Intermolecular Forces Question

[VCE_2012]

I need a sufficient answer for this:
"Butane and propan-1-ol have similar molar masses. The boiling point of butane is 138.4 C and that of propan-1-ol is 92.7 C. Explain in terms of intermolecular forces, the difference between the boiling points of these two compounds."

Its a 3 mark question.

Would I get 1 mark if only I commented that butane is a longer molecule hence the dispersion forces are stronger than that of propan-1-ol and more energy is required to disrupt the intermolecular forces.? : ?

[Aurelian]

I need a sufficient answer for this:
"Butane and propan-1-ol have similar molar masses. The boiling point of butane is 138.4 C and that of propan-1-ol is 92.7 C. Explain in terms of intermolecular forces, the difference between the boiling points of these two compounds."

Its a 3 mark question.

Would I get 1 mark if only I commented that butane is a longer molecule hence the dispersion forces are stronger than that of propan-1-ol and more energy is required to disrupt the intermolecular forces.? : ?

The boiling point of butane is actually around about 0 degrees celsius, so the information in the stem is misleading. Where'd this question come from...?

Either way, to net full marks, you'd need to discuss dispersion force strength being roughly equal for both as the molecules are of roughly the same size/electron count (as indicated in the question). That is, butane being 'longer' doesn't really have much of an influence (in fact, it's actually propan-1-ol which has the greater molar mass...).  You would hence then need to designate the discriminating factor as being the hydrogen bonding which can occur in propan-1-ol, which would account for its demonstrably higher boiling point.

[Lasercookie]

Unless you've taken it from some other source, the question appeared in VCAA 2010. However, the question stem there states negative 138.4 C for butane, which makes a lot more sense (I'm guessing they made it that much lower than 0 C to guide students directly to the right answer).

[VCE_2012]

Unless you've taken it from some other source, the question appeared in VCAA 2010. However, the question stem there states negative 138.4 C for butane, which makes a lot more sense (I'm guessing they made it that much lower than 0 C to guide students directly to the right answer).

(Image removed from quote.)

Whoops, I totally ignored the negative.