2018 O Level Chem P1 Q24 — Acids and Bases / pH and Indicators Solution
Question
Methylamine dissolves in water to give an alkaline solution. A few drops of Universal Indicator are added to an aqueous solution of methylamine. Which row shows the pH of the solution and the colour of the solution after the indicator has been added?
Correct answer: A
Video Solution
Explanation
Answer: A (pH greater than 7, blue). An alkaline solution has \([\text{OH}^{-}] > [\text{H}^{+}]\), so its pH is greater than 7.
Methylamine is a weak base (like ammonia), so its solution is moderately alkaline. Universal Indicator is blue in a weak alkali (green is neutral; purple is a strong alkali).
The row showing pH greater than 7 together with a blue colour is option A. Answer A.
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