If sodium hydroxide solution is left exposed to air, which substance may form over time?
Answer and explanation
Correct answer: Sodium carbonate
Atmospheric air contains carbon dioxide, an acidic oxide. Sodium hydroxide absorbs it and reacts to form sodium carbonate: 2NaOH + CO₂ → Na₂CO₃ + H₂O. Continued exposure can therefore change the composition and reduce the purity of the sodium hydroxide solution. No source of nitrate, sulphide or phosphate is present, so sodium carbonate, option A, is correct.
Frequently asked questions
What is the correct answer to this question?
Sodium carbonate
Why is this the correct answer?
Atmospheric air contains carbon dioxide, an acidic oxide. Sodium hydroxide absorbs it and reacts to form sodium carbonate: 2NaOH + CO₂ → Na₂CO₃ + H₂O. Continued exposure can therefore change the composition and reduce the purity of the sodium hydroxide solution. No source of nitrate, sulphide or phosphate is present, so sodium carbonate, option A, is correct.
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.
