Chem Quizes Unit 3

A sample of 0.010 moles of oxygen gas is confined at 127 °C and 0.80 atmospheres. What would be the pressure of this sample at 27 °C and the same volume?

0.60 atm

A gaseous mixture containing 7.0 moles of nitrogen, 2.5 moles of oxygen, and 0.50 mole of helium exerts a total pressure of 0.90 atmosphere. What is the partial pressure of the nitrogen?

0.63 atm

A flask contains 0.25 mol of SO2(g), 0.50 mole of CH4(g), and 0.50 mole of O2(g). The total pressure of the gases in the flask is 800 mm Hg. What is the partial pressure of the SO2(g) in the flask?

160 mm Hg

An equimolar mixture of N2 (g) and Ar (g) is kept inside a rigid container at a constant temperature of 300 K. The initial partial pressure of Ar in the mixture is 0.75 atm. An additional amount of Ar was added to the container, enough to double the number of moles of Ar gas in the mixture. Assuming ideal behavior, what is the final pressure of the gas mixture after the addition of the Ar gas?

2.25 atm, because doubling the number of moles of Ar doubles its partial pressure.

The nonvolatile compound ethylene glycol, C2H6O2, forms nearly ideal solutions with water. What is the vapor pressure of a solution made from 1.00 mole of C2H6O2 and 9.00 moles of H2O if the vapor pressure of pure water at the same temperature is 25.0 mmHg?

22.5 mmHg

A 2 L sample of N2 (g) and a 1 L sample of Ar (g), originally at 1 atm and 0oC, are combined in a 1 L tank. If the temperature is held constant, what is the total pressure of the gases in the tank?

3 atm

The density of an unknown gas is 4.20 grams per liter at 3.00 atmosphers pressure and 127oC. What is the molecular weight of this gas? (R = 0.0821 liter-atm/mole-K)

46.0

A 2.00-liter sample of nitrogen gas at 27°C and 600. millimeters of mercury is heated until it occupies a volume of 5.00 liters. If the pressure remains unchanged, the final temperature of the gas is

477 °C

Equal masses of He and Ne are placed in a sealed container. What is the partial pressure of He if the total pressure in the container is 6 atm?

5 atm

A chemical supply company sells a concentrated solution of aqueous H2SO4 (molar mass 98 g mol-1) that is 50. percent H2SO4 by mass. At 25oC, the density of the solution is 1.4 g mL-1. What is the molarity of the H2SO4 solution at 25oC?

7.1 M

If the pressure of each gas is increased at constant temperature until condensation occurs, which gas will condense at the lowest pressure?

Butane

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

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 the CH4 molecules do.

he table below contains information about samples of four different gases at 273 K. The samples are in four identical rigid containers numbered 1 through 4.On the basis of the data provided above, the gas in container 3 could be

CH4

Which compound, chloroacetic acid or iodoacetic acid, most likely as the lower boiling point, and why?

Chloroacetic acid, because the London dispersion forces among its molecules are weaker.

The structural isomers C2H5OH and CH3OCH3 would be expected to have the same values for which of the following? (Assume ideal behavior.)

Gaseous densities at the same temperature and pressure

The London (dispersion) forces are weakest for which of the following gases under the same conditions of temperature and pressure?

H2

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.

Equal masses of three different ideal gases, X, Y, and Z, are mixed in a sealed rigid container. If the temperature of the system remains constant, which of the following statements about the partial pressure of gas X is correct?

It depends on the relative molecular masses of X, Y, and Z

A sample of an unknown gas from a cylinder is collected over water in the apparatus shown above. After all the gas sample has been collected, the water levels inside and outside the gas collection tube are made the same. Measurements that must be made to calculate the molar mass of the gas include all of the following EXCEPT

Mass of the water in the apparatus

Based on Coulomb's law and the information in the table above, which of the following anions is most likely to have the strongest interactions with nearby water molecules in an aqueous solution?

S2-

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.

A sample of C4H10 (g) is placed in a rigid vessel with a movable piston. The volume of the gas is reduced by moving the piston downward while the temperature is maintained at 25oC, as shown above. The pressure of the gas versus its volume is plotted in the graph below.Which of the following best accounts for the pressure in the vessel remaining constant as the volume decreases below 0.21 L?

Some C4H10 (g) condenses to form C4H10 (l).

A hot-air balloon, shown above, rises. Which of the following is the best explanation for this observation?

The air density inside the balloon is less than that of the surrounding air.

When a sample of oxygen gas in a closed container of constant volume is heated until its absolute temperature is doubled, which of the following is also doubled?

The pressure of the gas

Based on the data in the table above, which of the following correctly predicts the relative strength of 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 stronger coulombic attraction to water

A hydrocarbon gas with an empirical formula CH2 has a density of 1.88 grams per liter at 0 °C and 1.00 atmospheres. A possible formula for the hydrocarbon is

C3H6

This has an average atomic or molecular speed closest to that of N2 molecules at 0 oC and 1 atm.

CO

Based on the structures shown below, 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

The figure above shows that in solid hydrogen fluoride there are two different distances between H atoms and F atoms. Which of the following best accounts for the two different distances?

Difference in strength between covalent bonds and intermolecular attractions

he volume of a sample of air in a cylinder with a movable piston is 2.0 L at a pressure of P1, as shown in the diagram above. The volume is increased to 5.0 L as the temperature is held constant. The pressure of the air in the cylinder is now P2. What effect do the volume and pressure changes have on the average kinetic energy of the molecules in the sample?

The average kinetic energy stays the same.

Diagram 1 above shows equimolar species of two gases inside a container with a removable barrier placed so that each gas occupies the same volume. The barrier is carefully removed as the temperature is held constant. Diagram 2 above shows the gases soon after the barrier is removed. Which statement describes the changes to the initial pressure of each gas and the final partial pressure of each gas in the mixture and also indicates the final total pressure?

The partial pressure of each gas in the mixture is half its initial pressure; the final total pressure is half the sum of the initial pressures of the two gases.

The reaction between NO (g) and O2 (g) to produce NO2 (g) in a rigid reaction vessel is represented in the diagram above. The pressure inside the container is recorded using a pressure gauge. Which of the following statements correctly predicts the change in pressure as the reaction goes to completion at constant temperature, and provides the correct explanation?

The pressure will decrease because there are fewer molecules of product than of reactants.

Two sealed, rigid 5.0 L 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 the volume and temperature are held constant.

If 87 grams of K2SO4 (molar mass 174 grams) is dissolved in enough water to make 250 milliliters of solution, what are the concentrations of the potassium and the sulfate ions?

4.0 M 2.0 M

When 6.0 L of He (g) and 10. L of N2 (g), both at 0oC and 1.0 atm, are pumped into an evacuated 4.0 L rigid container, the final pressure in the container at 0oC is

4.0 atm