You have been sent to investigate for trace amounts of the iodide ion (I^-) in g

Question

You have been sent to investigate for trace 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 I^- into I_2 and mixed with a dye to form a colored complex. a) a. A 3.15 times 10^-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 (lambda_max = 635 nm), which of the following dyes was most likely used to form the colored complex:/Allura Red Brilliant Green Tartrazine (Yellow 5) Not enough information

Explanation / Answer

a)

Apply Beer Law

A = e*l*M

M = 3.15*10^-6 M

A = 0.267

l = 1 cm

for the colored sample:

Correct absorbance

Areal = Asample - Ablank = 0.267-0.019 = 0.248

A = e*l*M

e = A/(l*M) = 0.248/ /(1*3.15*10^-6)

e = 78730.158

b)

A = 0.175

find concentration of I- unkown

apply

A = e*l*M

correct A

A = 0.175-0.019 = 0.156

substitue

M = A/(e*l)

M = (0.156)/(78730.158 *1) =

0.00000198145

M = 1.98*10^-6

c)

based on the WL max:

If the solution absorbs 665 light --> red is absorbed; choose allura red

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