Chemistry Unit 3

A 360. mg sample of aspirin, C9H8O4, (molar mass 180. g), is dissolved in enough water to produce 200 mL of solution. What is the molarity of aspirin in a 50. L sample of this solution?

0.0100 M

A 40.0 mL sample of 0.25 M KOH is added to 60.0 mL of 0.15 M Ba(OH)2. What is the molar concentration of OH- in the resulting solution? (Assume that the volumes are additive.)

0.28 M

A 0.20 mol sample of of MgCl2 and a .10 mol sample of KCl are dissolved in water and diluted to 500 mL. What is the concentration of Cl- in the solution?

1.0 M

How many mL of 10.0 M HCl are needed to prepare 500 mL of 2.00 M HCl?

100 mL

Given that the density of Hg at 0*C is about 14 g mL, which of the following is closest to the volume of one mole of Hg at this temperature?

14 mL

A sealed vessel contains 0.200 mol of oxygen gas, 0.100 mol of nitrogen gas, and 0.200 mol of argon gas. The total pressure of the gas mixture is 5.00 atm. The partial pressure of the argon is

2.00 atm

Based on the data in the table above, which of the following liquid substances has the weakest intermolecular forces? (See page 7 #14)

CH3OH

A 0.5 mol sample of He and a 0.5 mol sample of Ne are placed separately in two 10.0 L rigid containers at 25 *C. Each container has a pinhole opening. Which gas will escape faster through the pinhole and why?

He will escape faster because the He atoms are moving at a higher average speed than the Ne atoms.

A sample of an ideal gas is cooled from 50.0 C to 25.0 C in a concealed container of constant volume. Which of the following values for the gas will decrease? I. The average molecular mass of the gas II. The average distance between the molecules III. The average speed of the molecules

III only

At room temperature I2 is a molecular solid. What is the characteristic of I that explains this phenomenon?

It is not a good conductor of electricity because its valence electrons are localized in bonding and nonbonding pairs

The electron cloud of HF is smaller than that of F2, however, HF has a much higher boiling point (293 K) than F2 (85 K) has. What explains how the dispersion- force model of intermolecular attraction does not account for the unusually high boiling point of HF?

Liquid F2 has weak dispersion force attractions between its molecules, whereas liquid HF has both weak dispersion force attractions and hydrogen bonding interactions between its molecules

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. Explain why this happened.

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

What best helps to explain the observation that NH3 boils at -28 *C, whereas PH3 boils at -126 *C?

NH3 has hydrogen bonding that is stronger than the dipole-dipole forces in PH3

A student is given a sample of a pure, white crystalline substance. What 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

The student made the standard curve above. What most likely caused the error in the point the student plotted at 0.050 M Co2+? (See page 8 #15)

There was distilled water in the cuvette when the student put the standard solution in it.

Based on the concepts of polarity and hydrogen bonding, which of the following sequences correctly lists the compounds above in the order of their increasing solubility in water? (See page 6 #13)

X<Y<Z

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

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

At 298 K and 1 atm, Br2 is a liquid with a high vapor pressure, and Cl2 is a gas. Those observation provide evidence under the given conditions, the

forces among Br2 molecules are stronger than those among Cl2 molecules

Compared to the equilibrium vapor pressure of CH3OH at 300 K, the equilibrium vapor pressure of C2H5OH at 300 K is (See page 9 #16)

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