Chemistry
Assertion (A): A white powder forms on the surface of washing soda crystals which are left exposed to the air.
Reason (R): Washing soda is a hygroscopic substance.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Answer
A is true but R is false.
Explanation — Washing soda (hydrated sodium carbonate), when exposed to dry air, loses water of crystallization. The result is the formation of white anhydrous sodium carbonate (Na2CO3) on the surface, which appears as a white powder. Hence the assertion (A) is true. Washing soda undergoes efflorescence, meaning it loses moisture (its water of crystallization) to the air. So washing soda is efflorescent, not hygroscopic. Hence the reason (R) is false.
Related Questions
Assertion (A): Water is a universal solvent.
Reason (R): Water dissolves all substances except noble metals and glass.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Assertion (A): A saturated solution becomes unsaturated on heating.
Reason (R): More amount of solute can dissolve in a solvent upon heating.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Assertion (A): A crusty 'boiler scale' is formed in boilers when hard water is used.
Reason (R): Hard water contains bicarbonates of calcium and magnesium.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.
Assertion (A): Efflorescence is minimum during humid conditions.
Reason (R): Efflorescence occurs when the vapour pressure of the hydrated crystals exceeds the vapour pressure of the atmospheric humidity.
- Both A and R are true and R is the correct explanation of A.
- Both A and R are true but R is not the correct explanation of A.
- A is true but R is false.
- A is false but R is true.