HOUR EXAM #2

Hour Exam #3

NAME (Please Print) _______________________________________________________________

Name of your Professor ____________

Lecture Section _______ ( List-1, Ekman-2, Hall-3, Phillips-4 )

School (A&S, Eng., Other) ________

I pledge on my honor that I have neither given nor received improper aid on this examination.

_______________________________________________
Signature

You will have exactly two hours to complete your exam.

Before you begin, CAREFULLY READ AND FOLLOW THE INSTRUCTIONS BELOW.

Instructions

Check to see that your exam contains all seven pages.
Show all work neatly and completely to receive partial credit.
Write your answers clearly and legibly. Answers not clearly written will be marked wrong.
Include units with answers.
Direct any questions to the supervising instructor or graduate student proctors.

Equations and constants

g = 9.807 m/s²
R = .08206 Latm/molK
R = 8.314 J/mol
R = 8.314 kgm²/s²molK
1 u = 1.66 x 10^-27 kg
avg. KE = (3/2)RT
u_rms = (3RT/molar mass)^1/2
(P + a(n/V)²)(V nb) = nRT

I. True/False check the appropriate blank (2 points each 10 points total)

True False

1. Real gases deviate from ideal gas behavior at both low temperatures and low pressures.

________ ________

2. The process of reduction must always accompany the process of oxidation..
________ ________

3. When comparing two liquids, the substance with the higher vapor pressure will have the lowest normal boiling point.
________ ________

4. As a gas escapes a vessel, the temperature of the gas decreases if the pressure and volume inside the vessel are kept constant.
________ ________

5. Intermolecular forces (van der Waals forces) are weaker than covalent bonds.
________ ________

II. Select the one best match for the following terms. (2 points each 14 points total)

1. Ion-dipole interaction ________

2. The oxidation number of Br in HBrO₄ ________

3. CH₃COOH is an example of a

________

4. Dispersion forces
________

5. The oxidation number of C in C₂H₄O₂
________

6. KOH is an example of a
________

7. The oxidation number of H in CaH₂
________

A) Strong acid G) -1 M) +8

B) Weak acid H) 0 N) The attraction between the permanent dipole moments of polar molecules.

C) Strong base I) +1 P) The attraction between instantaneous charge separations in electron clouds due to electron movement.

D) Weak base J) +2 Q) The attraction most responsible for the dissociation of salts into ions in aqueous solution.

E) Base anhydride K) +4 R) The repulsions between molecules that keep the molecules as widely separated as possible.

F) Acid anhydride L) +7 S) The attraction caused when an ion induces a dipole moment in a non-polar molecule.

III. Multiple choice. For the following questions pick the best possible answer
(5 points each, 25 points total). If you circle two answers, one of which is correct, you will receive 2 points.

The spectator ions in the following reaction are?

Al(OH)₃ (s) + 3 HNO₃ (aq) à Al(NO₃)₃ (aq) + 3 H₂O (l)
1. Al³⁺, NO₃^-
2. H⁺, NO₃^-
3. H⁺
4. NO₃^-
5. none of the above
The UF₆ molecule is approximately 175 times more massive than molecular hydrogen. Both substances are gases at 500 K. If 0.001 moles of each gas were confined in separate 10 L containers at 500 K the pressure of the UF₆ would be?
1. much greater than the H₂ pressure.
2. much less than the H₂ pressure.
3. the same as the H₂ pressure.
4. exactly 5 times greater.
5. not enough information given to determine the answer
Which of the following statements about strong acids is true?
1. All strong acids have H atoms bonded to electronegative O atoms.
2. Strong acids are completely (100%) ionized in water.
3. Strong acids are very concentrated acids.
4. Strong acids are oxidized during reactions with bases.
5. All of the above.
The formula for hydrobromic acid is
1. HBr
2. H₂Br
3. HBrO₃
4. HBrO₄
5. none of the above
Which of the following is an example of a redox reaction?
1. 3 Na₂S (aq) + Fe₂(SO₄)₃ (aq) à 3 Na₂SO₄ (aq) + Fe₂S₃ (s)
2. 2 Mn⁺³ (aq) + 2 H₂O (l) à Mn⁺² (aq) + MnO₂ (s) + 4 H⁺ (aq)
3. P₂O₅ (s) + 3 H₂O (l)à 2 H₃PO₄ (aq)
4. H₂SO₄ (aq) + Ca(OH)₂ (aq) à CaSO₄ (aq) + 2 H₂O (l)
5. none of the above

IV. Short answer / fill in the blank.

1. (10 pts total) Phosphorous forms trihalides with each of the halogens. At room temperature one is a gas, two are liquids and one is a solid.

