Question

What is the mass percent of oxygen in ethanol?

• A. $52.14\%$
• B. $13.13\%$
• C. $16\%$
• D. $34.73\%$

Answer 1

The correct option is D

$34.73\%$

Explanation for correct option:

$\mathbf{\left(}\mathbf{D}\mathbf{\right)}\mathbf{}\mathbf{34}\mathbf{.}\mathbf{73}\mathbf{\%}$

Step 1: Mass per cent formula:

• It is calculated as the mass of a component divided by the total mass of the percent compound, multiplied by $100$.

$\mathrm{Mass}\mathrm{\%}=\frac{\text{Mass of component}}{\text{Mass of compound}}\times 100$

Step 2: Determine molecular mass of ethanol

• The molecular formula of ethanol is ${\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}$.
• The molecular mass of ethanol is as follows:

$$\begin{gathered} \mathrm{Molecular}\mathrm{mass}\mathrm{of}{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}=(2\times \mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{C})+(6\times \mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{H})+\mathrm{Atomic}\mathrm{mass}\mathrm{of}\mathrm{O} \\ \mathrm{Molecular}\mathrm{mass}\mathrm{of}{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}=(2\times 12.01)+(6\times 1.008)+16 \\ \mathrm{Molecular}\mathrm{mass}\mathrm{of}{\mathrm{C}}_2{\mathrm{H}}_5\mathrm{OH}=46.07\mathrm{g} \end{gathered}$$

• $\mathrm{Molecular}\mathrm{mass}\mathrm{of}\mathrm{oxygen}\left({\mathrm{O}}_2\right)=16\mathrm{g}$

Step 3: To determine the mass percent of oxygen in ethanol.

$$\begin{gathered} \mathrm{Mass}\mathrm{\%}=\frac{\text{Mass of oxygen}}{\text{Mass of ethanol}}\times 100 \\ \mathrm{Mass}\mathrm{\%}=\frac{16\mathrm{g}}{46.07\mathrm{g}}\times 100 \\ \mathrm{Mass}\mathrm{\%}=34.73\mathrm{\%} \end{gathered}$$

Explanation for incorrect options

• The mass percentage of Oxygen is $34.73\%$.
• Hence , all the other options (A), (B) and (C) are incorrect.

Therefore, the correct option is$\mathbf{}\mathbf{\left(}\mathbf{D}\mathbf{\right)}\mathbf{}\mathbf{34}\mathbf{.}\mathbf{73}\mathbf{\%}$.