Question

PLEASE HELP!!!! I CANNOT FIGURE THIS OUT FOR THE LIFE OF ME!!!

After isolating the sulfonated product, the filtrate volume is found to be 19.47 mL. A dilution using 1 mL of filtrate and 99 mL of water gives a solution with an absorbance of 0.743. How many moles of indigo carmine were produced? (Molar absorptivity of indigo carmine was found to be 12,100 M-1cm-1)

Answer 1

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Answer 2

Beer-Lambert Law: \(\sf Abs=\epsilon*l*M\)

\(\sf \epsilon\)=molar absorptivity coefficient
\(l\)= path length
\(M\)= Molarity (concentration) ; \(M=\dfrac{n_{solute}}{L_{solution}}\) (where n=moles)


substitute in: \(\sf Abs=\epsilon*l*\dfrac{n_{solute}}{L_{solution}}\)

Answer 3

I realize this is the right equation to use, but do I use the 100mL or the 25.65mL?

Answer 4

first find the concentration in the diluted sample, 1 mL filtrate + 99 mL water =100 mL

once you know the concentration scale that up to the volume produced.

(dont use the extended form of the formula i wrote)

Answer 5

also, do we need to do anything with the cm^-1?

Answer 6

nope, that accounts for cuvette, most cuvettes are 1 cm in length. \(l=1~cm\)

Answer 7

right, I forgot about that. So I put Moles=(.616)(.1L)/(12100M^-1cm^-1) but I still got it wrong.

Answer 8

where did you get 0.616?

Answer 9

sorry, I re-opened the problem, and it gave me a different number than .743

Answer 10

oh true. well by doing that you're only finding the concentration of the diluted sample.

you have to find the concentration of the original sample, use: \(M_1V_1=M_2V_2\)

Use the molarity and the volume to find the moles.

Answer 11

I was thinking that, that we were using the volume of the diluted solution, but didn't think it mattered... THANKS!!!

Answer 12

no problem!

Answer 13

So just to check, I would use the answer from beers law, and then solve for M1=(ANS)(.1L)/(19.47/1000) using the numbers from this problem

Answer 14

yeah, then to get moles multiply the volume and molarity