Determine the molecular formula of an alkane if its molecular weight is 170.

Solution:
1. Alkanes have the general formula: CnH2n + 2. Index n cannot be 0.
2. The relative atomic mass of carbon is 12, for hydrogen it is 1.
3. Since the molecular weight of the alkane is 170, the equation was drawn up:
12 * n + 1 * (2n + 2) = 170;
12n + 2n + 2 = 170;
12n + 2n = 170 – 2;
14n = 168;
n = 168/14;
n = 12;
If n = 12, then 2n + 2 = 2 * 12 + 2 = 26.
The alkane has the formula C12H26.
Answer: The molecular formula of the alkane is C12H26.