Why can washing soda crystals gradually become powdery when left exposed to air?
Answer and explanation
Correct answer: They lose water of crystallisation
The governing concept is water of crystallisation in hydrated salts. Washing soda is sodium carbonate decahydrate, Na₂CO₃·10H₂O. When exposed to dry air, it can lose some or all of this bound water, a process called efflorescence. The crystal lattice changes and the crystals may become powdery or less transparent. This is not caused by absorbing oxygen, changing into nitrogen, or releasing hydrogen gas. Therefore option A is correct.
Frequently asked questions
What is the correct answer to this question?
They lose water of crystallisation
Why is this the correct answer?
The governing concept is water of crystallisation in hydrated salts. Washing soda is sodium carbonate decahydrate, Na₂CO₃·10H₂O. When exposed to dry air, it can lose some or all of this bound water, a process called efflorescence. The crystal lattice changes and the crystals may become powdery or less transparent. This is not caused by absorbing oxygen, changing into nitrogen, or releasing hydrogen gas. Therefore 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.
