Chemistry 331
First Hour Exam
2007
Physical Constants:
Speed of Light (c) 2.9979 x 108 m/s
Faraday Constant (F) 9.6485 x 104 C/mol
Plank’s Constant (h) 6.6262 x 10-34 j/s
Gas Constant (R) 8.314 j/mol K
1) Given the following standard free energies:
H2CO3
HCO3CO32H+
H2O
OH-
Go (kcal/mole)
- 607.1
- 586.8
- 527.9
0
-237.1
-157.3
Calculate the equilibrium constant for the following reaction: at 25 oC.
2-
CO3
-
+ 2 H2O  H2CO3 + 2 OH
2) You can not ignore activity coefficients for this problem, but think before you
calculate! Assume the ion size for all ions is 500 pm.
a) AgCl (pKsp = 9.74) is added to a beaker of reagent grade water.
Calculate the concentration of Ag+ and Cl- in the solution.
b) CaCO3 (pKsp = 8.35) is added to a beaker of reagent grade water.
Calculate the concentration of Ca2+ and CO32- in the solution.
c) Recalculate parts a and b if the AgCl and the CaCO3 were added to a 0.1
M NaNO3 solution instead of reagent grade water.
d) If AgCl and CaCO3 had the same Ksp, which salt would be more soluble
in 0.1 M NaNO3? WHY?
3) A chemist wants to measure the total chloride concentration in Waterville’s
drinking water.
a) Starting with 5.844 grams of dried primary standard NaCl (s) she
prepares a 1.00 L NaCl solution. A 5.000 ml aliquot of this standard is
used to standardize a AgNO3 solution, requiring 40.00 ml of the AgNO3
solution to reach the equivalence point. Switching to the water sample,
10.0 ml of tap water required 8570 L of AgNO3 to reach the endpoint.
What is the concentration of chloride in our tap water?
b) What was the chloride ion concentration after 4285, 8750 and 10000. L
of added titrant?
4) What is the molarity and the molality of a 38.0 % (w/w) hydrochloric acid
solution (density = 1.189 g/ml, molar mass HCl = 36.45 g/mol)?
5) Given only the following reagents and solutions to work with:
Water
HCl (0.1 M)
NaOH (0.1 M)
Sodium Acetate (Fwt. 82, pKa = 4.75)
Ammonium Chloride (Fwt. 53.45, pKa = 9.244)
Potassium Hydrogen Phthalate (Fwt. 204, pK1 = 2.95, pK2 = 5.41)
Describe how you would prepare a buffer solution with a pH of 9.0, a
formal concentration of 0.01 M, and a total volume of one liter. Provide specifics
on the quantities of the reagents and solutions that you would use. You do not
have a pH meter!
6) What is the pH of a 0.01 M solution of sodium acetate? You may not ignore
activity effects. (pKa of CH3COOH = 4.750, assume the ion size for all ions is 500
pm)