Question

Choose the substance with the lowest surface tension.

A. CH3CH2CH2CH3

B. CH3CH2CH2CH2CH2CH3

C. CH3NH2

D. CH3SH

E. CH3CH(CH3)CH3

I know that the answer is E but can someone please explain the difference the parathesis has on the surface tension? Because I was debating between A and E and they both have the same molar mass.

Thanks!

Answer 1

Surface tension is the net inward force experienced by the surface molecules. Higher the intermolecular interaction between molecules higher will be the surface tension.

CH3SH and CH3NH2 both are polar thus have strong interactions between them whereas other are non polar thus have weak dispersion force.

CH3CH2CH2CH2CH2CH3 has more atoms than other nonpolar compounds thus have strong dispersion force than other.

Out of CH3CH2CH2CH3 and CH3CH(CH3)CH3, first compound has high surface area because it has linear structure thus have strong dispersion force whereas in second compound, one CH3 group (in paranthesis) is present as branch on CH thus have less surface area and low dispersion force. Hence, E. has low surface tension.

Structure of A and E are :