5. Circle the intermolecular force that accounts for the following observations:

Question

5. Circle the intermolecular force that accounts for the following observations: (6) a. The boiling point of ammonia (NHo) is-33'C but the boiling point of phosphine (PHa) is-88 C Answer: hydrogen bonding dipole-dipole forces dispersion forces b. The boiling point of hydrogen (H) is-253°C but the boiling point of oxygen (O) is-183 Answer: hydrogen bonding dipole-dipole forces dispersion forces C. The boiling point of 1-carbon tetrachloride is 77°C but the boiling point of methane is-162 Answer: hydrogen bonding dipole-dipole forces dispersion forces CI CI CC HC-H carbon tetrachloride methane

Explanation / Answer

6]

a] Hydrogen bonding (NItrogen can form hydrogen bonds)

b] Dispersion forces (More the molecular weight more the dispersion forces and more the boiling point ]

c] Dispersion forces (More the molecular weight more the dispersion forces and more the boiling point ]

d] HYdrogen bonding

Acetic acid is a carboxylic acid for which hydrogen bonding would operate strongly. The acidic hydrogen would tend to interact with the electronegative oxygen on a NEIGHBOURING molecule; this force between molecules, this intermolecular force, tends to increase the boiling point. Such hydrogen bonding also operates in the very small water molecule, whose boiling point is even higher than the organic compounds.

On the other hand, in methyl formate, hydrogen is not bound to a strongly electronegative element. The molecule has no capacity to hydrogen-bond, and its boiling point is much reduced by comparison.

e] Dispersion forces ( dispersion forces increases with moelcular weight)

f] Hydrogen bonding [ Flourince can form hydrogen bonds whereas Chlorine cant --->Hydrogen bonding increases

Boiling point ]

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