Question

Indicate the force that is the predominant reason that one material in each pair in the question above has a higher boiling point than the other. (This would be the force that is present in one material but not the other, or that is greater in one material than the other.) (either a. b or c)

1a) NH₃ or PH₃

(a)dipolar forces

(b)dispersion forces

(c)hydrogen bonding

1b) C₂H ₅OH or H₃C-O-CH₃

(a)dipolar forces

(b)dispersion forces   

(c)hydrogen bonding

1c) C₄H₈ or C₁₀H₂₀

(a)dipolar forces

(b)dispersion forces   

(c)hydrogen bonding

1d) H₂S or F₂

(a)dipolar forces

(b)dispersion forces   

(c)hydrogen bonding

Answer 1

1 (a) NH3 has higher boiling point than PH3

hydrogen bonding ...... answer

NH3 has very polar N-H bonds leading to strong hydrogen bonding. This the dominant intermolecular force and results in a greater attraction between NH3 molecules than there is between PH3 molecules.

1(b) C2H5OH has higher boiling point than CH3-O-CH3

hydrogen bonding ............ answer

in C2H5OH , the hydrogen and the oxygen are bonded, which results in a large electronegativity difference. This allows hydrogen bonding to occur.

in H3C-O-CH3,  the oxygen is bonded to a carbon and the electronegativity difference is small. Due to this, it forms only dipole dipole attractions rather than hydrogen bonds.

1(c) C10H20 has higher boiling point than C4H8

dispersion forces .................. answer

1 (d) H2S has higher noiling point than F2

  dipolar forces ............. answer

as H2S is polar and F2 is nonpolar