our depening now me Preceduie coninoe ecrec A yellow dye, FD&C; yellow 3, is use

Question

our depening now me Preceduie coninoe ecrec A yellow dye, FD&C; yellow 3, is used in some candy coatings. A 150 × 10-M solution of this dye has an absorbance of 0.209 at its max. Calculate the molar absorptivity, E, of the dye at this wavelength, assuming a sample cell with a 1.0 cm pathlength. a. b. The yellow dye from one piece of candy is completely extracted into 10.0 mL of water and diluted to 50.0 mL with water. The absorbance of the diluted solution is 0.496 at its . Calculate the molarity of the dye in the diluted solution Calculate the number of grams of this dye in the coating of one piece of candy (MM of dye 271 g/mol). c.

Explanation / Answer

A) A=ecl A = absorbance, e = molar absorptivity, l = path length, c = concentration of solution

e= A/cl = 0.209 / ( 1cm x 1.50*10^-5 M) = 13933.3 M-1 cm-1

B) Using e from part A and c = A/el

c = 0.496 / (1cm x 13933.3 M-1 cm-1) = 3.56 x10^-5 M

C) we need to use the fact that a 50 mL solution of the dye has a concentration of 3.56 x10^-5 M to work out the number of moles present in the coating of one piece of candy.

So n=cxv/1000 = 3.56 x10^-5 M x 50/1000 = 1.78 x10^-6 mol

n= m/M so m = nM = 1.78 x10^-6 mol x 271 g/mol = 4.82 x10^-4 g of yellow dye per piece of candy

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