Question

Which of the following solution will turn phenolphthalein Pink?

(a) HCl(aq) (b) CO2(aq) (c) KOH (aq) (d) H2SO4 (aq)​

Answer 1

LiOH is a base and will turn the colour of phenolphthalein pink. Lime water is a calcium hydroxide solution, Ca(OH)2, which is a base. Lime water was added to the regular water in the solution. Lime water is a base, so when the phenolphthalein was added to the solution, it turned the solution pink.

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Answer 2

The correct option is- (c) KOH (aq).

• Phenolphthalein is a synthetic indicator that is used in acid-base titrations. If it is added to an acidic or neutral solution, the solution will turn colourless. The addition of phenolphthalein to a basic solution will turn it pink due to the formation of phenolphthalein ions.
• As KOH (potassium hydroxide) is a base, the addition of phenolphthalein to its solution will change its colour to pink.
• On the other hand, all the other solutions are acidic, they will turn colourless when phenolphthalein is added.