Calculate the mass percentage of Aspirin (${\mathrm{C}}_9{\mathrm{H}}_8{\mathrm{O}}_4$) in Acetonitrile (${\mathrm{CH}}_3\mathrm{CN}$) when$6.5\mathrm{g}$ of ${\mathrm{C}}_9{\mathrm{H}}_8{\mathrm{O}}_4$ is dissolved in $450\mathrm{g}$of ${\mathrm{CH}}_3\mathrm{CN}$.

Step 1: Given data

Molecular mass of Aspirin (${\mathrm{C}}_9{\mathrm{H}}_8{\mathrm{O}}_4$): $(9\times 12+8\times 1+4\times 16)=180\mathrm{g}$

Molecular mass of Acetonitrile (${\mathrm{CH}}_3\mathrm{CN}$): $(12+3\times 1\hspace{0.17em}+12+14)=41\mathrm{g}$

Given mass of Aspirin (${\mathrm{C}}_9{\mathrm{H}}_8{\mathrm{O}}_4$) : $6.5\mathrm{g}$

Given mass of solvent Acetonitrile (${\mathrm{CH}}_3\mathrm{CN}$): $450\mathrm{g}$

Formula for mass percentage: $\frac{\mathrm{Mass}\mathrm{of}\mathrm{solute}}{\mathrm{Mass}\mathrm{of}\mathrm{solute}+\mathrm{Mass}\mathrm{of}\mathrm{solvent}}$

Step 2: Determination of mass percentage of Aspirin
The mass percentage of Aspirin ( ${\mathrm{C}}_9{\mathrm{H}}_8{\mathrm{O}}_4$) = $\frac{\mathrm{Mass}\mathrm{of}\mathrm{aspirin}\left(\mathrm{solute}\right)}{\mathrm{Mass}\mathrm{of}\mathrm{aspirin}\left(\mathrm{solute}\right)+\mathrm{mass}\mathrm{of}\mathrm{acetonitrile}\left(\mathrm{solvent}\right)}$

Step 3: Calculation of mass percentage of Aspirin
So, Mass percentage of Aspirin ( ${\mathrm{C}}_9{\mathrm{H}}_8{\mathrm{O}}_4$) =$\frac{6.5}{6.5+450}\times 100$

= $0.0142\times 100$
which means the mass percentage of Aspirin ( ${\mathrm{C}}_9{\mathrm{H}}_8{\mathrm{O}}_4$) = 1.42%

Hence, the mass percentage of Aspirin is 1.42%