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 February 22, 1993
- (20 pts) 100.0 mL of water from a certain lake was found to contain 592.7 µg of mercury(II)
chloride. What is the concentration of mercury in a) parts per million, and b) molarity?
- (15 pts) 0.3157 g of an unknown monoprotic acid required 45.72 mL of 0.1036 M NaOH to titrate to
a phenolphthalein endpoint. What is the molecular weight of the acid?
- (15 pts) 1.3540 g of a stainless steel sample is dissolved in aqua regia (HCl + HNO3) and then the
iron is precipitated as iron(III) oxide. The precipitate, after heating to constant weight, weighed
0.7058 g. What is the percent of iron in the stainless steel?
Chemistry 242 Due Friday March 3, 1993 by 5:00 pm Exam 1 (Take Home)
Chemistry 242 Exam 2 March 12, 1993
- (15 pts) As a chemist in an analytical lab, you have been given an ore sample to analyze for nickel
content. Gravimetric analysis of 6 aliquots of the ore yielded the following percentages of Ni:
6.35%, 6.20%, 6.34%, 6.37%, 6.36%, 6.35%. What is the 99% confidence interval for this analysis?
- The following calibration data were collected in a polarographic determination of lead in a ground
water sample. (In polarography current is a linear function of the concentration.)
Calibration Curve Data
||Unknown run #
- (7 pts) Plot the calibration curve.
- (15 pts) 6 runs were made on the same unknown sample. Using linear least squares, calculate
the absolute 95% confidence interval for the lead concentration (mM) in the sample.
- (8 pts) Convert the lead concentration and absolute 95% CI of the unknown sample to units
of parts per million.
- (5 pts) What is the relative 95% confidence interval for the unknown sample?
- (10 pts) Which of the following compounds are soluble in water? Cu(CH3COO)2, Al(OH)3, BaSO4, Hg2Cl2, Pb(NO3)2
- (15 pts) Will the following form acidic, basic, or neutral aqueous solutions? For those that form
acidic or basic solutions, what is the conjugate of each?
HBrO3 NH3 SO3 -2 NO2 CH3OH
N2(g) + 3 H2(g) = 2 NH3(g) K = 760
- (25 pts) Commercially ammonia is produced by the Haber process (above). This reaction is
exothermic, but it proceeds very slowly at 25°C and 1 atm pressure even with a catalyst. What
changes in these reaction conditions would you make to optimize the yield from the reaction?
Explain your reasoning for each change.
- (25 pts) The absorbance of a saturated solution of silver chromate at 370 nm in a 1.000 cm cell is
0.321. The molar absorptivity of chromate at 370 nm is 4.79 x 103 M-1cm-1 and silver does not
absorb at 370 nm. What is the Ksp of silver chromate?
- (25 pts) What is the pH of a saturated solution of calcium hydroxide? (Ksp = 6.5 x 10-6).
Chemistry 242 Exam 3 April 19, 1993
- (15 pts) Will the following produce acidic, basic, or neutral solutions in water? Write the reactions
that justify your prediction. P2O5, NH4Cl, CH3NH2, Ca(NO3)2, Ca(NO2)2
- (10 pts) What are the strong acids and bases?
- (20 pts) For a solution containing 0.10 M KCl and 0.10 M Na2C2O4, what is:
- the charge balance equation
- the oxalate mass balance equation
- (15 pts) A 0.25 M Na2S solution is saturated with MnS. Write the complete reactions and the
equilibrium reactions for this system making no assumptions.
- (20 pts) What is the pH of 0.1 M ammonium sulfate? (for the conjugate acid/base pair: Ka =
5.6 x 10-10; Kb =1.8 x 10-5)
- (20 pts) What is the pH of a solution that is 0.10 M acetic acid and 0.11 M aluminum acetate? (for
the conjugate acid/base pair: Ka = 1.8 x 10-5; Kb = 5.6 x 10-10)
Chemistry 242 Exam 4 May 5, 1993
- (10 pts) Which of the indicators in the table above would work the best for the titration of 0.1 M
sodium hydroxide with 0.1 M hydrochloric acid? Explain your reasoning.
- (15ts) Balance the following reaction in basic solution.
(CH3)2C=O + Cr2O7 -2 = Cr+3 + CO2
- (5 pts) Which reactant in the above reaction is the oxidizing agent? Which element is oxidized?
- (15 pts) Give an ion or molecule that will reduce Br2 but will not reduce Ag+. Briefly explain how
you chose the species.
- (20 pts) What is the Ecell and Keq for Pt/Fe+2, Fe+3//I -, I3 -/Pt
- (15 pts) Gold plating is often used to provide corrosion resistance for metals. If 285 coulombs of
electricity is used to plate a 250 cm2 cone,
- what weight of gold is there on each square centimeter of the cone?
- what weight of NaAuCl4 is required to plate the cone?
- Permanganate (MnO4 -) in basic solution has an E° of 0.60 V (1/2 reaction on the table).
- (15 pts) What is the potential for the reaction if the pH is changed to 7.00?
- (5 pts) Will permanganate at pH 7.00 be a stronger or a weaker oxidizing agent than under
standard conditions? Explain your reasoning.
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Copyright© Duane E. Weisshaar, Augustana College, Sioux Falls SD
57197, January, 1998. Noncommercial redistribution permitted. (see details.)