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13 Dec 2019

Consider the molecule acetonitrile (CH3CN)

1. Which of the following must be overcome during the boiling of acetonitrile?

1. dispersion forces

2. dipole-dipole forces

3. hydrogen bonds

Which of the following must be overcome during the boiling of acetonitrile?

1. dispersion forces

2. dipole-dipole forces

3. hydrogen bonds

2 only

1 and 3

1 and 2

1 only

1, 2, and 3

2.

Shown above are the shorthand structures of phenylacetic acid and 1-octadecylamine. Recall that lines represent two-electron bonds. Ends of lines and junctures represent carbon atoms. Finally, hydrogen atoms bonded to carbon are omitted for clarity.

The solubility of phenylacetic acid in acetonitrile is 3.87 M and the solubility of 1-octadecylamine in acetonitrile is 0.08 M

Select the response that BEST rationalizes the relative solubilities

a. The dispersion forces in 1-octadecylamine are very favorable

b. Phenylacetic acid can form hydrogen bonds with the nitrogen in acetonitrile while 1-octadecylamine cannot form hydrogen bonds with the nitrogen in acetonitrile

c. There are no favorable dipole-dipole interactions between acetonitrile and 1-octadecylamine

d. The molecular weight of phenylacetic acid is closer to the molecular weight of acetonitrile

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17 Dec 2019

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* True or false

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The following table presents the solubilities of several gases in water at 25 Ā°C under a total pressure of gas and water vapor of 1 atm. (a) What volume of CH4(g) under standard conditions of temperature and pressure is contained in 4.0 L of a saturated solution at 25 Ā°C? (b) Explain the variation in solubility among the hydrocarbons listed (the first three compounds), based on their molecular structures and intermolecular forces. (c) Compare the solubilities of O2, N2, and NO, and account for the variations based on molecular structures and intermolecular forces. (d) Account for the much larger values observed for H2S and SO2 as compared with the other gases listed. (e) Find several pairs of substances with the same or nearly the same molecular masses (for example, C2H4 and N2), and use intermolecular interactions to explain the differences in their solubilities.

The corresponding volume is

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c) The molecular weight is similar for three gases. O2 and N2 are nonpolar gases, but more water molecules surround O2 as it is larger molecule. The Oā€“O bond (double bond) is longer than Nā€“N bond (triple bond). The water attracts nonpolar gases through the weak dipole-induced dipole interactions. NO is the most soluble gas as it has polar bond and the overall molecule is polar as it is linear structure. Water dissolves it via stronger dipole-dipole interactions.

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d) N2 and CH4. Solubility of N2 is lower as N2 is smaller molecule than CH4 and less hydrated.

NO and C2H6 have similar water solubility. NO is more soluble than ethane and form dipole-dipole interactions, but the dispersion forces of ethane and water are stronger than dispersion forces between NO and water as ethane is larger, more polarizable molecule. The sum of all intermolecular interactions is similar for these two gases, leading to the similar water solubility.

NO and O2. NO is more soluble as it is polar molecule and form stronger intermolecular forces with polar solvent molecules compared to nonpolar O2 molecule.


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