Question

Which compound (water, acetone, ethanol, hexane, decane, or 1-decanol) do you think will be the least volatile and explain why. You must discuss intermolecular forces in your explanation.

Answer 1

The volatility order for above compounds will be :

water > 1-decanol > ethanol > acetone > decane > hexane

1. Water and alcohol both are polar covalent molecules but still water is least volatile because water forms more strong hydrogen bonds in comparison to alcohols as water has two hydrogen atoms it can form two hydrogen bonds while ethanol can form only one hydrogen bond.

2.Comparing the two alcohols (1-decanol and ethanol) 1-decanol is less volatile than ethanol because as the molecular weight increases boiling point increases. remember, alcohols not only have hydrogen bonding but they also have van der waals dispersion forces.so as the chain length increases van der waals forces increases and boiling point increases.

3.Acetone is less volatile than non polar compounds (hydrocarbons).this is because acetone has polar carbonyl group and hence undergo weak intermolecular association due to dipole-dipole interactions between the opposite ends of the c=o dipoles. the dipole-dipole interactions are however weaker than intermolecular hydrogen bonding between alcohol molecules.

4.Hydrocarbons are highly volatile of all the compounds.because they have weak intermolecular forces called dispersion forces.as the no of carbon in the hydrocarbon increases,the strength of the intermolecular forces increases thus  boiling point also increases which is why decane is less volatile than hexane.