0.5 gm mixture of ethanal and acetone heated with Fehling solution gave 0.975 gm. of red precipitate. If x is the percentage of acetone in the mixture, find $\frac{x}{10}$ ? (Atomic mass of Cu = 63.5)

Percentage of Acetone in Mixture from Fehling Test

A mixture of ethanal and acetone weighing 0.5 g is heated with Fehling solution, producing 0.975 g of red precipitate (Cu₂O).

The atomic mass of Cu = 63.5.

Key Points:

• Acetone does not react with Fehling's solution.
• Ethanal reacts with Fehling's, producing Cu₂O precipitate.
• Molar mass of ethanal (CH₃CHO) = 44 g/mol.
• Molar mass of Cu₂O = (2×63.5 + 16) = 143 g/mol.

Calculation:

2 CH₃CHO + 4 Cu²⁺ + 8 OH⁻ → 2 CH₃COO⁻ + 4 Cu₂O (red) + 4 H₂O

From stoichiometry, 2 moles of ethanal produce 4 moles of Cu₂O.

Let x be the percentage of acetone in the mixture.

Using molar masses and precipitate mass, solving the equation gives:

x ≈ 70%

Therefore, x/10 = 7.0.