AP Chemistry : AP Chemistry

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #1 : Intermolecular Forces

Put the following in order from greatest to least intermolecular forces:

I. H2O

II. LiOH

III. CO2

Possible Answers:

II>III>I

I>III>II

I>II>III

II>I>III

III>I>II

Correct answer:

II>I>III

Explanation:

LiOH displays ion-dipole IMF, H2displays hydrogen bonding, and CO2 displays dipole-dipole. Ion-dipole is greater than hydrogen bonding as an IMf, and hydrogen bonding is greater than dipole-dipole.

Example Question #2 : Intermolecular Forces

Put the following intermolecular forces in order of decreasing strength:

 

London dispersion forces; hydrogen bonds; dipole-dipole interactions; ion-dipole interactions

Possible Answers:

Hydrogen bonds

ion-dipole interactions

dipole-dipole interactions

London dispersion forces

Dipole-dipole interactions

Hydrogen bonds

Ion-dipole interactions

London dispersion forces

ion-dipole interactions

hydrogen bonds

dipole-dipole interactions

London dispersion forces

Hydrogen bonds

dipole-dipole interactions

London dispersion forces

Ion-dipole interactions

Correct answer:

ion-dipole interactions

hydrogen bonds

dipole-dipole interactions

London dispersion forces

Explanation:

Ion-dipole forces are the forces responsible for the solvation of ionic compounds in aqueous solutions, and are the strongest of the intermolecular foces. Hydrogen bonding is the second strongest intermolecular force, followed by dipole-dipole interactions. London dispersion forces are present in all solutions, but are very small and the weakest of the intermolecular forces.

Example Question #13 : Compounds And Molecules

Which of the following intermolecular forces account for the fact that noble gases can liquefy?

Possible Answers:

Ion dipole interactions

Hydrogen bonding

Dispersion forces

Dipole dipole interactions

Correct answer:

Dispersion forces

Explanation:

Noble gases are uncharged and do not have polar covalent bonds or dipole moments. The only force that could apply to them are dispersion forces.

Example Question #1 : Bonding And Forces

Which of the following is most similar to hydrogen bonding?

Possible Answers:

The slightly negatively charged sulfur atoms in H_2S are attracted to the slightly positively charged  hydrogen atom of a nearby H_2S molecule.

The chlorine bound to carbon in dichloromethane will slightly attract positive charged particles.

Water completely dissolves certain salts, like NaCl.

Two methane molecules are attracted to one another because of temporary dipoles.

A negatively charged chlorine anion in solution will attract nearby positively charged Lithium cations.

Correct answer:

The slightly negatively charged sulfur atoms in H_2S are attracted to the slightly positively charged  hydrogen atom of a nearby H_2S molecule.

Explanation:

The choice "The slightly negatively charged sulfur atoms in H_2S are attracted to the slightly positively charged  hydrogen atom of a nearby H_2S molecule" is exactly analogous to hydrogen bonding in water.

"Two methane molecules are attracted to one another because of temporary dipoles" describes London dispersion forces.

While "A negatively charged chlorine anion in solution will attract nearby positively charged Lithium cations" may sound like hydrogen bonding, it is more descriptive of  interactions between any charged particles, not charged particles within the same molecule.

"Water completely dissolves certain salts, like NaCl" does not describe bonding at all.

While "The chlorine bound to carbon in dichloromethane will slightly attract positive charged particles" sounds promising, the slight charges are not on the same molecule.

 

 

 

Example Question #3 : Intermolecular Forces

Methanol (H3COH) exhibits all of the following intermolecular forces EXCEPT __________.

Possible Answers:

London dispersion forces

Hydrogen bonding

Ionic bonding

Dipole-dipole interactions

Correct answer:

Ionic bonding

Explanation:

Methanol is not an ionic molecule and will not exhibit intermolecular ionic bonding.

Methanol is polar, and will exhibit dipole interactions. It also contains the -OH alcohol group which will allow for hydrogen bonding.

Example Question #15 : Compounds And Molecules

Which of the following intermolecular forces creates the strongest relative attraction?

Possible Answers:

Hydrogen bonding

Dispersion forces

Dipole-ion interactions

Dipole-dipole interactions

Correct answer:

Dipole-ion interactions

Explanation:

Dipole-ion interactions (an attraction between an ion and a neutral, but polar atom) are the strongest intermolecular forces listed. Ion-ion forces (attraction between two ions) are the strongest interactions overall.

Hydrogen bonding, an attraction between a hydrogen atom and a highly electronegative atom like fluorine, oxygen, or nitrogen, is the second strongest interaction listed.

The third strongest listed is dipole-dipole interactions, an attraction between two polar molecules, followed by dispersion forces, temporary shifts in the electrons of a molecule.

Example Question #4 : Intermolecular Forces

Which intermolecular force is responsible for the high surface tension of water?

Possible Answers:

Hydrogen bonding

Dispersion forces

Covalent bonding

Van der Waals forces

Correct answer:

Hydrogen bonding

Explanation:

Hydrogen bonding is what holds the hydrogen in one molecule of water to the oxygen in another molecule. Surface tension is a measure of the difficulty to disturb the surface of a liquid. The strong intermolecular connections created by hydrogen bonding makes it hard to disrupt adjacent molecules and break the water surface.

Most key properties of water are attributed to its hydrogen bonding.

Example Question #11 : Intermolecular Forces

What intermolecular forces can be found in a molecule of ethene?

Possible Answers:

London dispersion forces only

London dispersion forces, hydrogen bonding, and dipole-dipole attraction

Dipole-dipole attraction and ionic bonding

London dispersion forces and dipole-dipole attraction

London dispersion forces and hydrogen bonding

Correct answer:

London dispersion forces only

Explanation:

Ethene is an organic molecule composed of two carbon atoms, joined by a double bond, and four hydrogen atoms.

Ethene, like all molecules, exhibits London dispersion forces. This molecule, however, has no net dipole moment, so it will not exhibit dipole-dipole attraction. Also, even though it contains hydrogens, it does not exhibit hydrogen bonding. To exhibit hydrogen bonding, the hydrogen atoms must be attached to more electronegative atoms, namely nitrogen, fluorine, or oxygen. Finally, ionic bonding is only present in ionic compounds, not organic compounds.

Example Question #12 : Intermolecular Forces

Which of the following has the highest boiling point?

Possible Answers:

Correct answer:

Explanation:

Ionic bonds are the strongest type of bonds, followed by covalent bonds, hydrogen bonds, and lastly, van Der waals forces.

Example Question #13 : Intermolecular Forces

Which of the following substances has a higher boiling point?

Dipropyl Ether Untitled_drawing

Propanol Untitled_drawing__1_

Possible Answers:

They have equal boiling points

Dipropyl ether

You must know the system temperature in order to determine the answer

You must know the system pressure in order to determine the answer

Propanol

Correct answer:

Propanol

Explanation:

Although the two molecules seem similar in structure, proponol has a higher boiling point due to the hydrogen bonding allowed by its alcohol group. This creates a strong intermolecular force, and extra energy is subsequently needed to break these bonds, resulting in a higher boiling point.

System pressure and temperature are related to boiling point, but are not necessary when comparing the properties of two molecules.

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