Question

What is the difference in molar masses of Undecane and Decane?

• A. 140 g mol$^{-1}$
• B. 70 g mol$^{-1}$
• C. 24 g mol$^{-1}$
• D. 14 g mol$^{-1}$

Hint:

Successive members of an alkane series differ by a methylenyl group ($-\text{CH}_2$), which weighs 14 units.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Alkanes form a homologous series where each successive member differs by a methylene (\(-\text{CH}_2-\)) group.
Step 2: Key Formula or Approach:
Successive member difference = 1 Carbon + 2 Hydrogens.
Step 3: Detailed Explanation:
1. Decane has 10 carbons: \(\text{C}_{10}\text{H}_{22}\).
2. Undecane has 11 carbons: \(\text{C}_{11}\text{H}_{24}\).
The formula difference is \(\text{CH}_2\).
Molar mass of \(\text{CH}_2 = 12 + (2 \times 1) = 14 \text{ g/mol}\).
Step 4: Final Answer:
The difference is 14 g mol$^{-1}$.