Question

What is the difference in molar mass of any two neighbouring alkanes?

• A. \(12 \, \text{g mol}^{-1}\)
• B. \(10 \, \text{g mol}^{-1}\)
• C. \(15 \, \text{g mol}^{-1}\)
• D. \(14 \, \text{g mol}^{-1}\)

Hint:

Members of a homologous series always differ by a \(\mathrm{CH_2}\) group, corresponding to a mass difference of \(14 \, \text{g mol}^{-1}\).

Answer 1

The Correct Option is D

Step 1: Recall the general formula of alkanes.
Alkanes follow the general molecular formula \(\mathrm{C_nH_{2n+2}}\). Each successive member of the homologous series differs by one \(\mathrm{CH_2}\) unit.
Step 2: Calculate the molar mass of the repeating unit.
The molar mass of one \(\mathrm{CH_2}\) unit is:
\[ 12 + (2 \times 1) = 14 \, \text{g mol}^{-1} \]
Step 3: Conclusion.
Hence, the difference in molar mass between any two neighbouring alkanes is \(14 \, \text{g mol}^{-1}\).