PRELAB GUIDING QUESTIONS/SIMULATIONS I: You will be collecting data (in your gro

Question

PRELAB GUIDING QUESTIONS/SIMULATIONS I: You will be collecting data (in your group) to determine the relationship between wavelength (lambda, ), concentration, and absorbance. You will use the interaction of light with solutions to determine the concentration of an absorbing species. However, it is important to identify what is doing the absorbing prior to determining the concentration of the absorbing species. Such information can be gathered by collecting absorbance data for a solution at various wavelengt Step 2: Your group will be given two different salt solutions of the exact same concentration. You are to measure the absorbance for each solution at every 20 nanometers from 400-700 nm to generate a spectrum and to determine the best wavelength at which to measure the absorbance of the two solutions. Make sure you use the appropriate spectrophotometer or colorimeter to collect such data. You will be sharing your absorption spectra with the rest of the class to identify what species in solution is actually absorbing light.

Explanation / Answer

It is the Cu2+ ion that is doing the absorption.

At aparticular wave length the absorption is maximum. This is called lambdamax. It is important to meassure the absorbance from 400 - 700 nm to find the lambdamax.

Absorbance = molar absorptivity x path length x concentration

For a given spectrum both path length and concentration are constants.

Hence Absorbance is directly proportional to molar absorptivity.

So just look at the spectrum where the absorption is half the value than that 630 nm, the corresponding wave length has half molar absorptivity than 630 nm.

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