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Unformatted text preview: CHEM 209
2/20/06 NAME: 1. (20 POINTS) Suppose a student is determining the total base content of an antacid
tablet by perfonning a back titration. He/she weighs out a 0.3022-gram portion of a tablet
whose total weight is 1.6335 grams, dissolves this in exactly 30.00mL of deionized
water, and then adds exactly 2000 mL of 0. 1000M HCl in order to bring the pH down to
2.21 This solution is then carefully back-titrated with 0.1-050M NaOH, with 3.77 mL
required to reach the equivalence point. Calculate the total base content (i.e., the number
of mmoles of base contained) of the antacid tablet. SHOW 'ALL WORK CLEARLY.
(Formula weight of HCl = 36.46 gram/mole; formula weight of NaOH = 40.00 gram/mole). 2. (30 POINTS)- (a) Write the equation for Beer’s Law and deﬁne all the terms
(including the correct units for each term).
_ i _ (b) The absorbence of a 1.0 x 10le Fe(l,10-phen)32+ solution is measured at a
wavelength of 5 ] 0 nm and found to be 0400. What is the transmittance of this solution? SHOW YOUR WORK. ________.__._____..__..._-WW._._.T_...._.____..., . .. (c) Suppose the solution in part (b) is diluted with deionized water by a factor of 2.
What are the absorbance and transmittance of the diluted solution? SHOW YOUR WORK. 3. (14 POINTS) Sketch the shape of the titration curves expected for the following titrations:
(a) BC] with NaOH
(b) KI-IP with NaOH '
mL NaOH 4. (16 POINTS) What quantities are plotted on the x— and y—axes of: x»axis (a) a chromatogram? (b) a calibration curve? y-aXis Huawhﬁw .r‘ w W 5. 0 POINTS) Deﬁne the term “retention time”. What'is its principal use in GO
analysis? - 6. POINTS) Write the equilibrium constant expressions for the folloWing balanced '
chemical reactions: _ (a): 2Mn04' + 5H3A303 + 6H+ —-——> 2Mn2+ +5H3AsO4 +3H20 K: (b) H3P04 + 3H20 --——> 9043' + 3H30+ K = BO? _[_]S QUESTION [10 POINTS} Suppose that your teaching assistant, while working
on ‘s/her MS degree in Chemistry, discovers a new compound X which might be used to
remove mercury ng (which is toxic) from contaminated water samples according to the
following balanced reaction; Hg“ + 2 X a? tax? The TA tries to determine the numerical value of the equilibrium constant by mixing 50
ml of 0.10M Hg With 50 ml of 0.20M X, allowing the reaction to occur and reach
equilibrium, and then measuring the resulting Hng2+ concentration as 0.045M. Help your TA to get his/her degree by completing the calculation needed to evaluate 'K
for the above reaction. SHOW YOUR WORK. . W—.m__mvmW—_q___._. ._......_._.H.... ‘ . . ...
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- Spring '07
- Chemistry, Chemical reaction, TA, Equivalence point, total base content