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Unformatted text preview: CHEM 209
Final Exam 2
2/21/05 NAME: 1. (20 POINTS) Suppose a student is determining the total base content of an antacid
tablet by performing 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 20.00 mL ofO. 1000M HCl in order to bring the pH down to
2.2. This solution is then carefully back-titrated with 0.1050M NaOH, with 3.77 mL
required to reach the equivalence point. Calculate the total base content (i.e., the number
of rnrnoles of base contained) of the antacid tablet. SHOW ALL WORK CLEARLY.
(“Formula weight of HCl = 36.46 granilmole; 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). (b) The absorbance of a 1.0 x 10‘5M Fe(1, lO-pher‘1)32+ solution is measured at a
wavelength of 510 nm and found to be 0.400. ‘What is the transmittance of this solution? SHOW YOUR WORK. (0) 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. (20 POINT S) Sketch the shape of the titration cuives expected for the following ‘ titrations:
(a) HCl with NaOH
(b) KHP with NaOH .
-pH A y
mi. NaQI-I 4. (10 POINTS) What quantities are plotted on the x— and y-axes of: (a) a chromatogram? (b) a calibration curve? 5. (10 POINTS) Deﬁne the term “retention time”. What is its pn'ncipal use in GO
analysm? ' 6. (1Q POINTS) Write the equilibrium constant expression for the following balanced
chemical reaction: " 2+ 2- - ‘
6Fe + Orzo? + 141-? ——-> 209* + We“ + 7H20 ...
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