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23.11.2020 • 
Chemistry

A student leaves a 2.12 g piece of sodium metal sitting uncovered over the weekend. The student returns to the lab to find a shiny coating of sodium oxide on the piece of metal.
a. What substance reacted with the sodium, and where did it come from?
b. Write a balanced chemical equation for the process.
c. What type of reaction is this?
d. If the student assumes that the substance the sodium reacted with is excess, what is the
theoretical yield of sodium oxide?
2. 25.0 g of C2H6O2 (a nonelectrolyte, molar mass = 62.08 g/mole) is dissolved in 175.0 g of
water (molar mass = 18.02 g/mol) at 45.0°C. What is the vapor pressure of the solution?
P°H2O at 45°C = 71.9 mm Hg.
3. When 150. mL of a 0.2 M barium nitrate solution is added to a 200. mL of a 0.2 M potassium
chromate solution…
a. Write a balanced chemical equation for the reaction.
b. Is a precipitate present? If so, what is it?
c. How many grams of the precipitate could be formed?
d. Write the net ionic equations for the process.
e. Are there any spectator ions? If so, list them.
4. An unknown compound (11.2 mg) is dissolved in water to make 8.00 mL of solution. The
solution does not conduct electricity and has an osmotic pressure of 0.338 atm at 27.0°C.
Elemental analysis reveals the substance to be 58.55% C, 13.81% H, and 27.40% N by mass.
Determine the molecular formula of the compound. (Note: 1 atm = 760 mm Hg, 8 points)
5. Balance the following redox reaction as if it occurred in acidic solution: (8)
SO3
-2 + BrO4
-1 > SO4
-2 + Br-1
6. A solution is made by dissolving 37.80 grams of potassium sulfate (molar mass = 174.27
g/mol) into 675 mL of water (molar mass = 18.02 g/mol).
a. Determine the molarity of this solution.
b. Determine the molality of this solution
c. Estimate the value of the v’ant Hoff coefficient for this solution
d. What is the freezing point of this solution?

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