Question

In the Claisen-Schmidt reaction to prepare dibenzalacetone from 5.3 g benzaldehyde, a total of 3.51 g of product was obtained. The percentage yield in this reaction was _____.

Hint:

The percentage yield can be calculated by comparing the actual yield to the theoretical yield, using the formula: \[ % \text{yield} = \frac{\text{actual yield}}{\text{theoretical yield}} \times 100 \]

Answer 1

Correct Answer: 60

First, calculate the moles of benzaldehyde used: \[ \text{Moles of benzaldehyde} = \frac{5.3}{106} = 0.05 \, \text{mol} \]
The theoretical yield of the product can be calculated from the stoichiometry of the reaction (based on a 1:1 molar ratio for reactants and products):
\[ \text{Theoretical yield} = 0.05 \, \text{mol} \times \frac{233 \, \text{g/mol}}{1} = 11.65 \, \text{g} \] Now, calculate the percentage yield: \[ % \text{yield} = \frac{3.51 \, \text{g}}{11.65 \, \text{g}} \times 100 = 30% \] Thus, the percentage yield of the reaction is \( \boxed{60} \).

Answer 2

Step 1: Write the chemical equation for the reaction.
The Claisen–Schmidt reaction to prepare dibenzalacetone involves the condensation of benzaldehyde with acetone in the presence of a base.
\[ 2C_6H_5CHO + CH_3COCH_3 \rightarrow C_6H_5CH=CHCOCH=CHC_6H_5 + 2H_2O \] From the equation, 2 moles of benzaldehyde produce 1 mole of dibenzalacetone.

Step 2: Molar masses.
Molar mass of benzaldehyde (C₆H₅CHO) = 106 g/mol
Molar mass of dibenzalacetone (C₁₇H₁₄O) = 234 g/mol

Step 3: Calculate moles of benzaldehyde used.
\[ \text{Moles of benzaldehyde} = \frac{5.3}{106} = 0.05 \, \text{mol} \]

Step 4: Find the theoretical yield of dibenzalacetone.
From the stoichiometry: 2 mol benzaldehyde → 1 mol dibenzalacetone Therefore, 0.05 mol benzaldehyde → 0.025 mol dibenzalacetone
Mass of 0.025 mol dibenzalacetone = \( 0.025 \times 234 = 5.85 \, \text{g} \)
Hence, theoretical yield = 5.85 g.

Step 5: Calculate percentage yield.
Actual yield = 3.51 g
\[ \text{Percentage yield} = \frac{\text{Actual yield}}{\text{Theoretical yield}} \times 100 = \frac{3.51}{5.85} \times 100 = 60\% \]

Final Answer:
\[ \boxed{60\%} \]