Question

Two separate solutions, Fehling's solution A ($CuS{O}_4$) and Fehling's solution B($NaOH$ + Rochelle salt) are at first mixed up together and is then heated with the aldehyde. The precipitate formed is:

• A. $\left[Cu\right(H_{2}O{)}_4\left(OH{)}_2\right]$
• B. $CuC{O}_3$
• C. $C{u}_{2}O$
• D. $Cu$

Answer 1

The correct option is C $C{u}_{2}O$

Two separate solutions, Fehling's solution A ($CuS{O}_4$) and Fehling's solution B($NaOH$ + Rochelle salt) are at first mixed up together and is then heated with the aldehyde. A $C{u}_{2}O$ precipitate is formed.
$RCHO+2C{u}^{2+}+5O{H}^{-}\stackrel{\Delta }{\to }RCO{O}^{-}+C{u}_{2}O\downarrow +3H_{2}O$
Fehling solution is the tartaric acid complex of cupric ions.
The aldehyde is oxidized to carboxylate ion and the cupric ion is reduced to cuprous oxide.