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CHM 241 - Exam II - Fall 2007 Example

# CHM 241 - Exam II - Fall 2007 Example - CHM!241!Fall!2007...

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1 e CHM 241 Fall 2007 Exam 2 Name___________________________________ (Print) CALCULATIONS. Show your calculation to get full credits. 1. For a weak base: , deriv ! ] " # \$ % & ( [ ] [ log BH B pKa pH 2. [Internal standard]. A solution containing 0.0837M X and 0.0666M S gave peak areas of Ax=423, As=347. To analyze the unknown, 10.0 mL of 0.146M S were added to 10.0 mL unknown, and the mixture was diluted to 25.0 mL in a volumetric flask. The measurement of this mixture gave Ax=553 and As= 582. Find the concentration of X in the unknown. 3. [Standard Addition] An unknown sample of Cu2+ gave an absorbance of 0.262 in an atomic absorption analysis. Then 1.00 mL of solution containing 100.0 ppm (= " g/mL) Cu2+ was mixed with 95.0 mL of unknown, and the mixture was diluted to 100.0 mL in a volumetric flask. The absorbance of the new solution was 0.500. (a) Denoting the initial, unknown concentration as [Cu2+]i, write an expression for the final concentration, [Cu2+]f, after dilution. Units of concentration are ppm. (b) In a similar manner, write the final concentration of added standard Cu2+, designated as [S]f.

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