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Chemistry Forums for Students => Analytical Chemistry Forum => Topic started by: abcc on December 14, 2006, 09:18:40 PM

Title: calculation
Post by: abcc 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? ???

Title: Re: calculation
Post by: Dolphinsiu 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%

Title: Re: calculation
Post by: enahs 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

Title: Re: calculation
Post by: Dolphinsiu on December 15, 2006, 01:54:06 AM

Sorry! I have made a wrong mistake!
The last line should be T% = 80%

Title: Re: calculation
Post by: chiralic 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

Title: Re: calculation
Post by: ARGOS++ 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  (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! )