CHE 230
Review Worksheet – Exam #2
Name ____________________
1.
Statistics
a.
The following data compares the density of Pepsi using a buret and a micropipette. Use statistics to
determine if the two tools give similar results after removing any statistically significant outliers.
Trial
1
2
3
4
5
Buret Micropipet
1.047
1.174
1.03
1.03
1.03
1.05
1.01
1.06
1.033
1.00
b. The intoxilyzer is also used to test DUI suspects. Five different people were tested by GC (the courtapproved method) and by the intoxilyzer. The results are provided below. Should the results from the
intoxilyzer stand up in court? Explain.
Suspect
A
B
C
D
E
GC
0.052
0.105
0.083
0.008
0.037
Intoxilyzer
0.045
0.091
0.081
0.005
0.029
2. Equilibrium
a. Write out the reaction and Kf expression for the complexation between EDTA and Fe(III).
b. Is this a product-favored or reactant-favored reaction? Explain.
c. How would each of the following changes shift the equilibrium?
 Addition of aqueous iron (III) nitrate solution
 Addition of sodium hydroxide to precipitate out the iron
 Addition of aqueous zinc (III) nitrate solution (which will compete with the iron for
complexation)
 Cooling the reaction (assume the complexation reaction is exothermic)
3. Gravimetric analysis/Solubility
a. Calculate the number of grams of elemental sulfur expected from reacting 1.3423 g KMnO4 with an
excess of H2S in a sulfuric acid solution. The reaction is:
5H2S + 2KMnO4 + 3H2SO4  K2SO4 + 5S (s) + 2MnSO4 + 8H2O
b. A 0.8680 g sample of a powdery white material containing oxalate was dissolved, and the oxalate was
precipitated at CaC2O4, which was subsequently filtered and ignited to CaCO3. The CaCO3 was weighed
after cooling in a dessicator. Its weight was 0.1794 g. What is the percentage of oxalate in the original
sample?
c.
Calculate the solubility of aluminum hydroxide in water at room temperature (in g per 100 mL).
d.
How would each of the following affect the solubility of aluminum hydroxide in a saturated solution
(more dissolved, more precipitates, or no effect)?
a.
b.
c.
d.
e.
Increasing the pH
Lowering the pH
Adding solid sodium chloride
Adding solid aluminum hydroxide
Heating the solution
4. Acids and bases - Calculate the pH of each of the following
a. 0.20 M formic acid
b. 0.20 M ammonium chloride
c. a mixture of 50.0 mL of 0.20 M ammonium chloride and 50.0 mL of 0.15 M ammonia
d. solution from part c + 2.5 mL of 0.010 M sodium hydroxide
5. Titration
a. 25.0 mL of 0.250 M hydrochloric acid is being titrated with 0.300 M potassium hydroxide. Calculated
the pH when:
 10 mL of titrant is added
 25 mL of titrant is added
 How much titrant is required to reach the equivalence point?
 What is the pH at the equivalence point?
b. 25.0 mL of 0.250 M formic acid is being titrated with 0.300 M potassium hydroxide. Calculated the
pH when:
 10 mL of titrant is added
 25 mL of titrant is added
 How much titrant is required to reach the equivalence point?
 Is the pH at the equivalence point less than 7, equal to 7, or greater than 7? Explain.