Two liquids at different boiling points but both at atmospheric pressure.?

Question

You have two coloress molecular liquids, one boiling at -84C and other at 34 C both at atmospheric pressure.

Which of the following statement is correct? Correct those that are not.

1). The higher-boiling liquid has greater intermolecular forces than the other.

2) the lower boiling liquid must consist of nonpolar molecules.

3) the lower boiling liquid has lower molecular weight than the higher boiling liquid

4) the two liquids have identical vapor pressure at their normal boiling points

Answer 1

The answer is 1. Intermolecular is the force between different molecules. Intra is the force within a molecule.

If the intermolecular forces for one substance are greater than those of another, that material will have a higher BP.

Answer 2

Best answer is #3 - molecular weight does correlate with BP, which is why the BP of water is such a surprising exception.

#1 intermolecular forces are inside the molecule. But vaporization (evaporating) does not typically change the molecule.

#2 really there is nothing in the description about polarity. There are some very small polar compounds with low BP, there are some very large non-polar compounds with high BP.

#4 if the two liquids had identical vapor pressure, they’d have similar boiling points. There may be some exotic systems where this is not the case, but it is a good generalization.

Answer 3

Boiling point is defined as the temperature at which the vapour pressure is the same as atmospheric pressure, ie the same.