Question

Write the formula and the molecular mass of the third homologue of alcohols. State how the boiling point of an alcohol changes as one moves from lower to higher homologues.

Answer 1

Let's analyze the third homologue of alcohols and its boiling point trend:
{1.Formula and Molecular Mass of the Third Homologue:}
The general formula for alcohols is C$_n$H$_{2n+1}$OH. The homologues are as follows:
1st Homologue: Methanol (CH$_3$OH)
2nd Homologue: Ethanol (C$_2$H$_5$OH)
3rd Homologue: Propanol (C$_3$H$_7$OH)
Molecular Mass:
Carbon (C): 3 $\times$ 12 = 36
Hydrogen (H): 8 $\times$ 1 = 8
Oxygen (O): 1 $\times$ 16 = 16
Total Molecular Mass: 36 + 8 + 16 = 60 g/mol.
{2.Boiling Point Trend:}
As we move from lower to higher homologues in alcohols:
The molecular size and molecular mass increase.
This leads to stronger van der Waals forces and more extensive hydrogen bonding between alcohol molecules.
Consequently, the boiling point increases with increasing molecular mass.