Question

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

• A. 10 g mol
• B. 14 gm mol-
• C. 12 g mol¹
• D. 15 g mol-

Answer 1

Answer: (B)

14 gm mol-

Answer 2

For alkanes, the general formula is

$$\mathrm{C}_n\mathrm{H}_{2n+2}$$

For two consecutive alkanes, say $\mathrm{C}_n\mathrm{H}_{2n+2}$ and $\mathrm{C}_{n+1}\mathrm{H}_{2(n+1)+2}$, the difference is one extra $\mathrm{CH}_2$ group. Hence, the difference in molar mass is:

$$\text{Molar mass of } \mathrm{CH}_2 = 12 + 2 = 14\, \text{g/mol}$$