JEE Main 2023 · 10 April · evening · Single correct · +4 / −1
Number of water molecules in washing soda and soda ash respectively are :
- (a) 1 and 0
- (b) 10 and 1
- (c) 1 and 10
- (d) 10 and 0
Answer and solution
Answer (d) 10 and 0
Solution
Chemistry ma’am · 4 steps
Same sodium carbonate in both: washing soda carries ten waters, soda ash has had all of them driven off.
- Washing soda. Washing soda is the decahydrate Na₂CO₃.10H₂O. Each formula unit holds 10 water molecules of crystallisation.
- Soda ash. Soda ash is anhydrous sodium carbonate, Na₂CO₃. It contains 0 water molecules.
- How they connect. Heating washing soda first gives the monohydrate. Above about 373 K the last water is lost too, and the white powder left behind is soda ash.
Na₂CO₃.10H₂O →(heat) Na₂CO₃.H₂O →(> 373 K) Na₂CO₃
- So. The counts are 10 and 0, which is option (d).
The idea to keep. Washing soda is Na₂CO₃.10H₂O, crystal carbonate is the monohydrate Na₂CO₃.H₂O, and soda ash is plain Na₂CO₃. Ash means everything wet has been burnt off.
Answer from the NTA final answer key. Solution by PrepWiser.