1 1 ) You have been sent to investigate for trac:e amounts of the iodide ion (I)
ID: 593569 • Letter: 1
Question
1 1 ) You have been sent to investigate for trac:e amounts of the iodide ion (I) in groundwater around the GGC campus.
To perform your analysis, 1 .00 L of a groundwater sample is first filtered, then treated to oxidize all the r into lz and
mixed with a dye to form a colore:d complex.
a) A 3.15 x 10E-6 M solution of the colored complex exhibited an absorbance of 0.267 at 635 nm in a 1 .00 cm cuvet.
A blank solution of distilled water had an absorbance of 0.019. Calculate the molar absorptivity of the colored
complex.
b) The analysis of an unknown groundwater sample gave an absorbance of 0.175. Calculate the concentration of I in
the unknown groundwater sample in both molarity (M) and ppm.
c) Based on the wavelength at maximum absorbance (Lamda max= 635 nm), which of the following dyes was most likely used to form the colored complex: (Circle the answer)
Allura Red
Brilliant Green
TaMazine (Yellow 5)
Not enough information
Explanation / Answer
Ground water analysis
a) molar absorptivity of complex = absorbance/concentration x path length
= (0.267 - 0.010)/3.15 x 10^-6 x 1
= 81587.3 M-1.cm-1
b) Unknown sample absorbance = 0.175
Molarity = (0.175 - 0.010)/81587.3
= 2.02 x 10^-6 M
= 2.02 x 10^-6 mol/L x 127 g/mol x 1000
= 0.256 ppm
c) based on absorbance at 635 nm, the dyes forming the complex is,
Brilliant green
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