# UV-VIS & beer's law calculation

• March 31st, 2008, 08:42 PM
az77
UV-VIS & beer's law calculation
I've been trying to figure this one out for more than a day now, and can't seem to get it:

The UV-VIS absorbance of a solution of 1.000X10^-3 M K2Cr2O7 was 0.020 and 0.005 at 450nm and 530nm, respectively. A solution of 1.000X10^-4 M KMnO4 did not absorb at 450nm, while its absorbance at 530nm was 0.042. The UV-VIS TRANSMITTANCE of a mixture solution of K2Cr2O7 and KMnO4 was measured to be 0.500 and 0.250 at 450nm and 530nm, respectively. There are no other compounds in the solution. Find the concentration of potassium ion (K+) in the mixture. A 0.100cm quartz cuvette was used.

Thank you!
• April 1st, 2008, 04:44 AM
Zitterbewegung
What's the deal? Convert the transmittance to absorption (1-absorption=transmittance) and calculate the concentration of the Dichromate via the 450 nm absorption (Beer's law), you have all the data you need to plug it into the equation. Then calculate the absorption at 530 nm from the Dichromate and you are left with the part from the Permanganate. From this you can easily calculate the concentration of K(+) ions in the solution.
• April 1st, 2008, 09:28 AM
az77
Thank you, I will try working around with the problem. And I already did convert transmittance to absorbance by using: A = -log(T) ... I just seem to get stuck along the way, but thank you again.