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Chemistry 141
Second Exam
Fall, 1994
Constants:
c = 2.998 x 108 m sec-1 h = 6.626 x 10-34 J sec To = 273.2 K
R = 0.08206 L atm mol-1 K-1 NA = 6.023 x 1023 mol-1
You must show all work for full credit. Please report all answers with the correct number of significant figures and units.
Part I. Review and Homework.
1. (10 points) Determine the molar concentration of a 48.0% HBr solution (density = 1.50 g/cm3).
2. (20 points) Complete the following Nomenclature Table:
a) aluminum chloride ____________________
b) ______________________ CrO3
c) potassium permanganate ____________________
d) ______________________ Fe(NO3)3 9H2O
e) barium hydroxide octahydrate ____________________
3. (6 points, Problem 4:79, page 185) Predict the product(s) of the following reactions by writing balanced equations. Identify each reaction as precipitation, acid-base, or redox.
a) H3PO4 (aq) + KOH (aq)
b) C4H8O (l) + O2 heat
Part II. Oxidation-Reduction: Balance the following oxidation-reduction equations: (You must show your work for full credit).
4. (5 points) (in base)
5. (5 points) CH2O + O2 CO2 + H2O
ACID-BASE CHEMISTRY:
6. (10 points) How many mL of 0.35M HBr are needed to neutralize 52 mL of 0.036M NaOH?
HBr + NaOH -------> NaBr + H2O
Part III. Limiting Reagent and Percent yield:
7. (7 points) How much magnesium hydroxide will be precipitated if you add 5.00 grams of magnesium nitrate (totally soluble in water) to 30.0 mL of 2.00 M NaOH solution? (MM Mg(NO3)2 = 148.3g)
Part IV. Gas Law Problems.
8. (5 points) Knowing that D= F(mass,volume) , derive an equation from the ideal gas law that will provide density from pressure, temperature, and molar mass of a gas.
9. (5 points) The mean molar mass (average molecular weight) of the gases in the atmosphere of Titan (Saturns largest moon) is 28.6 grams/mol. The surface temperature is 95K, and the pressure is 1.6 Earth atmospheres. Using the equation from #8, what is the density of Titans atmosphere?
10. (7 points) You have two balloons purchased at a recent carnival. One is filled with hydrogen, one with helium. If you assume that both gases can pass through the pores of the balloon material, which balloon will deflate faster, and how much faster?
11. (10 points) A mixture containing 0.432 mole of He, 0.357 mol of Ne and 0.104 mol of Ar is confined in a 7.00L vessel at 25C. What is the total pressure of the of the mixture?
12. (10 points) Iron is oxidized by oxygen in the air:
4Fe + 3O2 --------> 2Fe2O3
a) How many moles of oxygen will be required completely oxidize 50.0 grams of iron filings?
b) If air is 20.0% oxygen, what volume of air will be needed at one atmosphere pressure and 300K to provide the quantity of O2 determined in part A?
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