The boiling points for a set of compounds in a homologous series can be qualitatively predicted using intermolecular force strengths. Using their condensed structural formulas, rank the homologous series for a set of alkanes by their boiling point.

Rank from highest to lowest boiling point. To rank items as equivalent, overlap them.
a)CH3CH2CH2CH3 b) CH3CH2CH2CH2CH2CH3
CH3
c) CH3CH2CCH2CH3
CH3

d)CH3CH2CH2CH2CH2CH2CH3
answer is D, B , C, A

The boiling point of another member of this homologous series was found to be 309 K. What is the likely molecular formula for this compound??????
Express your answer as a chemical formula.

The boiling points for the "straight chain" isomers and isoalkanes isomers are shown to demonstrate that branching decreases the surfaces area and lowers the boiling point (this because intermolecular force strengths weakens).

a) CH3CH2CH2CH3 = C4H10 = Butane

b) CH3CH2CH2CH2CH2CH3 CH3 = C7H17

c) CH3CH2CCH2CH3 CH3 = C6H13 = Hexyl radical

d) CH3CH2CH2CH2CH2CH2CH3 = C7H16 = Heptane

Heptane and the C7H17 has a higher boiling point than butane and then the hexyl radical since those have more C atoms.

Butane has the lowest boiling point

Heptane has the highest boiling point

Boiling point of D > B > C > A

C7H17 has a lower boiling point than heptane because branching decreases the boiling point.

Members of this homologous series are all of the form CnH(2n+2). Since the boiling point of hexane is given to be 342 K, and the boiling point of butane is 273 K, we know that n must equal a whole number between 6 and 4.

Therefore, it must equal 5. C5H2*5+2 = C5H12 = Pentane

Pentane has a boiling boint of 309 Kelvin.