Chemistry Miscellaneous · Laboratory apparatus and chemical tests
Q1. When carbon dioxide is passed through lime water, which colour precipitate is obtained?
- (a) Red
- (b) Green
- (c) Blue
- (d) White
Answer & solution
Answer: (d) White
Correct Answer: White (Option 4)
When CO₂ is passed through lime water [Ca(OH)₂], a white precipitate of calcium carbonate ( CaCO ₃) is formed:
CO₂ + Ca(OH)₂ → CaCO ₃↓ (white) + H₂O
This is the standard test for CO₂ — it turns lime water milky white.
Why other options are wrong:
Option 1 – Red precipitate is not formed in this reaction.
Option 2 – Green precipitate is not formed.
Option 3 – Blue precipitate is not formed. CaCO ₃ is characteristically white.
When CO₂ is passed through lime water [Ca(OH)₂], a white precipitate of calcium carbonate ( CaCO ₃) is formed:
CO₂ + Ca(OH)₂ → CaCO ₃↓ (white) + H₂O
This is the standard test for CO₂ — it turns lime water milky white.
Why other options are wrong:
Option 1 – Red precipitate is not formed in this reaction.
Option 2 – Green precipitate is not formed.
Option 3 – Blue precipitate is not formed. CaCO ₃ is characteristically white.