Spectrophotometric Analysis of Permanganate Solutions PLEASE HELP!! A student, f

Question

Spectrophotometric Analysis of Permanganate Solutions

PLEASE HELP!!

A student, following the procedure in this experiment, determined the percent transmittance of two solutions of unknown concentration. The first was 96% and the second was 3%.

(1) Convert the first percent transmittance to an equivalent absorbency. Briefly explain why the student should or should not be confident in reading the concentration of permanganate ion in the unknown directly from the Beer's law plot.
(2) Convert the second percent transmittance to an equivalent absorbency. Briefly explain why the student could not have read this percent transmittance accurately from the absorbance scale on the spectophotometer.
(3) Briefly explain why the student should or should not be confident in reading the concentration of the second unknown directly from the Beer's law plot.
(4) Suggest something the student could do with the second sample that would make the determination of the concentration of permanganate ion more accurate.

Explanation / Answer

1. A = -log(0.96) = 0.0177.

2. A = -log(0.03) = 1.52.

3. Beer's law plots have higher experimental measurement errors (inaccuracies) at very low and very high absorbance (concentration) values.

4. You can dilute the sample (with a known volume of water) so that the absorbance values are of an intermediate value (between 0.1 and 1), and work back from the Beer's law plot to get the original concentration.

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