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CHEM272Exam1KeyS10

# CHEM272Exam1KeyS10 - CHEM272 Exam#1 Answer Key Both...

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CHEM272 Exam #1 Answer Key Both versions Spring 2010 Version #1 (given to 9am lecture section) 1) a) A volumetric pipet is more precise b) The absorbance after 2.5 minutes will be loewr than at 10 minutes since the CBBG-BSA complex hasn’t fully formed yet. 2) A few ways to do this – here is one: B + H 2 O BH + HO K b = [ HO ][ BH ] [ B ] Taking the log of both sides gives: log 10 ( K b ) = log 10 [ HO ][ BH ] [ B ] Λ Ν Μ Ξ Π Ο = log 10 [ HO ] log 10 [ BH ] [ B ] Λ Ν Μ Ξ Π Ο = pOH log 10 [ BH ] [ B ] Λ Ν Μ Ξ Π Ο The first term on the left is the pK b (the negative log of the K b ), so: pK b = pOH log 10 [ BH ] [ B ] Λ Ν Μ Ξ Π Ο Rearranging by moving the log term to the other side gives: pOH = pK b + log 10 [ BH ] [ B ] Λ Ν Μ Ξ Π Ο 3) This problem involves multiplying dimensions to get area and adding areas to get a total area. Remember that for multiplying dimensions, you need to use the fractional variance (relative uncertainty) and multiply by the area to get the absolute uncertainty. For addion, you need to use absolute variances.

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For the first tract on the left, total area = 16 x 13 = 208 miles 2 The uncertainty in this area is: uncerta int y = 208 2 13 Ξ Π Ο 2 + 1 16 Λ Ν Μ Ξ Π Ο 2 = 34.539832 I am including some extra decimal places and will round off at the end. For the second tract of land on the right, total area = 11 x 15 = 165 miles 2 The uncertainty in this area is: uncerta int y = 165 1 11 Ξ Π Ο 2 + 2 15 Λ Ν Μ Ξ Π Ο 2 = 26.627054 The combined area = 208 + 165 = 373 miles 2 The error in the combined areas = (34.539832) 2 + (26.627054) 2 = 43.611925 This error, reported to one sig fig, is 40, so our area is reported as 370. The answer is 370 ± 40 square miles. 4) The portion of CBBG that absorbs the logest wavelength of light is the larges conjugated portion, which is shown in red below: a) The conjugated portion on the lower left is missing. This makes the conjugated system
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CHEM272Exam1KeyS10 - CHEM272 Exam#1 Answer Key Both...

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