9701 MCQ Solution 4

Question 4: [Physical > Bonding]:

The African weaver ant defends its territory by spraying an intruder with a mixture of compounds. The ease by which these compounds are detected by other ants depends upon the volatility, which decreases as the strength of the intermolecular forces in the compound increases.

Which compound would be the most volatile?

A CH_3­CH₂CH₂CH₂CH₂CH₃

B CH_3­CH₂CH₂CH₂CH₂CHO

C CH_3­CH₂CH₂CH₂CH₂NH₂

D CH_3­CH₂CH₂CH₂CH₂OH

Reference: Past Exam Paper – November 2002 Paper 1 Q4

Solution 4:

Answer: A.

The compound in answer A is a long chain hydrocarbon and the only noticeable intermolecular forces are Van der Waals forces. The compound in B has a C=O bond present which, though slight due to the large size of the molecule, can cause a permanent dipole – dipole attraction to be setup. Thus the compound in B is less volatile than the compound in A. Both compounds in C and D have a hydrogen atom bonded to a nitrogen and oxygen atom, respectively. This allows for the formation of hydrogen bonds between molecules of the compound due to the difference in electro negativities between hydrogen and the other atom. Hydrogen bonds are the strongest intermolecular force thus both these options are eliminated. Hence correct answer is A.