What is the percent composition by mass of carbon in a sample of propanol, CH3CH2CH2OH? The molar mass of propanol is 60.09 g∙mol–1.单项选择题
A
20.0% carbon
B
25.0% carbon
C
51.0% carbon
D
60.0% carbon

Question

What is the percent composition by mass of carbon in a sample of propanol, CH3CH2CH2OH?  The molar mass of propanol is 60.09 g∙mol–1.

BlackTom AI · Accepted Answer

To determine the percent composition by mass of carbon in propanol, we first identify the molecular formula and its molar mass.
Propanel (propanol) has the formula C3H8O, which means it contains 3 carbon atoms.
The approximate atomic masses are: C ≈ 12.01 g/mol, H ≈ 1.008 g/mol, O ≈ 16.00 g/mol. Therefore the molar mass of C3H8O is about (3×12.01) + (8×1.008) + (1×16.00) = 36.03 + 8.064 + 16.00 ≈ 60.09 g/mol, which matches the given molar mass of 60.09 g/mol.
Next, calculate the mass contributed by carbon: 3 carbons × 12.01 g/mol ≈ 36.03 g of carbon per mole of propanol.
Now compute the mass percent of carbon: (mass of carbon / molar mass of propanol) × 100 = (36.03 / 60.09) × 100 ≈ 0.600 × 100 ≈ 60.0%.

Option-by-option analysis:
- 20.0% carbon: This would imply only about one-sixth of the propanol’s mass is carbon, which contradicts the actual carbon mass of 36.03 g out of 60.09 g. The calculation shows a much higher fraction of carbon than 20%.
- 25.0% carbon: Similar issue as above; a quarter of the mass being carbon does not align with the calculated 60.0% from the C3H8O composition.
- 51.0% carbon: This is closer to the 60% value but still underestimates the carbon contribution derived from three carbons out of the total molecular mass; the exact ratio is about 60.0%, not 51.0%.
- 60.0% carbon: This matches the calculated value precisely since 36.03 g of carbon per 60.09 g of propanol yields about 60.0% carbon by mass.

In summary, the correct approach uses the molecular formula to find the carbon mass (3×12.01 g) and divides by the molar mass of propanol, giving approximately 60.0% carbon. The other options represent miscalculations or mismatches with the actual carbon fraction in C3H8O.

What is the percent composition by mass of carbon in a sample of propanol, CH3CH2CH2OH? The molar mass of propanol is 60.09 g∙mol–1.单项选择题

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