SELECTED INDICATOR pKa's
EQUATIONS AND CONSTANTS
A=abc A = -log T Kw = 1.01 x 10-14 = KaKb
Ecell = Ered - Eox = Eright - Eleft Eeqv, soln = (n1E1° + n2E2°)/(n1 + n2)
G = -nFE G° = -RT ln Keq E° = (0.05916/n) log Keq
E = E° - (RT/nF) ln Q = E° - (0.05916/n) log Q Esce = 0.241 V EAg/AgCl = 0.197 V
A = coul/s J = coul·V) F = 96487 coul/mole e- R = 8.314 J/mole·K
Do the following problems on the paper provided. Use only ONE SIDE of each page.
SHOW YOUR WORK. NO WORK, NO CREDIT.
LABELS AND PROPER NUMBER OF SIG FIGS.
Up to 80% of the credit for a problem will be given for correctly setting it up,
including labels on all numbers.
Chemistry 242 Exam 1 (In Class) Spring 1991
- (10 pts) What are the three major considerations for developing a gravimetric procedure?
- (10 pts) Which compounds are considered soluble in water? CuCl2, AgCl, Na2S, FeS, Al(OH)3
Pb(OH)2 (s) = Pb+2 (aq) + 2 OH - (aq)
- Consider a system at equilibrium in a beaker. After the following actions are taken and equilibrium
has been re-established, has the solubility of Pb(OH)2 increased, decreased, or remained the same?
EXPLAIN YOUR REASONING FOR EACH CASE.
- (5 pts) More Pb(OH)2 (s) is added to the solution.
- (5 pts) HCl is added to the solution.
- (10 pts) A sample of air contains 0.130 µg/L sulfur dioxide. If the density of the air is 1.19 g/L, what
is the concentration of sulfur dioxide in the air in parts per million?
- (10 pts) A 1.03 x 10-3 M solution of an unknown has a transmittance of 0.436 at 450 nm in a 2.000
cm cell. What is the absorptivity of the unknown?
Chemistry 242 Take Home Exam 1 Spring 1991
- (15 pts) As a chemist in an analytical lab, you have been given a blood serum sample to analyze for
potassium ion concentration. Determination of 6 aliquots of serum by ion selective electrode yielded
the following concentrations of K+: 153 ppm, 156 ppm, 163 ppm, 155 ppm, 154 ppm, and 154 ppm.
Calculate the relative standard deviation and the 90% confidence interval for the concentration of
- (20 pts) Nickel forms a complex with 1-(2-pyridylazo)-2-naphthol (PAN) that can be represented as
NiL2. A series of nickel standards and a solution of unknown nickel concentration were each treated
with an excess of PAN. The absorbances of each of these solutions were measured at 575 nm. (The
results are given below.) Calculate the 95% confidence interval for the concentration of nickel in the
- (15 pts) The quality control lab for Squibb routinely analyzes the vitamin tablets produced by the
company. The lab has determined that 50 g of tablets from each batch must be analyzed to obtain a
sampling standard deviation (%RSD) of 1%. The procedure they use for analysis of vitamin A
requires a 5.00 g sample. How many 5 gram samples should be analyzed to provide 95% confidence
that the average is within 3% (relative) of the true value for the batch?
Chemistry 242 Exam 2 (In Class) Spring 1991
- (18 pts) Consider 0.1 M solutions of the following: NH4Cl, CH3OH, Na2O, KClO4, HOOCCOOH, (CH3)2NH
- Which of the above compounds will make water acidic? Write Ka reactions to justify your
- Which of the above compounds will make water basic? Write Kb reactions to justify your
- (16 pts) Which of the indicators in the table above would work the best for the titration of
methylamine with hydrochloric acid? Explain your reasoning.
- (12 pts) What is the pH of 1.356E-2 M barium hydroxide?
- (6 pts) Would the pH calculated using activity coefficients be higher or lower than the pH
calculated in part a? Explain your reasoning.
- (16 pts) What is the pH of solution that is 0.0113 M calcium acetate and 0.0140 M acetic acid?
- A solution contains 0.100 M NaHC2O4.
- (8 pts) Write the charge balance equation for this system making no assumptions.
- (8 pts) Write the mass balance equation for this system making no assumptions.
- (16 pts) Which conjugate acid-base system from the Ka table above would be the best choice for
making a pH 7.00 buffer? Explain your reasoning. Consider both practical and theoretical aspects.
Don't forget that you can make buffers based on K2 or K3 too.
Chemistry 242 Exam 3 (In Class) May 8, 1991
Pt/H2 (1 atm)/CH3COOH (0.1000 M), CH3COONa (0.1000 M)//SCE
- (11 pts) Balance the following reaction in basic solution.
C6H5CH3 + MnO4 - = MnO2 + C6H5COOH
- Give an ion or molecule that will reduce I3 - but will not reduce Sn+2. Explain how you chose the
- (11 pts) When measuring pH with a glass electrode, will alkaline error cause the measured pH to be
higher or lower than the actual pH? Why?
Cl3CCOO - + H2O + 2 e- = Cl2CHCOO - + OH - + Cl -
- (11 pts) Trichloroacetate is quantitatively reduced to dichloroacetate in a solution containing 2 M
KCl, 2.5 M NH3, and 1 M NH4Cl at a potential of -0.90 V vs SCE. Electrolysis of 0.7210 g of a
sample containing trichloroacetate using the above conditions required 224.0 coulombs. What is the
weight percent of trichloroacetic acid (Cl3CCOOH) in the sample?
- 50.00 ml of 0.05000 M Fe+2 is titrated with 0.10000 M MnO4 -. The solution is buffered at pH 0.00.
The titration is followed potentiometrically by measuring the potential between a Pt electrode
dipping in the solution (reduction half cell) and an SCE reference electrode (oxidation half cell).
- (11 pts) What is the equilibrium constant for the titration reaction in the above problem?
- (11 pts) What potential will be measured after 7.00 ml of MnO4 - has been added?
- (11 pts) What potential will be measured at the equivalence point?
- (11 pts) The Ka of acetic acid is 1.75E-5. What is the E for the following cell?
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Copyright© Duane E. Weisshaar, Augustana College, Sioux Falls SD
57197, January, 1998. Noncommercial redistribution permitted. (see details.)