What is the difference between the molecular masses of two successive members of the homologous series?

The correct answer is 14 u.

Key Points:

• homologous series
  • A homologous series is made up of substances with the same functional group and similar chemical properties.
  • A homologous series' members are referred to as homologs.
  • A -CH₂ group distinguishes the following members of a homologous series from one another.
  • A -CH₂ group has a molecular mass of 14 amu.
  • As a result, the mass of each succeeding homologue in a homologous series varies by 14 amu. 

Additional Information:

• Methane (CH₄) is followed by ethane (C₂H₆), propane (C₃H₈), butane (C₄H₁₀), and pentane (C5H12) in the homologous series of straight-chained alkanes.
• In that series, each new methylene bridge (-CH₂- unit) introduced in the chain causes the subsequent members to differ in mass.
• As a result, each member's molecular mass varies by 14 atomic mass units.
• "Adjacent homologues" are members of such a series that are close to one another, such as methane and ethane.
• Numerous physical characteristics in that series, such as the boiling point, gradually alter with increasing mass.
• Ethane (C₂H₆), for instance, has a higher boiling point than methane (CH₄).