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

Analysis of the third alcohol homologue 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 first three homologues are:
1st Homologue: Methanol (CH$_3$OH)
2nd Homologue: Ethanol (C$_2$H$_5$OH)
3rd Homologue: Propanol (C$_3$H$_7$OH)
Molecular Mass Calculation for Propanol:
Carbon (C): 3 atoms $\times$ 12 g/mol/atom = 36 g/mol
Hydrogen (H): 8 atoms $\times$ 1 g/mol/atom = 8 g/mol
Oxygen (O): 1 atom $\times$ 16 g/mol/atom = 16 g/mol
Total Molecular Mass: 36 + 8 + 16 = 60 g/mol.
2. Boiling Point Trend:
In the alcohol series, progression from lower to higher molecular mass homologues results in:
Increased molecular size and mass.
Enhanced van der Waals forces and more significant hydrogen bonding between molecules.
Consequently, the boiling point rises as molecular mass increases.