Question

Mass % of carbon in ethanol is

• A. 52
• B. 13
• C. 34
• D. 90
• E. 80

Hint:

In organic compounds, Oxygen usually lowers the carbon percentage. For example, in ethane (\(C_2H_6\)), Carbon is \(\approx 80\%\), but adding an Oxygen (ethanol) drops it to \(\approx 52\%\).

Answer 1

The Correct Option is A

Concept: Mass percentage is calculated using the formula: \[ \text{Mass \% of element} = \frac{\text{Mass of element in 1 mole of compound}}{\text{Molar mass of compound}} \times 100 \]

Step 1: Determine the molar mass of ethanol (\(C_2H_5OH\)).

• Carbon (C): \(2 \times 12.01 = 24.02 \, \text{g}\)
• Hydrogen (H): \(6 \times 1.008 = 6.048 \, \text{g}\)
• Oxygen (O): \(1 \times 16.00 = 16.00 \, \text{g}\) Total Molar Mass \(\approx 24 + 6 + 16 = 46 \, \text{g/mol}\).

Step 2: Calculate the percentage of Carbon.
\[ \text{Mass \% of C} = \frac{24}{46} \times 100 \] \[ \text{Mass \% of C} \approx 0.5217 \times 100 = 52.17\% \]