Question

An organic compound contains 69.77% C, 11.63% H and 18.6% O. Its molecular formula is same as its empirical formula. The number of carbon atoms present per molecule would be:

• A. 4
• B. 5
• C. 6
• D. 7

Hint:

Percent to Mass $\rightarrow$ Mass to Mole $\rightarrow$ Divide by Small $\rightarrow$ Multiply 'til Whole.

Answer 1

The Correct Option is B

Step 1: Concept
The empirical formula represents the simplest whole-number ratio of atoms in a compound.

Step 2: Meaning
Divide the percentage of each element by its atomic mass to find the molar ratio: C: $69.77/12 = 5.81$; H: $11.63/1 = 11.63$; O: $18.6/16 = 1.16$.

Step 3: Analysis
Divide by the smallest value (1.16) to get the ratio: C: $5.81/1.16 \approx 5$; H: $11.63/1.16 \approx 10$; O: $1.16/1.16 = 1$.

Step 4: Conclusion
The empirical formula is $C_5H_{10}O$. Since the molecular formula is the same, there are 5 carbon atoms per molecule. Final Answer: (B)