College Chemistry Lab
posted by L** on .
Suppose that a 2.50x10^6M solution of red dye No. 2 had an absorbance of 0.585 at its wavelength of maximum absorbance. A second solution of red dye No. 2 is too concentrated to read its absorbance so 5.00 mL of the concentrated dye solution was diluted with water to a volume of 150 mL. The diluted solution has an absorbance of 0.289, measured under identical conditions. What is the molarity of dye in the concentrated solution?

For the first one,
Absorbance = kc
A = 0.585, solve for k, c = 2.50 x 10^6M
Use k in the second run of the concd stuff.
A = kc
You will get a concn that must be adjusted because of the dilution. How much was it diluted. From 5 to 150 mL; therefore, the concn will whatever you calculate x the factor 150/5.
Or you can look at it another way. You can say that the absorbance would have been higher than 0.289 by 0.289 x (150/5), then work A = kc the normal way.