Exam 2--S/98

Chemistry 122S
Summer 1998
Oregon State University

Exam 2 July 30, 1998 Dr. Richard Nafshun

Name _______________________________________ Score ___________ / 100

FOR THIS EXAM, ASSUME ALL GASES BEHAVE IDEALLY

[Periodic Table of the Elements Provided Here]

Calculate the Pressure, Volume, Number of Moles, Molecular Mass, or Temperature

of an Ideal Gas--10 Points Each

1. A student fills a balloon with 0.15 moles of helium gas at 1.2 atm and 20 ° C. Calculate the volume of the balloon.

2. A student fills a 4.00 liter vessel with 3.50 grams of an unknown gas at 30.1 ° C and measures the pressure to be 1.36 atm. Calculate the molar mass of the gas.

3. A student fills a 2.0 liter balloon with helium at 20 ° C and 1.0 atm. Calculate the volume of the balloon at -78 ° C and 1.0 atm.

Determine the Volume of a Gas Produced in a Limiting Reagent Problem--10 Points

4. A student places 7.8 g of magnesium into 75.0 ml of 3.0 M HCl to produce hydrogen gas and magnesium chloride at 25 ° C and 2.0 atm. How many liters of hydrogen gas are produced?

Discuss Relative Rates of Effusion--10 Points

5. Arrange the following gases according to their INCREASING u_rms at STP. Please box your final answer.

Ar     Br₂     C₂H₆      HF     CO

Calculate the Root-Mean-Square Speed of a Gas--10 Points

6. Calculate the root-mean-square speed of carbon dioxide gas in a 2.0 liter balloon at 20 ° C and 1.5 atm.

Discuss Partial Pressures of Gases--10 Points

7. A student places 0.025 mol of CO and 0.025 mol of CO₂ into a 1.0 liter balloon at 20 ° C.

(a) The partial pressure of the CO is LESS THAN the partial pressure of CO₂.

(b) The partial pressure of the CO is THE SAME AS the partial pressure of CO₂.

(c) The partial pressure of the CO is GREATER THAN the partial pressure of CO₂.

Predict, Based on Intermolecular Forces, Physical Properties of Atoms and Molecules--10 Points

8. Based on intermolecular forces, predict which of the following molecules has the highest boiling point.

CH₄     CH₃F      CH₃OH     CH₃OCH₃

Discuss and Identify Characteristics of Phase Diagrams--10 Points

9. Below is the phase diagram for H₂O (Pressure versus Temperature). Draw a horizontal line across the diagram suggesting a pressure of 1.0 atm.

Discuss and Predict Relative Surface Tensions--10 Points

10. Which of the following molecules exhibits the highest surface tensions?

H₂O (l)     CH₃CH₂OCH₂CH₃ (l)     C₆H₁₄ (l)     N₂ (l)