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Question

A student has planned to prepare acetanilide from aniline using acetic anhydride.
The student has started from $9.3 \text{ g}$ of aniline. However, the student has managed to obtain $11 \text{ g}$ of dry acetanilide.
The % yield of this reaction is :-

The correct answer is
81.50%

Calculating Acetanilide Percent Yield

This solution explains the calculation for the percent yield of acetanilide prepared from aniline and acetic anhydride, using the provided experimental masses.

Reaction Stoichiometry

The synthesis of acetanilide from aniline and acetic anhydride follows this reaction:

$ \text{C}_6\text{H}_5\text{NH}_2 + (\text{CH}_3\text{CO})_2\text{O} \rightarrow \text{C}_6\text{H}_5\text{NHCOCH}_3 + \text{CH}_3\text{COOH} $

The molar ratio between aniline ($\text{C}_6\text{H}_5\text{NH}_2$) and acetanilide ($\text{C}_6\text{H}_5\text{NHCOCH}_3$) is 1:1.

Step 1: Calculate Moles of Aniline

Approximate molar mass of aniline ($\text{C}_6\text{H}_5\text{NH}_2$) is $93 \text{ g/mol}$.

Given mass of aniline = $9.3 \text{ g}$.

$ \text{Moles of Aniline} = \frac{9.3 \text{ g}}{93 \text{ g/mol}} = 0.1 \text{ mol} $

Step 2: Determine Theoretical Yield of Acetanilide

Approximate molar mass of acetanilide ($\text{C}_6\text{H}_5\text{NHCOCH}_3$) is $135 \text{ g/mol}$.

From the 1:1 stoichiometry, 0.1 mol of aniline theoretically yields 0.1 mol of acetanilide.

$ \text{Theoretical Yield} = \text{Moles} \times \text{Molar Mass} $

$ \text{Theoretical Yield} = 0.1 \text{ mol} \times 135 \text{ g/mol} = 13.5 \text{ g} $

Step 3: Calculate Percent Yield

The actual yield of acetanilide obtained is $11 \text{ g}$.

The formula for percent yield is:

$ \text{% Yield} = \left( \frac{\text{Actual Yield}}{\text{Theoretical Yield}} \right) \times 100\% $

Substitute the values:

$ \text{% Yield} = \left( \frac{11 \text{ g}}{13.5 \text{ g}} \right) \times 100\% $

$ \text{% Yield} \approx 0.8148 \times 100\% \approx 81.48\% $

Rounding to one decimal place, the percent yield is $81.5\%$.

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