1.
Which statement about intermolecular forces is true?
Correct Answer
D. None of the above
Explanation
The correct answer is "none of the above." The statement that intermolecular forces hold atoms together in a molecule is incorrect because intermolecular forces are the forces of attraction between molecules, not within a molecule. The statement that intermolecular forces are responsible for the chemical properties of matter is also incorrect because chemical properties are determined by the arrangement and bonding of atoms within a molecule. Lastly, the statement that intermolecular forces have to be overcome to decompose a substance is also incorrect because intermolecular forces do not play a role in the decomposition of a substance, which is typically a result of chemical reactions breaking the bonds within the molecule.
2.
Which statement about London dispersion forces is incorrect?
Correct Answer
D. All are correct
Explanation
The given answer states that all the statements about London dispersion forces are correct. London dispersion forces result from an asymmetric distribution of electrons, which are present in polar molecules (dipole) and are more pronounced in molecules with atoms that have high polarizability. Therefore, the answer is correct.
3.
Which of the following explains why the boiling points of hydrocarbons increase with increasing molar mass?
I. The larger mass makes molecules move slower, allowing for increased attractions
II. Hydrogen bond strength increases
III. London forces become more pronounced with a greater number of atoms.
Correct Answer
D. I and III
Explanation
The correct answer is "I and III". The boiling points of hydrocarbons increase with increasing molar mass because of two main reasons. Firstly, the larger mass of the molecules makes them move slower, allowing for increased attraction between the molecules, which leads to higher boiling points. Secondly, as the number of atoms in the molecule increases, the London forces (also known as Van der Waals forces or induced dipole-induced dipole interactions) become more pronounced. These forces are responsible for the attraction between nonpolar molecules and also contribute to the higher boiling points of hydrocarbons with larger molar masses. Hydrogen bond strength (mentioned in option II) is not applicable to hydrocarbons, as they do not contain hydrogen bonded to an electronegative atom.
4.
Vapor pressure is defined as the pressure exerted by a gas in equilibrium with its liquid. Which of the following has the highest vapor pressure?
Correct Answer
D. CH3OCH3
Explanation
The compound CH3OCH3, also known as dimethyl ether, has the highest vapor pressure among the given options. This is because it has weaker intermolecular forces compared to the other compounds. Weaker intermolecular forces allow the molecules to escape the liquid phase more easily and therefore exert a higher pressure as a gas in equilibrium with its liquid. CCl4 has stronger intermolecular forces due to its larger size and stronger London dispersion forces. CH3CH2OH (ethanol) and H2O (water) have hydrogen bonding, which is stronger than the London dispersion forces in CH3OCH3.
5.
What intermolecular force is responsible for the attraction between an ion and a polar molecule?
Correct Answer
C. Ion-dipole interaction
Explanation
Ion-dipole interaction is the correct answer because it refers to the attractive force between an ion and a polar molecule. In this type of interaction, the charged ion is attracted to the opposite partial charges on the polar molecule. This force is stronger than dipole-dipole interaction and dipole-induced dipole interaction because it involves a charged ion. Hydrogen bonding is a specific type of dipole-dipole interaction that occurs when a hydrogen atom is bonded to a highly electronegative atom like oxygen, nitrogen, or fluorine.
6.
What type of intermolecular force is responsible for the attraction between a polar molecule that induces a temporary dipole on a non-polar molecule?
Correct Answer
C. Dipole-induced dipole
Explanation
The attraction between a polar molecule and a non-polar molecule is due to dipole-induced dipole forces. In this case, the polar molecule induces a temporary dipole on the non-polar molecule, resulting in an attractive force between them. This type of intermolecular force occurs between molecules that have a permanent dipole (polar) and molecules that do not have a permanent dipole (non-polar). The temporary dipole on the non-polar molecule is caused by the shifting of electron density in response to the presence of the polar molecule.
7.
Consider the following electronegativity values (C=2.5, O=3.5, S=2.5, F=4.0, H=2.1). Which of the following has greater dipole-dipole force?
Correct Answer
C. SO2
Explanation
SO2 has greater dipole-dipole force because it has a bent molecular geometry with a lone pair on the central atom (sulfur). The oxygen atoms are more electronegative than sulfur, causing a partial negative charge on the oxygen atoms and a partial positive charge on the sulfur atom. This creates a dipole moment, resulting in stronger dipole-dipole forces compared to the other molecules listed.
8.
Consider HCl, HBr, HF, and HI. Which statement is incorrect?
Correct Answer
C. HF has the highest vapor pressure.
Explanation
Vapor pressure generally decreases as intermolecular forces increase. HF, which exhibits hydrogen bonding, would have stronger intermolecular forces compared to HCl, HBr, and HI, leading to lower vapor pressure. Therefore, HF would not have the highest vapor pressure among the given options.
9.
Which of the following is most likely a solid at room temperature?
Correct Answer
D. I2
Explanation
I2 is most likely a solid at room temperature because iodine is a nonmetal element with a higher atomic number compared to the other options (Br, F, Cl). Nonmetals tend to have lower melting and boiling points, and as we move down the halogen group, the melting and boiling points generally increase. Therefore, I2 is more likely to be a solid at room temperature compared to the other halogens.
10.
Heat of vaporization is the amount of heat required to convert unit mass of a liquid into the vapor state without a change in temperature. Which substance has the highest heat of vaporization?
Correct Answer
B. CH3CH2CH2OH
Explanation
The substance with the highest heat of vaporization is CH3CH2CH2OH. This is because CH3CH2CH2OH, also known as ethanol, has strong intermolecular forces due to the presence of hydrogen bonding. These intermolecular forces require a large amount of energy to break in order to convert the liquid into vapor. In comparison, the other substances listed do not have hydrogen bonding and therefore have weaker intermolecular forces, resulting in lower heat of vaporization.