(2 pts) Which of the phosphorous trihalides (PF₃, PCl₃, PBr₃, PI₃) is the solid?

(4 pts) What are the two types of intermolecular forces that exist for the phosphorous trihalides? (Be specific)

(4 pts) In three sentences or less explain why the trihalide you predicted to be a solid is a solid and the other trihalides are not solids.

2. (6 pts) Refer to the generic phase diagram below. Label the diagram indicating the phases, special curves and points.

____________________

____________________

____________________

____________________

____________________

____________________

3. (6 pts) For the following reactions write the NET ionic reaction. Write NR in box if no reaction takes place.

Sodium hydroxide reacting with copper (II) chloride in water.

Ammonium sulfate reacting with barium chloride in water.

V. Problems. Put final answer in box. Show your work for full credit.

1. (6 pts) Airbags are inflated with nitrogen gas produced by the decomposition of sodium azide shown below. How much sodium azide is needed to fill an air bag with a volume of 40.0 L to a pressure of 1.20 atm at a temperature of 25.0 °C?

2 NaN₃ (s) à 2 Na (l) + 3 N₂ (g)

2. (6 pts) A solution of potassium dichromate can be used to dissolve cadmium metal, according to the following equation. How many milliliters of 1.20 M K₂Cr₂O₇ are required to react with exactly 6.00 g of Cd?

K₂Cr₂O₇ (aq) + 14 H⁺ (aq) + 3 Cd (s) à 2 Cr³⁺ (aq) + 7 H₂O (l) + 3 Cd²⁺ (aq) + 2 K⁺ (aq)

3. (6 pts total) A mixture of gases is found to contain Ar, Kr, and Ne. The partial pressure of Ar was found to be 200. torr, Kr = 300. torr and Ne = 125. torr.

(1 pt) What is the total pressure of the mixture of gases?

(2 pts) What is the mole fraction of Kr?

(3 pts) If the gas mixture remains confined to a constant volume while the absolute temperature changes from 300. K to 500. K, what is the new total pressure?

4. (6 pts) A 60.0 mL volume of gas is found to have a pressure of 1.02 atm at a temperature of 20.0 °C while having a mass of 0.101 g. What is the molar mass of the gas?

5. (5 pts) A sample of methane containing ¹²CH₄ and ¹³CH₄ is to be separated by gaseous diffusion. What is the enrichment factor? (Assume the relative atomic masses are ¹²C = 12.00 u, ¹H = 1.00 u, and ¹³C = 13.00 u)

	True	False
1. Real gases deviate from ideal gas behavior at both low temperatures and low pressures.	________	________
2. The process of reduction must always accompany the process of oxidation..	________	________
3. When comparing two liquids, the substance with the higher vapor pressure will have the lowest normal boiling point.	________	________
4. As a gas escapes a vessel, the temperature of the gas decreases if the pressure and volume inside the vessel are kept constant.	________	________
5. Intermolecular forces (van der Waals forces) are weaker than covalent bonds.	________	________

1. Ion-dipole interaction	________
2. The oxidation number of Br in HBrO₄	________
3. CH₃COOH is an example of a	________
4. Dispersion forces	________
5. The oxidation number of C in C₂H₄O₂	________
6. KOH is an example of a	________
7. The oxidation number of H in CaH₂	________

A) Strong acid	G) -1	M) +8
B) Weak acid	H) 0	N) The attraction between the permanent dipole moments of polar molecules.
C) Strong base	I) +1	P) The attraction between instantaneous charge separations in electron clouds due to electron movement.
D) Weak base	J) +2	Q) The attraction most responsible for the dissociation of salts into ions in aqueous solution.
E) Base anhydride	K) +4	R) The repulsions between molecules that keep the molecules as widely separated as possible.
F) Acid anhydride	L) +7	S) The attraction caused when an ion induces a dipole moment in a non-polar molecule.

CHEMISTRY 102A Fall, 1999