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Topic: Beer's Law  (Read 4340 times)

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Offline 2clients

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Beer's Law
« on: February 17, 2009, 04:17:43 PM »
A particular dye solution has an absorbance of 0.984 in a 2.0-cm pathlength cuvette. When the same solution is placed in another cuvette, it has an absorbance of 0.652. What is the pathlength of the second cuvette?

I believe this applies to Beer's Law, A = ebc , Where A is absorbance, e molar absorptivity, b pathlength, and c molarity.

Because it is the same solution, I believe I need to find the pathlength that when multiplied by 0.652 results in the product of 0.984*2, or about 3.02 cm.

Any help greatly appreciated.

Offline ARGOS++

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Re: Beer's Law
« Reply #1 on: February 17, 2009, 04:34:01 PM »

Dear 2clients;

You are right to use Beer-Lambert law, but you did a mistake with.

Think about the law and your solution: As you used in both cases the same solution means that e as also c are constant.

Or with other words: In your case A and b are direct proportional!
And that means that your path-length is wrong.

Can you re-calculate the path-length with this help?
Good Luck!
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Offline Borek

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Re: Beer's Law
« Reply #2 on: February 17, 2009, 04:36:47 PM »
Think this way: everything else being identical, if the absorbance is lower, is it possible for the cuvette to be longer?
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Offline 2clients

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Re: Beer's Law
« Reply #3 on: February 17, 2009, 04:49:40 PM »
Thank you Borek and Argos.  I understand it much better now.

I believe the answer is 1.32 cm

Offline ARGOS++

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Re: Beer's Law
« Reply #4 on: February 17, 2009, 04:51:26 PM »

Dear 2clients;

Exact!

You 're welcome!   ─   Soon again.

Good Luck!
                    ARGOS++

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