Question

question 18 (1 point)
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when comparing boiling points of alkanes versus alcohols in the imf lab, you made a graph of boiling point versus molar mass. if comparing an alcohol with an alkane with the same number of carbons, like butanol and butane, which of the following is true?
the alkanes have the greater boiling points than alcohols.
the alkane has the stronger intermolecular forces.
the alkanes have greater molar masses than alcohols.
the alkane and the alcohol would have the same change in boiling point with increasing molar mass
the alkane has the greater change in boiling point (steeper slope) with increasing molar mass.

Explanation:

Alcohols have hydroxyl groups (\(-OH\)) which can form hydrogen bonds (a strong type of intermolecular force). Alkanes only have London dispersion forces (a relatively weak type of intermolecular force). When comparing an alcohol and an alkane with the same number of carbons (similar molar mass), the alcohol will have stronger intermolecular forces. The boiling point of a substance is related to the strength of its intermolecular forces (stronger forces mean higher boiling points). The slope of the boiling - point vs molar - mass graph is related to how much the boiling point changes with an increase in molar mass. Since alkanes have weaker intermolecular forces, a small increase in molar mass (which increases London dispersion forces) will lead to a relatively larger increase in boiling point compared to alcohols (because most of the intermolecular force “work” in alcohols is already done by hydrogen bonding, and additional molar - mass - induced London dispersion forces have a relatively smaller effect on boiling point).

Answer:

The alkane has the greater change in boiling point (steeper slope) with increasing molar mass.