8 mL of benzaldehyde reacted with acetone to produce dibenzalacetone. What is the theoretical yield in grams? Answer should be rounded to one decimal place. Molar weight: benzaldehyde = 106.23 g/mol, dibenzalacetone = 234.30 g/mol.
The Correct Answer and Explanation is:
Step 1: Balanced Chemical Equation
The aldol condensation between benzaldehyde and acetone proceeds as:2 C6H5CHO+CH3COCH3→C6H5CH=CHCOCH=CHC6H5+H2O2 \, \text{C}_6\text{H}_5\text{CHO} + \text{CH}_3\text{COCH}_3 \rightarrow \text{C}_6\text{H}_5\text{CH}=\text{CHCOCH}=\text{CHC}_6\text{H}_5 + \text{H}_2\text{O}2C6H5CHO+CH3COCH3→C6H5CH=CHCOCH=CHC6H5+H2O
This means 2 moles of benzaldehyde react with 1 mole of acetone to form 1 mole of dibenzalacetone.
Step 2: Convert Volume of Benzaldehyde to Moles
We are given:
- Volume of benzaldehyde = 8.0 mL
- Density of benzaldehyde = 1.044 g/mL (standard value)
- Molar mass of benzaldehyde = 106.23 g/mol
Mass of benzaldehyde=8.0 mL×1.044 g/mL=8.352 g\text{Mass of benzaldehyde} = 8.0 \, \text{mL} \times 1.044 \, \text{g/mL} = 8.352 \, \text{g}Mass of benzaldehyde=8.0mL×1.044g/mL=8.352gMoles of benzaldehyde=8.352 g106.23 g/mol≈0.0786 mol\text{Moles of benzaldehyde} = \frac{8.352 \, \text{g}}{106.23 \, \text{g/mol}} \approx 0.0786 \, \text{mol}Moles of benzaldehyde=106.23g/mol8.352g≈0.0786mol
Step 3: Use Stoichiometry to Find Moles of Product
From the balanced equation:
- 2 mol benzaldehyde → 1 mol dibenzalacetone
So:Moles of dibenzalacetone=0.07862=0.0393 mol\text{Moles of dibenzalacetone} = \frac{0.0786}{2} = 0.0393 \, \text{mol}Moles of dibenzalacetone=20.0786=0.0393mol
Step 4: Convert Moles to Grams
Mass=0.0393 mol×234.30 g/mol≈9.2 g\text{Mass} = 0.0393 \, \text{mol} \times 234.30 \, \text{g/mol} \approx 9.2 \, \text{g}Mass=0.0393mol×234.30g/mol≈9.2g
✅ Final Answer: 9.2 g
Conclusion (Textbook-style Summary)
To calculate the theoretical yield of dibenzalacetone, we first determine the number of moles of benzaldehyde used by converting the given volume to mass using its density and then to moles using its molar mass. From the balanced chemical reaction, two moles of benzaldehyde are needed to produce one mole of dibenzalacetone. We apply stoichiometry to find the expected moles of product and finally convert it to grams using the molar mass of dibenzalacetone. The theoretical yield is therefore 9.2 grams, assuming benzaldehyde is the limiting reagent and the reaction proceeds with 100% efficiency.
