Phenolphthalein turns pink in an aqueous solution of sodium carbonate. What is the most appropriate reason?
Answer and explanation
Correct answer: Sodium carbonate solution is basic
Sodium carbonate is a salt of a strong base, sodium hydroxide, and a weak acid, carbonic acid. Its carbonate ions hydrolyse in water and produce hydroxide ions, making the solution alkaline. Phenolphthalein is colourless in acidic or nearly neutral conditions but pink in a sufficiently basic solution. Therefore A is correct; not every salt gives a pink colour.
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What is the correct answer to this question?
Sodium carbonate solution is basic
Why is this the correct answer?
Sodium carbonate is a salt of a strong base, sodium hydroxide, and a weak acid, carbonic acid. Its carbonate ions hydrolyse in water and produce hydroxide ions, making the solution alkaline. Phenolphthalein is colourless in acidic or nearly neutral conditions but pink in a sufficiently basic solution. Therefore A is correct; not every salt gives a pink colour.
Which subject and chapter does this question cover?
This is a Class 10 Science question. Chapter: Chemical Substances – Nature and Behaviour. Topic: Acids, Bases, and Salts.
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