Question

what is the percent composition of aspirin, c₉h₈o₄? (molar mass of c₉h₈o₄ = 180.16 g/mol)
50.00 % c, 9.48 % h, 40.52 % o
60.00 % c, 4.48 % h, 35.52 % o
40.00 % c, 4.48 % h, 55.52 % o
30.00 % c, 4.48 % h, 65.52 % o
60.00 % c, 9.48 % h, 30.52 % o

Explanation:

Step1: Calculate mass of carbon

The atomic mass of C is approximately 12.01 g/mol. In $C_9H_8O_4$, there are 9 C atoms. So mass of C in 1 - mole of $C_9H_8O_4$ is $9\times12.01 = 108.09$ g. Percent of C = $\frac{108.09}{180.16}\times100\%\approx60.00\%$.

Step2: Calculate mass of hydrogen

The atomic mass of H is approximately 1.01 g/mol. In $C_9H_8O_4$, there are 8 H atoms. So mass of H in 1 - mole of $C_9H_8O_4$ is $8\times1.01 = 8.08$ g. Percent of H = $\frac{8.08}{180.16}\times100\%\approx4.48\%$.

Step3: Calculate mass of oxygen

The atomic mass of O is approximately 16.00 g/mol. In $C_9H_8O_4$, there are 4 O atoms. So mass of O in 1 - mole of $C_9H_8O_4$ is $4\times16.00 = 64.00$ g. Percent of O = $\frac{64.00}{180.16}\times100\%\approx35.52\%$.

Answer:

60.00 % C, 4.48 % H, 35.52 % O (corresponds to the second option in the multiple - choice list)