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Physical and Chemical Changes — Science STD 7 — Question

Gujarat BoardEnglish MediumSTD 7SciencePhysical and Chemical Changes1 Mark
MCQ
A synthetic indicator phenolphthalein gives $...........$ colour in basic solution:
  • A
    Red
  • B
    Blue
  • ✓
    Pink
  • D
    Colorless
✓

Answer

Correct option: C.
Pink
Phenolphthalein is often used as an indicator in acid-base titrations. It turns colourless in acidic solutions and pink in basic solutions. Phenolphthalein is slightly soluble in water and usually dissolved in alcohols for use in experiments.
It is a weak acid that can lose $H^+$ ions in solution. Phenolphthalein molecule is colourless and phenolphthalein ion is pink in colour. When a base is added to phenolphthalein, the molecule turns into ions leading to more ionization as $H^+$ ions are removed.

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