Chemical Forums

Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: integral0 on April 01, 2005, 01:15:56 PM

Title: Absorbances
Post by: integral0 on April 01, 2005, 01:15:56 PM
7. The absorbances at a particular wavelength of a set of known concentration solutions was measured on a spectronic 20.  A plot of concentration vs. absorbance gave a slope of 2.100 x 10-4 and an intercept of approximately zero.  What is the value of the molar extinction coefficient (molar absorbivity, E) at the wavelength?
a. 2.128 x 10-4
b. 6120
c. 2.100x10-4
d. 4762
e. 4700

The answer is "a"

I have no clue how to solve it.... ???
Title: Re:Absorbances
Post by: eugenedakin on April 18, 2005, 09:47:42 AM
Hello Integral0,

It appears that there is insufficient information to derive a reasonable conclusion.  Here are a  few questions that I have:
1) What is the intercept if it is approximately zero (is an actual value provided?)
2) What are the molar concentration measured?

The reason why I ask these questions are:

1) given: A/E= molar concentration, if the molar concentration is 1.0 at the given absorbance, then the calculated value is 2.100x10-4.  If you are given a different molar concentration, then this would change the value.
2) if the intercept is not zero, this will change the slope value (it could explain the difference between 2.128x10-4 and 2.100x10-4)

I hope this helps,

Eugene Dakin Ph.D., P.Chem.