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### Topic: calculation  (Read 5908 times)

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#### abcc

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##### calculation
« on: December 14, 2006, 09:18:40 PM »
calculation question
The transmittance of a solution is found to be 40%. What is the transmittance if the solution is diluted in half?

#### Dolphinsiu

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##### Re: calculation
« Reply #1 on: December 15, 2006, 01:30:21 AM »
http://en.wikipedia.org/wiki/Transmittance

You can find it from above website!

T% = I/Io x 100%

Assume half-diluted solution is passed through by twice as light intensity in original solution,

Then A = - log 2I/Io + log I/Io = log I/2I = log 1/2 = -log T+ logTo = log 40/T

so log 1/2 = log 40/T

T = 80%

#### enahs

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##### Re: calculation
« Reply #2 on: December 15, 2006, 01:39:30 AM »
Go back to your basic Beer-Lambert Law and other formulas relation to transmittance.

A = ? * b * c
and
A= -log (T) -> T= 10-A

T = 10-(? * b * c)

What will happen?

Note, that is T, not %T
« Last Edit: December 15, 2006, 01:45:28 AM by enahs »

#### Dolphinsiu

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##### Re: calculation
« Reply #3 on: December 15, 2006, 01:54:06 AM »
Sorry! I have made a wrong mistake!
The last line should be T% = 80%

#### chiralic

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##### Re: calculation
« Reply #4 on: December 15, 2006, 06:50:13 PM »
To Dolphinsiu:

Could you tell us where come from the mathematical expression
A = - log 2I/Io + log I/Io that you wrote?

If you check a plot %T vs Concentration and Plot Absorbance vs Concentration you'll see that the %T vs C is not linear.

Regards,

Chiralic

#### ARGOS++

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##### Re: calculation
« Reply #5 on: March 24, 2007, 06:19:33 PM »
Dear ALL,

Have most of you already forgotten what Mr A. Beer, Mr. J. H. Lambert, and
Mr. P. Bouguer have told everybody about Light and Matter, ~250 years ago?

The Beer-Lambert-Bouguer Law:
http://www.p-forster.com/english/themes/Spectroscopy/BASICS/Corrected Beer's Law.htm

Good Luck!
ARGOS++

P.S.:  Hint: Half the concentration is "exactly" the same as half the pathlength (Why?).
( "Wiki" is by far NOT all times a/the best Solution! )

« Last Edit: March 25, 2007, 08:38:29 AM by ARGOS++ »