CHem unit 3 test questions

A 0.020 mol sample of MgCl2 (s) and a 0.020 mol sample of KCl (s) are dissolved in water and diluted to 200 mL. What is the concentration of Cl- in the solution?

0.30 M

A 0.20 mol sample of MgCl2 and a 0.10 mol sample of KCl are dissolved in water and diluted to 500 mL. What is the concentration of Cl- in the solution?

0.60 M

Under which of the following conditions of temperature and pressure will H2 gas be expected to behave most like an ideal gas?

500 K and 0.10 atm

Which of the following molecules is LEAST soluble in water?

CCl4

Equal volumes of solutions in two different vessels are represented above. If the solution represented in vessel 1 is KCL (aq), then the solution represented in vessel 2 could be an aqueous solution of

CaCl2 with twice the molarity of the solution in vessel 1

The survival of aquatic organisms depends on the small amount of O2 that dissolves in H2O. The diagrams above represent possible models to explain this phenomenon. Which diagram provides the better particle representation for the solubility of O2 in H2O and why?

Diagram 2, because the polar H2O molecules can induce temporary dipoles on the electron clouds of O2 molecules.

compound formula boiling point density Hexane C6H14 69 0.66 Octane C8H18 126 0.70 A student obtains a mixture of the clear liquids hexane and octane, which are miscible (able to dissolve) in all proportions. Which of the following techniques would be best for separating the two components of the mixture, and why?

Distillation because the liquids would boil at different temperatures owing to the difference in strength of their intermolecular forces

The Maxwell- Boltzmann distributions of molecular speeds in samples of two different gases at the same temperature are shown above. Which gas has the GREATER molar mass?

Gas A

The Maxwell- Boltzmann distributions of molecular speeds in samples of two different gases at the same temperature are shown above. Which gas has the SMALLER molar mass?

Gas B

Which of the following molecules is most soluble in water?

H3C-O-H

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

HF, because its molecules form hydrogen bonds

Which of the following describes the changes in the forces of attraction that occur as H2O changes phases from a liquid to a vapor?

Hydrogen bonds between H2O molecules are broken

The experimental apparatus represented to the right is used to demonstrate the rate at which gases diffuse. When the cotton balls are placed in the ends of a tube at the same time, the gases diffuse from each and meet somewhere in between, where they react. Which of the following combinations will produce a reaction closest to the center of the tube?

NH3 and CH4

Which of the following is most likely to be a solid at room temperature?

Na2S

Which is a better conductor of electricity - a 0.10 M aqueous solution of sodium sulfate, Na2SO4 or a 0.15 M aqueous solution of sodium chloride (NaCl)?

Neither, because they have the same moles of ions present in a given volume of solution.

The diagram above represents a particle in aqueous solution. Which of the following statements about the particle is correct?

The particle must be an anion because the positive end of each water molecule is pointed toward it.

You have a certain mass of helium gas in a rigid container. You add the same mass of neon gas this container. Which of the following best describes what happens? Assume the temperature is constant.

The pressure in the container increases but does not double.

You have a certain mass of neon gas in a rigid container. You add the same mass of helium gas to this container. Which of the following best describes what happens? Assume the temperature is constant.

The pressure in the container more than doubles.

Based on the data in the table above, which of the following correctly predicts the relative strength of the attraction of Zn2+, Ca2+, and Ba2+ ions to water molecules in a solution, from strongest to weakest, and provides the correct reason?

Zn2+>Ca2+>Ba2+ because the smaller ions have a stronger coulombic attraction to water

A 1.0 L sample of a pure gas is found to have a lower pressure than that predicted by the ideal gas law. The best explanation for the observation is that the molecules of the gas

are attracted to each other and do not exert as much force on the container walls as they would if they had no mutual attractions

Solid carbon tetrachloride, CCl4 , is represented by the diagram above. The attractions BETWEEN the CCL4 molecules that hold the molecules together in the solid state are best identified as

intermolecular attractions resulting from temporary dipoles

Solid carbon tetrachloride, CCl4 , is represented by the diagram to the right. The attractions WITHIN the CCL4 molecules that hold the molecules together are best identified as

nonpolar covalent bonds

Substance Equilibrium Vapor Pressure at 20 degrees C (torr) C6H6(l) 75 C2H5OH(l) 44 CH3OH(l) 92 C2H6O2(l) 0.06 Based on the data in the table above, which of the following liquid substances has the strongest/weakest intermolecular forces?

strongest- C2H6O2 (l) weakest- CH3OH (l)