Question

Select the pair of substances in which the one with the lower boiling point is listed first. (SELECT ONE LETTER)

A) C₇H₁₆, C₅H₁₂

_B) CF₄, CBr₄

C) H₂O, H₂S

D) CH₃CH₂OH, CH₃–O–CH₃

_E) Xe, Kr

Answer 1

A)

C7H16 and C5H12 are both non polar.

The one with greater molar mass will have greater dispersion force between molecules and hence higher boiling point.

Molar mass is greater for C7H16.

So, C7H16 has higher boiling point.

B)

CF4 and CBr4 are both non polar.

The one with greater molar mass will have greater dispersion force between molecules and hence higher boiling point.

Molar mass is greater for CBr4.

So, CBr4 has higher boiling point.

This is correct

C)

H2O can form hydrogen bond but H2S Can’t.

So, H2O has higher boiling point.

D)

CH3CH2OH can form hydrogen bond but CH3-O-CH3 Can’t.

So, CH3CH2OH has higher boiling point.

E)

Xe and Kr are both non polar.

The one with greater molar mass will have greater dispersion force between molecules and hence higher boiling point.

Molar mass is greater for Xe.

So, Xe has higher boiling point.

Answer: B