AP Chemistry : Hydrogen Bonding

Study concepts, example questions & explanations for AP Chemistry

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Example Questions

Example Question #1 : Hydrogen Bonding

Which of the following contain(s) intramolecular hydrogen bonding?

I. NH3

II. HF

III. HCOH

IV. CH3CH2CH2OH

Possible Answers:

I only

II and I

II and IV

I, II, III, IV

I, II, IV

Correct answer:

I, II, IV

Explanation:

H bonding is when a H is bonded to either N, O, or F. In the third molecule, the O is only double-bonded to the C; it is not bonded to a single H. All other choices have a N, O, or F bonded to a H

Example Question #31 : Bonding And Forces

Which of the following best explains hydrogen bonding?

Possible Answers:

Hydrogen does not have any electrons

Electronegative atoms carry most of the electrons in the shared pairs when they are bonded to hydrogen

There are too many electrons in a solution, so H atoms interact with them

The covalent bonds between other atoms are hydrogen are called hydrogen bonds

Correct answer:

Electronegative atoms carry most of the electrons in the shared pairs when they are bonded to hydrogen

Explanation:

Electronegative atoms disproportionately pull covalently bonded electrons toward themselves, which leaves hydrogen with partial positive character. 

Example Question #1 : Hydrogen Bonding

Hydrogen bonding can occur between which two molecules?

Possible Answers:

Methane and water

Methanol and methane

Hydrogen bonding can not occur between any of these combinations

Water and hydrogen gas

Methanol and water

Correct answer:

Methanol and water

Explanation:

For hydrogen bonding to occur there must be a molecule with a hydrogen bonded to either F,O,N. This is present in water and methanol which both have O-H bonds. There can be hydrogen bonding between two water molecules, and there can be hydrogen bonding between two methanol molecules. The key to this problem is recognizing that it is asking for a situation in which hydrogen bonding is occuring between two separate molecules.  

Hydrogen bonding is the association of a hydrogen and one of the three most electronegative elements F,O,N of neighboring molecules. The hydrogen, because it is bonded to one of these elements, aquires a partially positive charge, F,O, or N develops a partially negative charge. The partially positive hydrogen will associate, not bond, with the F,O, or N of a seperate molecule. Remeber that hydrogen bonding is an intermolecular property, so it is occuring between separate molecules.  

Example Question #2 : Hydrogen Bonding

Which of the following molecules is not capable of hydrogen bonding?

Possible Answers:

Correct answer:

Explanation:

When hydrogen is bonded to a highly electronegative atom (such as nitrogen, oxygen, and fluorine), the electrons are pulled more closely to the electronegative atom than to the hydrogen nucleus. This results in a partially positive charge on the hydrogen atom, which allows it to attract partially negative charged atoms on other molecules. This type of intermolecular force is called a hydrogen bond. 

Carbon and hydrogen have very similar electronegativities, so the electrons are equally shared. This makes methane a nonpolar molecule. As a result, it is incapable of hydrogen bonding with other molecules.

Example Question #4 : Hydrogen Bonding

To which of the following atoms can hydrogen be bonded to in order for hydrogen bonding to be exhibited?

Possible Answers:

Fluorine

Astatine

Bromine

Chlorine

Iodine

Correct answer:

Fluorine

Explanation:

Hydrogen bonding only occurs when hydrogen is bound to either oxygen, nitrogen, or fluorine. Only these atoms form a bond with hydrogen polar enough so hydrogen bonding to occur.

Example Question #6 : Hydrogen Bonding

For which substance are the intermolecular forces the strongest?

Possible Answers:

Correct answer:

Explanation:

 may participate in hydrogen bonding, which is one of the strongest intermolecular forces. Hydrogen bonding increases a substance's boiling point, and lowers its vapor pressure.

Example Question #7 : Hydrogen Bonding

A pure sample of an unknown substance is subjected to a series of tests to determine its identity. It is found to have a significantly higher boiling point than a sample of another substance that is approximately the same molecular weight and has a very similar atomic composition.  

Which of the following would best account for this difference?

Possible Answers:

The configuration of the atoms in the unknown substance allows for hydrogen bonding.

The configuration of the atoms in the known substance allow for hydrogen bonding.  

None of the other answers

The configuration of the atoms in the unknown substance makes it much less polar

The configuration of the atoms in the unknown substance is more branched

Correct answer:

The configuration of the atoms in the unknown substance allows for hydrogen bonding.

Explanation:

Differences in the physcal properties of substances is often due to differences in molecular structure.  Intermolecular forces can have profound effects on physical properties such as boiling point.  Substances with the same molecular formula can actually behave quite differently based on how the atoms in these substances are connected.  Hydrogen bonding is a strong intermolecular force that often leads to higher boiling points in substances that can hydrogen bond when compared to substances of similar molecular weights that cannot hydrogen bond with one another.  Thus the presence of hydrogen bonding in the unknown substance is the best answer.  

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