Question 1

Which of the following molecules has the highest boiling point, and why?

$\mathrm{C_3H_8}$ (propane), $\mathrm{CH_3OCH_3}$ (dimethyl ether), or $\mathrm{CH_3CHO}$ (acetaldehyde)?

Accepted Answer

$\mathrm{CH_3CHO}$, because it has moderate polarity leading to stronger dipole-dipole interactions.

Question 2

Why does water ($\mathrm{H_2O}$) have a much higher boiling point than hydrogen sulfide ($\mathrm{H_2S}$), even though both are group 16 hydrides?

Accepted Answer

Because $\mathrm{H_2O}$ forms stronger hydrogen bonds due to its high polarity.

Question 3

Which intermolecular force is primarily responsible for the high boiling point of HF compared to HCl?

Accepted Answer

Hydrogen bonding

Question 4

Given the following molecules, which would be most soluble in water and why?

$\mathrm{C_3H_8}$, $\mathrm{CH_3OCH_3}$, $\mathrm{CH_3CHO}$

Accepted Answer

$\mathrm{CH_3CHO}$, because its moderate polarity allows it to interact with water's polarity.

Question 5

Which statement best explains why iodine ($\mathrm{I_2}$) has a higher boiling point than fluorine ($\mathrm{F_2}$)?

Accepted Answer

Iodine has a larger molecular mass, leading to stronger dispersion forces.

Question 6

A sealed container contains liquid ether, ethanol, and water at the same temperature. Which substance will have the highest vapor pressure and why?

Accepted Answer

Ether, because it has the weakest intermolecular forces.

Question 7

Which of the following best describes the relationship between molecular size and boiling point for non-polar molecules?

Accepted Answer

Boiling point increases as molecular size increases due to stronger dispersion forces.

Question 8

Why does n-pentane have a higher boiling point than 2-methylbutane, even though both have the same molecular formula ($\mathrm{C_5H_{12}}$)?

Accepted Answer

n-pentane has a larger surface area, leading to stronger dispersion forces.

Question 9

Which of the following statements about solubility is correct?

Accepted Answer

Polar substances dissolve best in polar solvents due to similar intermolecular forces.

Question 10

A student claims that the boiling point of a substance is only determined by its molecular mass. Which example disproves this claim?

Accepted Answer

Comparing $\mathrm{C_3H_8}$ and $\mathrm{CH_3CHO}$, which have similar masses but different boiling points due to polarity.

Question 11

Which factor most strongly increases the melting point of a non-polar molecule?

Accepted Answer

Increasing the molecular mass, which enhances dispersion forces.

Question 12

Which of the following best explains why oil does not dissolve in water?

Accepted Answer

Oil is non-polar and water is polar, so their intermolecular forces are not compatible.

Question 13

Which molecule would you expect to have the lowest vapor pressure at room temperature: water, ethanol, or ether? Explain.

Accepted Answer

Water, because it has the strongest hydrogen bonding.

Question 14

Which of the following molecules can form hydrogen bonds with water?

Accepted Answer

$\mathrm{CH_3OCH_3}$ (dimethyl ether)

Question 15

A chemist is designing a new solvent for a polar compound. Which property should the solvent have to maximize solubility?

Accepted Answer

High polarity to match the solute's intermolecular forces.

Question 16

Which of the following best describes the effect of increasing surface area on dispersion forces?

Accepted Answer

Increasing surface area increases dispersion forces, leading to higher boiling points.

Question 17

Which molecule would have the highest melting point: $\mathrm{F_2}$, $\mathrm{Cl_2}$, $\mathrm{Br_2}$, or $\mathrm{I_2}$? Why?

Accepted Answer

$\mathrm{I_2}$, because it has the largest molecular mass and strongest dispersion forces.

Question 18

Which of the following is NOT a consequence of strong intermolecular forces in a liquid?

Accepted Answer

High rate of evaporation

Question 19

A student mixes ethanol and water. What type of intermolecular force is primarily responsible for their miscibility?

Accepted Answer

Hydrogen bonding

Intermolecular Forces and Physical Properties in Organic Chemistry

Study Guide - Practice Questions