AP Chem Unit 3.2: Properties of Solids

The table above shows the structural formulas and molar masses for three different compounds. Which of the following is a list of the compounds in order of increasing boiling points?

Butane < acetone < 1-propanol

The ionic compounds NaCl and MgS are represented by the diagrams above. Which statement correctly identifies diagram 1 and identifies the compound with the lower melting point, explaining why?

Diagram 1 represents NaCl ; it has a lower melting point than MgS because the coulombic attractions between its singly charged Na+ ions and the Cl− ions are weaker than those between the ions in MgS .

Which of the following lists the substances F2, HCl, and HF in order of increasing boiling point?

F2 < HCl < HF

Ne, HF, C2H6, CH4 Which of the substances listed above has the highest boiling point, and why?

HF, because its molecules form hydrogen bonds

The diagram above shows molecules of Br2 and I2 drawn to the same scale. Which of the following is the best explanation for the difference in the boiling points of liquid Br2 and I2, which are 59oC and 184oC, respectively?

I2 molecules have electron clouds that are more polarizable than those of Br2 molecules, thus London dispersion forces are stronger in liquid I2.

In solid methane, the forces between neighboring CH4 molecules are best characterized as

London (dispersion) forces

The enthalpy of vaporization of water is 40.7 kJ/mol. Which of the following best explains why the enthalpy of vaporization of methane is less than that of water?

Methane does not exhibit hydrogen bonding, but water does.

A 0.10 M aqueous solution of sodium sulfate, Na2SO4 , is a better conductor of electricity than a 0.10 M aqueous solution of sodium chloride, NaCl. Which of the following best explains this observation?

More moles of ions are present in a given volume of 0.10 M Na2SO4 than in the same volume of 0.10 M NaCl.

Based on the data in the tables above, which of the following statements provides the best prediction for the boiling point of NaCl?

NaCl will have a lower boiling point than NaF because the coulombic attractions are weaker in NaCl than in NaF.

Which of the following substances is a strong electrolyte when dissolved in water?

Sodium nitrate

A student is given a sample of a pure, white crystalline substance. Which of the following would be most useful in providing data to determine if the substance is an ionic compound?

Testing the electrical conductivity of an aqueous solution of the substance

A certain crystalline substance that has a low melting point does not conduct electricity in solution or when melted. This substance is likely to be

a molecular solid

The structure of one form of boron nitride is represented above. This form of boron nitride is one of the hardest substances known. Which of the following best helps explain why boron nitride is so hard?

Boron nitride is a network solid of atoms connected by covalent bonds with fixed bond angles.

Equimolar samples of CH3OH(l) and C2H5OH(l) are placed in separate, previously evacuated, rigid 2.0 L vessels. Each vessel is attached to a pressure gauge, and the temperatures are kept at 300 K. In both vessels, liquid is observed to remain present at the bottom of the container at all times. The change in pressure inside the vessel containing CH3OH(l) is shown below. Compared to the equilibrium vapor pressure of CH3OH(l) at 300 K, the equilibrium vapor pressure of C2H5OH(l) at 300 K is

lower, because London dispersion forces among C2H5OH molecules are greater than those among CH3OH molecules

Based on the data in the table above, which of the following liquid substances has the weakest intermolecular forces?

CH3OH(l)

Based on the information in the table above, which liquid, CS2(l) or CCl4(l), has the higher equilibrium vapor pressure at 25°C, and why?

CS2(l), because it has weaker London dispersion forces

Based on the structures shown above, which of the following statements identifies the compound with the higher boiling point and provides the best explanation for the higher boiling point?

Compound 2, because it forms hydrogen bonds, whereas compound 1 does not

Based on the diagram above, which of the following best helps to explain why MgO(s) is not able to conduct electricity, but MgO(l) is a good conductor of electricity?

MgO(s) consists of separate Mg2+ ions and O2− ions held in a fixed lattice, but in MgO(l) the ions are free to move and conduct electricity.

Which of the following could be the identity of a white crystalline solid that exhibits the following properties? It melts at 320°C. It does not conduct electricity as a solid. It conducts electricity in an aqueous solution.

NaOH(s)

The boiling points of the elements helium, neon, argon, krypton, and xenon increase in that order. Which of the following statements accounts for this increase?

The London (dispersion) forces increase.