Exam 4 Review
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Allison
Chem 163
Dr. Appy
11/16/14
1. Determine the oxidation state of each element in the following compounds:
a. Cr2O7 2i. Cr: 6+
ii. O:2b. NO2
i. N:4+
ii. O: 2c. CaH2
i. Ca:2+
ii. H: 1d. SO4 2i. S: 6+
ii. O: 2e. MnO2
i. Mn: 4+
ii. O: 22. Define reduction and oxidation.
a. Reduction: a gain of electrons
i. Oxidation number goes from a higher to lower value
b. Oxidation: A loss of electrons
i. Oxidation number goes from a lower to a higher value
3. Identify the species being oxidized and reduced in each of the following
reactions:
a. 2 Cr+ + Sn4+ ----> Cr3+ + Sn2+
i. Cr+ : Oxidized
ii. Sn4+ : Reduced
b. 3 Hg2+ + 2 Fe ----> 3 Hg2 + Fe 3+
i. Hg2+ : Reduced
ii. Fe: Oxidized
c. 2 As + 3 Cl2 ----> 2 AsCl3
i. As: Oxidized
ii. Cl2 : Reduced
d. 2 NaBr + Cl2 ----> NaCl + Br2
i. Br: Oxidized
ii. Cl: Reduced
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4. Construct a battery with the following equation. Label the anode, cathode,
the flow of electrons, and a salt bridge.
Cr + 3 Ag + ----> Cr3+ + 3 Ag
5. Using the EMF series, decide which of the following redox reactions is
spontaneous.
a. 3 Ag + Au3+ ----> Au + 3 Ag+
b. Au + 3 Ag+----> Ag + Au3+
Reaction A is spontaneous because Ag is more active than Au
6. Describe the following relationships:
a. Pressure-Volume Relationship
i. Increase volume, increase pressure (inverse)
b. Pressure-Temperature Relationship:
i. Increase temperature, increase pressure (proportional)
c. Pressure-Moles (n) Relationship:
i. Increase moles (n), increase pressure (proportional)
7. Knowing these relationships, what happens when…
a. You double the absolute temperature of the gas?
i. The pressure will also double
b. You double the number of liters the container can hold?
i. The pressure will divide in half
c. You double the number of moles (n) of the gas?
i. The pressure will also double
8. If I have 4.0 moles of a gas at a pressure of 5.6 atm and a volume of 12 liters,
what is the temperature?
T= PV/nR --- (5.6 atm)(12L)/(4.0mol)(0.0821 L*atm/mol*K) = 2.0 x 102
9. If I have an unknown quantity of a gas at a pressure of 1.2 atm, a volume of
31 liters, and a temperature of 87 0C, how many moles of gas do I have?
n=PV/RT --- (1.2 atm)(31L)/( 0.0821 L*atm/mol*K)(360K) = 1.3 mol
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10. If I contain 3.0 moles of gas in a container with a volume of 60. liters and at a
temperature of 400. K, what is the pressure inside the container?
P= nRT/V --- (3.0mol)( 0.0821 L*atm/mol*K)(400.K)/(60.L) = 1.6 atm
11. If I initially have a gas with a pressure of 8.4 atm and a temperature of 35 0C
and I heat it an additional 2300C, what will the new pressure be? Assume the
volume in the container is constant.
Pf =(Pi x Tf)/Ti --- (8.4atm)(538.1K)/(308K) = 15 atm
12. A 24.5-gram sample of an unknown gas occupies a volume of 44.5 L at 273.0
0C and 0.100 atm. What is the molar mass of the sample?
mm= RTm/PV --- (0.0821 L*atm/mol*K)(546K)(24.5g)/(0.100atm)(44.5L) = 247g
13. What is the molar mass of an unknown gas if 12.04 grams of the gas occupies
7.40 L at 27.0 0C and 980 mm Hg? (1 atm=760 mm Hg)
980mmHg x (1atm/760mmHg)= 1.29 atm
(0.0821 L*atm/mol*K)(300.K)(12.04g)/(1.29atm)(7.40L) = 31.1 g
14. What happens to the pressure inside a steel container if the temperature of
the container is decreased from 25.30C to 5.20C, and the number of moles of
gas inside the container is increased from 2.32 moles to 8.63 moles? The
volume of the container is 40.0 L and the initial pressure within the container
is 170.0 atm.
Pf= (Pi x nf x Tf )/ (ni x Ti) --(170.0atm)(8.63mol)(278.2K)/(2.32mol)(298.3K) = 590. atm
15. Define:
a. Solution:
i. A homogeneous mixture of two or more substances
b. Solvent:
i. Substance present in the greatest amount
c. Solute:
i. All other substances in a solution
16. How many mL of a 1.500 M solution of NaCl do you need to obtain100.0 g of
NaCl?
100.0g NaCl x (1 mol NaCl/58.443g NaCl) x (1 L Solution/1.500 mol NaCl) x (1000
mL/ 1 L) = 1140. mL Solution
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17. A solution is prepared by mixing 100.0 g of glucose (C6H12O6) with enough
water to make 500.0 mL of solution. Calculate the molarity of the solution.
M= Moles Solute/Liters Solution
(100.0g C6H12O6) x (1mol C6H12O6/180.2g C6H12O6) = 0.5549 mol
0.5549 mol / 0.5000 L = 1.110 M
18. How many milliliters of the solution in Question 17 are needed to provide
35.0 grams of glucose?
(35.0 g C6H12O6) x (1 mol C6H12O6/180.2 g C6H12O6) = 0.194 mol
L = mol/M
(0.194 mol / 1.110 M) = 0.175 L solution x 1000mL = 175 mL
19. Describe how you would prepare 250.0 mL of a 0.300 M solution of KCl from
solid KCl and water.
Moles = M x L
(0.300 mol/1 L) x (0.250 L) = 0.0750 mol KCl
0.0750 mol KCl x (74.55g KCl/1 mol KCl) = 5.60g KCl is needed to prepare 250.0
mL of a 0.300 M solution.
20. Calculate the percent by mass of a solution that is prepared by mixing 35.0
grams of ethanol (C2H5OH) and 150.0 grams of water.
(35.0 g ethanol / 150.0 grams water) x 100% = 18.9%
21. Calculate the percent by volume of a solution that contains 25.0 mL of
ethanol in 100.0 mL of a solution.
(25.0 mL ethanol / 100.0 mL solution) x 100% = 25%
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