You have four test tubes, A, B, C and D containing sodium carbonate, sodium chloride, lime water and blue litmus solutions respectively. Out of these the material of which test tube/ test tubes would be suitable for the correct test of acetic/ethanoic acid?
(a) only A
(b) A and B
(c) B and C
(d) A and D
Solution
Ethanoic (acetic) acid is an acid, and it will change blue litmus solution to red.
The chemical reaction between ethanoic (acetic) acid and sodium carbonate is:
2 CH3COOH + Na2CO3 → 2 CH3COONa + CO2 + H2O
On passing CO2 gas through lime water, the lime water turn milky. The milky apprearance of lime water is due to the formation of solid calcium carbonate (CaCO3).
Reaction:
Ca(OH)2 + CO2 → CaCO3 + H2O
Therefore, out of four test tubes A, B, C and D, only A and D test tubes would be suitable for the correct test of acetic/ethanoic acid.
Acetic acid also reacts with lime water to give calcium acetate (CH3COO)2Ca) as a product. But here it is not consider as correct test of acetic/ethanoic acid.
Reaction:
2 CH3COOH + Ca(OH)2 → (CH3COO)2Ca + 2 H2O
Hence, the correct answer is option (d).
