Consider the following Information to answer the questions below. A. For each of
ID: 476197 • Letter: C
Question
Consider the following Information to answer the questions below. A. For each of the substances in the table above, list the kinds of intermolecular forces expected for each (DD = dipole-dipole; IDF = London dispersion forces; HB = hydrogen bonding). B. Rank the molecules from least to most polar. C. Compare the polarity of each of the molecules to the boiling points (i.e., does boiling point increase or decrease as the polarity of the molecule increases?). D. Compare the molar masses (size) of each of the molecules to the boiling points (i.e., does boiling point increase or decrease as the molar mass of the molecule increases?). E. Does the boiling point, and its comparison to polarity and molar mass, indicate which type of intermolecular force is dominant in these molecules (i.e., which type of intermolecular force explains the boiling point trend?)? Briefly indicate how you reached this conclusion.Explanation / Answer
A) London dispersion forces are present in all molecules
CH3Cl - DD +LDF
CH3Br - DD +LDF
CH3I - DD + LDF
B) CH3I < CH3Br < CH3Cl
C) Boiling point increases as polarity decreases, that is the reason why CH3I which is least polar among the
three molecules has the highest boiling point. Therefore the boiling point order will be reverse of polarity.
CH3Cl --- -24.2oC ; CH3Br --- 4.5oC ; CH3I --- 42.2oC
D) Boiling point increases as molar masses increase, because it would take more energy to break down the
bonding when mass increases.
E)The dipole-dipole moment can be used to explain the trend in the boiling point. So the dominant force
will be dipole-dipole intermolecular forces. Higher dipole moment indicates higher polarity and therefore
it has higher boiling point because it should overcome respective forces.
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