Question

A 0.535 g in mixture of ethanol and acetaldehyde when heated with Fehling's solution gave 1.2 g of a red precipitate. What is the percentage of acetaldehyde in the mixture?

• A. $34.4$
• B. $47.6$
• C. $68.8$
• D. $95.2$

Answer 1

The correct option is C $68.8$

Let there be x gm of $C{H}_{3}CHO$ and $(0.535-xgm)$ of $C_2{H}_{5}OH$.

(Only aldehyde reacts with Fehling's solution, not alcohol)

1 mol of $C{H}_{3}CHO$ (44 gm) = 1 mol of red ppt. of $C{u}_{2}O$ (143 gm).

143gm of precipitate is obtained from 44 gm of $C{H}_{3}CHO$.

1.2 gm of precipitate is obtained from:

$\frac{44}{143}\times 1.2\approx 0.348$ gm of $C{H}_{3}CHO$

Percent of $C{H}_{3}CHO=\frac{0.368}{0.535}\times 100\approx 68.8$ %