usually dissolved in alcohol for use in experiments. It is a weak acid, which can lose H ions in solution. The phenolphthalein molecule is colorless, and the phenolphthalein ion is pink. When a base is added to phenolphthalein, a molecule? the equilibrium ion shifts to the right, leading to more ionization because the H ion is removed. This is predicted by the Le Chatelier principle.

Common use Phenolphthalein is an indicator of acid-base titration. It also serves as a universal indicator component, along with methyl red, bromothymol blue, and blue thymol.

Phenolphthalein adopts four different states in aqueous solution: Under very strong acid conditions, it exists in protonated form (HIn ), giving it an orange color. Between very acidic and slightly basic conditions, the lactone (HIn) is colorless. Double-deprotonated forms (in ^{2 -} ) (phenolic anion shapes) provide a familiar pink color. In a very basic solution, the pink color of phenolphthalein undergoes a somewhat slower fading reaction and becomes completely colorless above 13.0 pH. A slightly dull reaction that produces a colorless In (OH) ^{3 -} ion is sometimes used in the class to study reaction kinetics.

Phenolphthalein pH Sensitivity is exploited in other applications: Concrete has a high natural pH because calcium hydroxide is formed when Portland cement reacts with water. When the concrete reacts with carbon dioxide in the atmosphere, the pH decreases to 8.5-9. When a 1% phenolphthalein solution is applied to normal concrete, the color becomes bright pink. However, if it remains colorless, it indicates that the concrete has been carbonated. In similar applications, spackling is used to repair holes in drywall containing phenolphthalein. When applied, the base material maintains a pink color; when spackling has healed by reaction with atmospheric carbon dioxide, the pink color fades.

Phenolphthalein is used in toys, for example as a missing ink component, or the disappearance of a dye on Hollywood Hair Barbie hair. In ink, it is mixed with sodium hydroxide, which reacts with carbon dioxide in the air. This reaction causes the pH to fall below the color change threshold when the hydrogen ions are released by the reaction:

OH ^- _(aq) CO _{2 (g)} -> CO ^{2 -}