AP Classroom: Unit 3 Progress Check - AP Chemistry

The crystal structure of NaBr is represented in the diagram above. Which statement correctly compares crystalline NaBr(s) to molten NaBr(l) in terms of electrical conductivity?

Crystalline NaBr contains no freely moving electrons to conduct electricity, but molten NaBr is composed of freely moving Na+ and Br− ions, which allows it to be a good conductor of electricity.

Two sealed, rigid 5.0L containers each contain a gas at the same temperature but at a different pressure, as shown above. Also shown are the results of transferring the entire contents of container 1 to container 2. No gases escape during the transfer. Assuming ideal behavior, which statement is correct regarding the total pressure of the gases after they are combined?

The total pressure of the gases in the mixture is the sum of the initial pressures of oxygen gas and nitrogen gas because pressure only depends on the total amount of gas when volume and temperature are held constant.

What volume of a 0.100M HCl stock solution should be used to prepare 250.00mL of 0.0250M HCl?

62.5mL

A gaseous air‑fuel mixture in a sealed car engine cylinder has an initial volume of 600.mL at 1.0atm. To prepare for ignition of the fuel, a piston moves within the cylinder, reducing the volume of the air‑fuel mixture to 50.mL at constant temperature. Assuming ideal behavior, what is the new pressure of the air‑fuel mixture?

About 12atm , because the volume of the gas mixture decreased by a factor of 12.

The diagrams above represent two allotropes of solid phosphorus. Which of the following correctly identifies the allotrope with the higher melting point and explains why?

Allotrope II , because it has covalent bonds between the phosphorous atoms that are stronger than the dispersion forces between the P4 molecules in allotrope I .

Equimolar samples of CH4(g) and C2H6(g) are in identical containers at the same temperature. The C2H6(g) deviates much more from ideal behavior than the CH4(g) does. Which of the following best helps explain this deviation?

C2H6 molecules have a larger, more polarizable electron cloud than CH4 molecules do.

The diagram above shows the distribution of speeds for a sample of O2(g). Which of the following graphs shows the distribution of speeds for the same sample at a higher temperature (dashed line) ?

Diagram C

A solid compound of a group 1 (alkali) metal and a group 17 (halogen) element dissolves in water. The diagram above represents one type of solute particle present in the solution. Which of the following identifies the solute particle and best helps explain how the solute particle interacts with water molecules?

The particle is a positive ion, and the interactions are ion-dipole attractions.

A 500.mL aqueous solution of Na3PO4 (molarmass=164g/mol) was prepared using 82 gof the solute. What is the molarity of Na3PO4 in the resulting solution?

1.0M

At 10.°C, 20.g of oxygen gas exerts a pressure of 2.1atm in a rigid, 7.0L cylinder. Assuming ideal behavior, if the temperature of the gas was raised to 40.°C, which statement indicates the new pressure and explains why?

2.3atm , because the pressure P increases by the proportion 313/283 .

The gases CO2(g) and NH3(g) can be liquefied at 20°C by compressing them to sufficiently high pressures. A student claims that NH3(g) can be liquefied at a lower pressure than CO2(g) can be liquefied. Which of the following is the best justification for this claim?

CO2 is a nonpolar molecule that has London dispersion intermolecular forces that are weaker than the dipole-dipole and London dispersion forces between the polar NH3 molecules.

The structures of two allotropes of carbon are represented above. Which of the following statements best helps explain why diamond is much harder than graphite?

Carbon atoms in diamond have four covalent bonds, whereas graphite is made of layers that are held together by relatively weak dispersion forces.

Which particle diagram shown above best represents the strongest intermolecular force between two ethanol, C2H6O, molecules?

Diagram 2, because it shows the formation of a hydrogen bond between an H atom bonded to an O atom with an O atom from another molecule.

The diagrams above use arrows to represent the speed of a gas particle. Which of the diagrams best represents the speed of the particles of a gas at a fixed temperature, and why?

Diagram 2, because the particles have a variety of different speeds.

The two gas samples represented in the graph above are at the same temperature. Which of the following statements about the gases is correct?

Gas Z has a smaller molar mass than gas X .

The diagram above represents four cations, all shown to the same scale. Which cation would be predicted by Coulomb's law to have the strongest ion-dipole attraction to water, and why?

Mg2+ , because it has the largest charge-to-size ratio

The graph above shows how a particular real gas deviates from ideal behavior at very high pressures. Based on this information, which of the following is most likely the gas and gives the reason based on kinetic molecular theory?

SO2 , because it has the largest molecular volume.