Phenolphthalein (C20H14O4) is a chemical compound used as an acid-base indicator that belongs to the phthalein family. In- is the ionic form of phenolphthalein, and HIn is the molecular form. In the basic solution, the molecule loses a hydrogen ion and becomes a negative ion. When titrating weak acids with strong bases, phenolphthalein is the ideal indicator.
It's a yellowish-white to pale orange thin crystalline powder. It has a pKa value of 9.3 and the working pH range is 8.3 to 10.0. Phenolphthalein indicator is colorless in acidic conditions and forms pink color in basic conditions
Why did the color of phenolphthalein change after the addition of an acid in a basic solution?
The phenolphthalein (HIn) is weakly acidic in nature and dissociates into H+H+ and In-In ions. The concentration of In-In ions in the solution gives the solution its pink color, and since the concentration of In-In is very low in solution under acidic conditions and the concentration of H+H+ is very high, the solution is colorless.
Similarly, under basic conditions, the concentration of H+H+ ions is extremely low, while the concentration of In-In is very high, resulting in a pink-colored solution.
What happens when acid is added to phenolphthalein?
The ion of phenolphthalein is pink, and the molecule of phenolphthalein is colorless. However, when acid is added, the phenolphthalein ion converts to a phenolphthalein molecule, rendering the solution colorless.
What color does phenolphthalein turn in an acid?
Phenolphthalein is colorless in acidic solutions and purple in basic solutions. The indicator is a substance that changes color when it comes into contact with an acid or a basic.
What happens when phenolphthalein is added to distilled water?
Since pure water is neither acidic nor alkaline, there is no color change when drops of phenolphthalein are added to it. Phenolphthalein is colorless at pH 7.0, usually turning pink in alkaline solutions at pH 8.2 or higher.
Why does phenolphthalein change color when going from an acid to a basic solution?
When the pH of the solution is 8.2 or higher, the number of ions increases, causing the solution to turn pink.
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