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Topic: Concentration from absorbance  (Read 25994 times)

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Offline elliotyang

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Concentration from absorbance
« on: January 31, 2009, 08:39:35 AM »
Anyway, i know how to solve this question.
But i got a new problem.

Fish liver oil is an excellent animal source of vitamin A, which concentration is measure spectrophotochemically at a wave length of 329nm.

when 0.1232g of fish liver oil is dissolved in 500mL of solvent, the absorbance is o.724 units. When 1.67*10-3g of vitamin A is dissolved in 250mL of solvent, the absorbance is 1.018 units. calculate the vitamin A concentration in the fish liver oil.

Split like Arkon suggested --Macman104
« Last Edit: January 31, 2009, 11:46:46 AM by macman104 »

Offline Arkcon

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Re: Question regards ionization energies
« Reply #1 on: January 31, 2009, 11:39:37 AM »
You probably should have started a new thread, with a new question, so this forum remains easily searchable for the next person with a similar question.  But anyway ...

You've been given two O.D. readings, and (in a roundabout way) two concentrations of active.  Can you reconcile them, and find an answer?
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline ARGOS++

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Re: Concentration from absorbance
« Reply #2 on: January 31, 2009, 07:01:44 PM »
Dear elliotyang;

Use twice the Beer-Lambert Law:
Absorbance   =   Epsilon * Concentration * Path-Length
(You may also search for the Law.)

Good Luck!
                    ARGOS++


Offline elliotyang

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Re: Concentration from absorbance
« Reply #3 on: January 31, 2009, 07:54:39 PM »

Offline ARGOS++

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Re: Concentration from absorbance
« Reply #4 on: January 31, 2009, 08:08:43 PM »

Dear elliotyang;

In the kind the question is given to you it's implied that no condition should be violated.

Absorption measurements are done in a so called Cuvette, and such a thing has a path-length.
But it is also implied, that the measurements are done in the same Cuvette and so it's allowed to set its value to 1.0 cm

In the first equation where you know the concentration and the absorbance you solve the equation for the Epsilon and insert its value in the second equation, which you can solve for the concentration.

For more information on Beer-Lambert law you may visit:


I hope to have been of help to you.
Good Luck!
                    ARGOS++


Offline Arkcon

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Re: Concentration from absorbance
« Reply #5 on: January 31, 2009, 08:58:42 PM »
Yeah, lets assume that the conditions raised in that block of text you copied from your text book are all satisfied.  If you feel like it, paste it in you answer, if you expect your teacher is trying to trick you.  Can you break your given question into what you know, and what you don't?  Can you plug into the Beer's Law equation, likely found in your text, nearby your quoted block of text, or on ARGOS++:'s website?  And can you work backward from what you know, to what you need to know?
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

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