Chem 200 Exam 3 Review Problems Spring 2009
NOTE: These are just some of the problem types that may appear on Exam 3. Review your
quizzes, notes (especially packet problems) and homework also. The exam will cover material from:
Ch 9 (9.5), Ch 10 (all), Chp 11 (11.1 – 11.2), Chp 5 (5.1 – 5.6) and Ch 12 (12.1 – 12.5). I will give you
the rms speed equation, Graham's law of effusion equation, the Clausius Clayperon eq and any
constants. You need to know the other gas laws (Combined, Ideal, Dalton's Partial Pressures, mole
fraction).
1. Calculate the density of nitrogen gas at 37C and 760 mmHg in grams per liter.
2. A balloon contains 10. L of a gas at 24C and 101.5 kPa. Suppose the gas in the balloon is heated to
35C. If the volume is now 12 L, what is the pressure of the gas?
3. What is the density of nitrogen gas (N2) at STP?
4. How many liters does 37 g of nitrogen gas occupy at 40C and 787 mmHg ?
5. What is the molar mass of a gas if 1.0 g occupies 2.0 L at 25C and 1.2 atm?
6. The partial pressures of CH4, N2 , and O2 in a sample of gas were found to be 100., 450., and 200.
mmHg, respectively. What is the total pressure? Calculate the mole fraction of nitrogen in the mixture.
7. Given the following equation: ZnSO3(s) 
ZnO(s) + SO2 (g)
a) What is the volume of SO2(g) produced at STP when 150. grams of ZnSO3(s) are consumed?
b) How many liters of SO2(g) could be obtained at 40ºC and 787 mmHg if 150. grams of ZnSO3(s) are
consumed?
For the molecules and ions given below:
a. Draw the Lewis structure.
b. Predict the geometry of the molecule and the approximate bond angle.
c. State which hybrid orbitals would be expected for the central atom.
8. NH3
9. SF6
10. NH4+
11. BH3
12. HNO2
Would you expect the following molecules to be polar (Yes or No) ?
13. NH3
14. SO2
15. C2H6
16. H2O
17. BH3
18. There are 5 bonds in the following molecule. Label the bonds as  or  bonds.
H-CC–H
What orbitals are overlapping on each atom to cause each of the bonds you just labeled?
19. Potassium superoxide reacts with carbon dioxide to give oxygen gas:
4KO2(s) + 2CO2(g)  2K2CO3(s) + 3O2(g)
You combine 16.0 g KO2 with the carbon dioxide in a 4.00L tank, in which the gas pressure (of CO2) is
1.24 atm at 23.0C. What is the pressure of the oxygen formed if captured in a 2.50 L flask at 25.0C ?
(BIG HINT: what's the limiting reactant?)
20. Draw the Lewis structure of NO3- giving all possible resonance forms.
21. What is the molar mass of a gas that effuses at 1/3 the rate of helium?
22. What is the root mean square speed of H2 molecules at 50C ?
23. A sample of Kr gas escapes through a tiny hole is 87.3 sec. How long would it take an identical
sample of Ne gas to effuse under the same conditions of T and P? (hint: how are rate and time related?)
24. Describe, in any order, the postulates of the Kinetic Molecular Theory.
25. This is the structure of acetaminophen, found in Tylenol:
O
HO
N
H
C
CH3
a) Give the hybridization and geometry of each C and N in the molecule (remember the ring represents 6
C's, with alternating double bonds and H's as needed for each C to have 4 bonds; the N and O's have
lone pairs)
b) Calculate the formal charge of each O and N in the structure.
26. The normal boiling points of some substances are given below. Explain why these BP's are
different:
diethylether (CH3CH2OCH2CH3) BP 34.5C (The chain structure is C-C-O-C-C with the H’s on the
Cs)
ethanol (CH3CH2OH) BP 78C (The OH group is bonded to the rightmost C)
ethylene glycol (CH2(OH)CH2(OH) ) BP 197.2C (each OH is bonded to a C by C-O-H bonding)
27. Which of the following molecules can form hydrogen bonds?
a. CH4
b. H2O
c. NH3
d. HI
e. DNA
f. H2
28. For the molecules above that do not form H-bonds, which type or intermolecular force
predominates?
29. Explain how intermolecular forces influence the properties of liquids. In your explanation, describe
at least 3 liquid properties.
30. What is vapor pressure, how is it related to intermolecular forces and the boiling point of a liquid?
31. What condition must be met for a liquid to boil? What is meant by "normal boiling point"?
32. What is surface tension? viscosity?
33. Draw a sketch of the heating curve for water. Show where Hvap and Hfus fall on your curve.
34. What is a triple point? Draw an example phase diagram to illustrate your definition.
35. Calculate the heat (in kJ) needed to transform 10.0 g of ice at -10.0°C into steam at 110.0°C. Look
up all necessary specific heats and enthalpies in the packet or text.
36. What quantities are graphed on the x and y axis when using the Clausius – Clayperon equation?
What info can we get from the slope of the resulting line?
37. At 34.1°C, the vapor pressure of water is 40.1 torr. What is the vapor pressure at 85.5°C? Use 40.7
kJ/mol at the Hvap of water.
38. If a gas is collected “over water” what must you take into account when doing any calculations
involving the gas?
True or False:
1. Liquids have definite shape and volume.
2. The density of ice is less than the density of water.
3. Hydrogen bonds are stronger than covalent bonds.
4. Liquids have lower densities than gases.
5. The atoms or molecules that make up a solid have no motion.
6. Solids have little or no compressibility.
7. Evaporation is an exothermic process.
8. A phase change from the solid to the liquid phase is called sublimation.
9. London Dispersion forces occur between all molecules.
10. When the volume of a gas is doubled at constant temperature, the pressure doubles.
11. According to the KM theory, collisions between gas molecules are inelastic.
12. According to the KM theory, the volume of gas particles is small compared with the volume of the
volume of the container they occupy.
13. It is possible for water to boil at room temperature (25C).