A substance dissolves in water, turns red litmus blue, and gives carbon dioxide with acid. Which substance could it be?
Answer and explanation
Correct answer: Sodium carbonate
The governing concept is the identification of a basic carbonate salt by two tests. Turning red litmus blue shows that the aqueous solution is basic. Releasing carbon dioxide on adding an acid is characteristic of a carbonate or hydrogen carbonate: CO₃²⁻ + 2H⁺ → CO₂ + H₂O. Sodium carbonate dissolves in water, gives an alkaline solution through hydrolysis, and produces carbon dioxide with acids. Thus option B fits both observations; sodium chloride is neutral, while ammonium chloride and copper sulfate do not give this combination.
Frequently asked questions
What is the correct answer to this question?
Sodium carbonate
Why is this the correct answer?
The governing concept is the identification of a basic carbonate salt by two tests. Turning red litmus blue shows that the aqueous solution is basic. Releasing carbon dioxide on adding an acid is characteristic of a carbonate or hydrogen carbonate: CO₃²⁻ + 2H⁺ → CO₂ + H₂O. Sodium carbonate dissolves in water, gives an alkaline solution through hydrolysis, and produces carbon dioxide with acids. Thus option B fits both observations; sodium chloride is neutral, while ammonium chloride and copper sulfate do not give this combination.
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.
