5. -8 points HarrisChem7 18.P.18. My Notes You have been sent to India to invest

Question

5. -8 points HarrisChem7 18.P.18. My Notes You have been sent to India to investigate the occurrence of goiter disease attributed to iodine deficiency. As part of your investigation, you must make field measurements of traces of iodine( in groundwater. The procedure is to oxidize(to I2 and convert the 12 into an intensely colored complex with the dye brilliant green in the organic solvent toluene (a) A 2.67 x 10-6 M solution of the colored complex exhibited an absorbance of 0.277 at 635 nm in a 1.000 cm cuvet. A blank solution made from distilled water in place of groundwater had an absorbaof 0.019. Find the molar absorptivity of the colored complex. M1cm (b) The absorbance of an unknown solution prepared from groundwater was 0.139. Find the concentration of the unknown.

Explanation / Answer

absorbance of colored complex= absorbance - absorbance of blank = 0.277-0.019 =0.258

since Absorbance (A)= ebC, b= path length =1cm, C =concentration = 2.67*10-6M,

e= molar absorptivity, =A/eb= 0.258/(1*2.67*10-6)=96629.2/M.cm

for the case of unknwon solution, the absorbance=0.139-0.019= 0.12

since A= ebC, C= A/eb= 0.12/(96629.2*1)= 1.24186*10-6M

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