How is an indicator different from a dye?

Finding the Concentration of Undiluted Indicator Dye from Solution?

• I am having difficulty determining whether I am following the correct procedures for this problem, any help would be greatly appreciated!! 0.1 mL of an indicator dye solution is diluted by adding 8.9 mL of water. The absorbance of the diluted solution is determined to be 0.561 at 450 nm. The molar extinction coefficient for the indicator dye is 6.0 x 10^3. Given this information what is the millimolar concentration of the undiluted indicator dye solution.

• Answer:

  Beer's law equation says: Absorbance = (molar absorptivity) ( pathlength) (concentration) So, for the diluted solution: 0.561 = 6.0 X 10^3 (1 cm) (C) C = 9.35 X 10^-5 M concentration in the diluted solution To calculate the concentration of the original solution, multiply the concentration by a dilution factor. This is the final volume divided by the initial volume. So, for this case, (9.35 X 10^-5) X (9.0 / 0.1) = 8.42 X 10^-3 M