Answer
3.33 g of acetic anhydride.
Work Step by Step
1. Calculate the number of moles of $C_7H_6O_3$:
Molar mass: 12.01* 7 + 1.008* 6 + 16.00* 3 = 138.12g/mol
$4.50g \times \frac{1 mol}{ 138.12g} = 0.0326mol (C_7H_6O_3)$
Since the given equation is already balanced:
The ratio of $C_7H_6O_3$ to $C_4H_6O_3$ is 1 to 1:
$0.0326 mol (C_7H_6O_3) \times \frac{ 1 mol(C_4H_6O_3)}{ 1 mol (C_7H_6O_3)} = 0.0326mol (C_4H_6O_3)$
2. Calculate the mass of $C_4H_6O_3$:
Molar mass: 12.01* 4 + 1.008* 6 + 16.00* 3 = 102.09g/mol
$0.0326 mol \times \frac{ 102.09 g}{ 1 mol} = 3.33g (C_4H_6O_3)$
