Why can sodium hydroxide pellets become wet and later impure in open air?
Answer and explanation
Correct answer: They absorb moisture and can form carbonate with carbon dioxide
Sodium hydroxide is deliquescent, meaning that solid NaOH absorbs water vapour from humid air and may dissolve in the absorbed moisture; this explains why pellets become wet. It also reacts with acidic carbon dioxide in air: 2NaOH + CO₂ → Na₂CO₃ + H₂O. Formation of sodium carbonate changes the composition and lowers the purity of the stored hydroxide. Thus option A correctly explains both observations. The other options describe impossible transformations under ordinary open-air conditions.
Frequently asked questions
What is the correct answer to this question?
They absorb moisture and can form carbonate with carbon dioxide
Why is this the correct answer?
Sodium hydroxide is deliquescent, meaning that solid NaOH absorbs water vapour from humid air and may dissolve in the absorbed moisture; this explains why pellets become wet. It also reacts with acidic carbon dioxide in air: 2NaOH + CO₂ → Na₂CO₃ + H₂O. Formation of sodium carbonate changes the composition and lowers the purity of the stored hydroxide. Thus option A correctly explains both observations. The other options describe impossible transformations under ordinary open-air conditions.
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.
