Question

4. (a) Considering the general molecular formula for Alcohols (R-OH), what can you tell about the physical properties of Alcohols? (i.e. boiling point, miscibility in water...) (b) Compare the boiling points of 1-butene, propanal and 1-propanol explaining the reasoning behind it. (10 marks)

Answer 1

a) Alcohols have high boiling points compared to hydrocarbons, they are hydrophilic in nature and are miscible or soluble in water.

b) The boiling point of 1- propanol is 97 degrees centigrade , where as the boiling points of propionaldehyde and 1-butene are 49 and -6.3 degrees centigrade respectively.The large diffrence in boiling points indicates that alcohol molecules like ethanol and methanol are attracted to one another much stronger than hydrocarbons. Also this large difference in boiling point is due to the ability of alcohol molecules to form intermolecular hydrogen bonding.

Water and alcohols have similar properties. The water molecule has hydroxyl group and form hydrogen bond with another water molecule, similarly the alcohols have hydroxyl group which can be hydrogen bonded to water or other molecules. Because of this reason alcohols are soluble in water. Alcolhols with higher molecular weights tend to be less soluble in water and the hydrophobic nature increases with the increase in molecular weight.