Question

What is the source of an alkane if its molar mass is 100 and the percentage by mass of hydrogen is 16?

• A. Waxes
• B. Diesel
• C. LPG
• D. Petrol

Hint:

Alkanes with carbon number from C\(_5\) to C\(_9\) mainly occur in petrol.

Answer 1

The Correct Option is D

Step 1: Use the general formula of alkanes.
Alkanes have the general formula \( \mathrm{C_nH_{2n+2}} \).
Step 2: Express molar mass in terms of \(n\).
Molar mass \(= 12n + (2n+2) = 14n + 2 \).
Given molar mass \(= 100\).
\[ 14n + 2 = 100 \]
\[ 14n = 98 \Rightarrow n = 7 \]
Step 3: Identify the alkane.
For \(n = 7\), the alkane is heptane \(\mathrm{C_7H_{16}}\).
Step 4: Match with petroleum fractions.
Heptane is a major constituent of petrol (gasoline).
Step 5: Conclusion.
The given alkane belongs to the petrol fraction.