Learners investigate factors which influence the boiling points of alcohols - NSC Physical Sciences - Question 3 - 2017 - Paper 2

Alcohols are flammable, which means they can easily catch fire. Heating them in a water bath provides a controlled and safer method of heating without exposing them directly to a flame.

The alcohols must be primary alcohols and have similar chain lengths and molecular structures to ensure fair comparison of their boiling points. Using straight-chain primary alcohols offers consistency in structural properties.

The boiling points of the alcohols increase with chain length. This trend can be attributed to the increasing strength of intermolecular forces, such as London dispersion forces, as the molecular size increases. For instance, hexan-1-ol has a higher boiling point than pentan-1-ol because it has more carbon atoms, leading to stronger intermolecular attractions that require more energy to overcome.

Remains the same. Doubling the volume does not affect the boiling point of hexan-1-ol; the boiling point is a property of the substance itself, not the amount.

The independent variable for this comparison is the type of alcohol being tested, specifically comparing hexan-1-ol and hexanal.

Hexan-1-ol has a higher boiling point than hexanal due to the differences in their intermolecular forces. Hexan-1-ol contains an alcohol functional group which allows for hydrogen bonding, a stronger intermolecular force compared to the dipole-dipole forces present in hexanal. This greater energy requirement to break the hydrogen bonds in hexan-1-ol results in a higher boiling point.