Chemistry lab question! Help please! A student finds a solution of blue dye #2 (

Question

Chemistry lab question! Help please!

A student finds a solution of blue dye #2 (another food dye we are not using in this lab) in a 1.0 cm cuvette has a maximum absorbance of 0.572 at 613 nm. The molar extinction coefficient, E, of blue #2 at the same wavelength is 1.21 * 10^4 M^-1 cm^-1. Calculate the concentration of this solution. The same student as in question 3 brings the blue dye #2 solution to her friend Bob to confirm the results. Bob has a home built spectrophotometer with a special sample cell that is 5.0 cm in length. Will Bob be able to accurately confirm the concentration of the solution preciously determined by the student? Explain. What could Bob do to improve his results?

Explanation / Answer

3)

Use the relation,

Absorbance = molar absorptivity x path length x concentration

..........or, A = epsilon x L x c

Absorbance is unitless , molar absorptivity or molar extinction coefficient is in units M-1cm-1 ,

concentration is in mols / L

Hence , substituting the given values we get,

c = A / epsilon x L

.... = 0.572 / 1.21 x 104 X 1.0

..... = 4.727 x 10-5 M

4. The result would differ due to a different path length of the home built spectrophotometer ised by

.....Bob , and as such it cannot be accurately confirmed. However, the sample , if diluted five times can

.....conform to expected result.

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