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Quantitative Chemical Analysis | 8th Edition | ISBN: 9781429218153 | Authors: Daniel C. Harris
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Cd2 was used as an internal standard in the analysis of Pb2 by square wave polarography

Chapter 16, Problem 16-F

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QUESTION:

Cd2 was used as an internal standard in the analysis of Pb2 by square wave polarography. Cd2 gives a reduction wave at 0.60 ( 0.02) V and Pb2 gives a reduction wave at 0.40 ( 0.02) V. It was first verified that the ratio of peak heights is proportional to the ratio of concentrations over the whole range employed in the experiment. Here are results for known and unknown mixtures. Analyte Concentration (M) Current (A) Known Cd2 3.23 ( 0.01) 105 1.64 ( 0.03) Pb2 4.18 ( 0.01) 105 1.58 ( 0.03) Unknown Internal Standard Cd2 ? 2.00 ( 0.03) Pb2 ? 3.00 ( 0.03) The unknown mixture was prepared by mixing 25.00 ( 0.05) mL of unknown (containing only Pb2) plus 10.00 ( 0.05) mL of 3.23 ( 0.01) 104 M Cd2 and diluting to 50.00 ( 0.05) mL. (a) Disregarding uncertainties, find [Pb2] in the undiluted unknown. (b) Find the absolute uncertainty for the answer to part (a). 16-

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QUESTION:

Cd2 was used as an internal standard in the analysis of Pb2 by square wave polarography. Cd2 gives a reduction wave at 0.60 ( 0.02) V and Pb2 gives a reduction wave at 0.40 ( 0.02) V. It was first verified that the ratio of peak heights is proportional to the ratio of concentrations over the whole range employed in the experiment. Here are results for known and unknown mixtures. Analyte Concentration (M) Current (A) Known Cd2 3.23 ( 0.01) 105 1.64 ( 0.03) Pb2 4.18 ( 0.01) 105 1.58 ( 0.03) Unknown Internal Standard Cd2 ? 2.00 ( 0.03) Pb2 ? 3.00 ( 0.03) The unknown mixture was prepared by mixing 25.00 ( 0.05) mL of unknown (containing only Pb2) plus 10.00 ( 0.05) mL of 3.23 ( 0.01) 104 M Cd2 and diluting to 50.00 ( 0.05) mL. (a) Disregarding uncertainties, find [Pb2] in the undiluted unknown. (b) Find the absolute uncertainty for the answer to part (a). 16-

ANSWER:

Step 1 of 3

Given that:

 gives a reduction wave at -0.60  V

And  gives a reduction wave at -0.40  V

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