The correct answer is option 3. Colourless.
Phenolphthalein is an acid-base indicator commonly used in titrations and other laboratory applications to determine the endpoint of a reaction between an acid and a base.
In acidic solutions (pH less than 7), phenolphthalein remains colorless. It is essentially transparent in the presence of excess hydrogen ions (H⁺) characteristic of acidic conditions. Therefore, when added to an acid, phenolphthalein does not exhibit any color change and stays colorless.
The color change of phenolphthalein becomes apparent as the solution transitions from acidic to neutral and then to alkaline conditions. In the presence of a base (pH greater than 7), phenolphthalein turns pink or purple, indicating the basic or alkaline nature of the solution. The specific pH at which this color change occurs is typically around 8.2 to 10.
In summary, the color change observed when phenolphthalein is added to an acid is no change; it remains colorless. The color change becomes noticeable as the solution becomes more alkaline. |
