Question

The extinction coefficient for FD&C Blue Dye is #1 is 138,500 cm-L/mol at 630nm. A chemist collected the following data at 630 nm. She also found that the absorbance of an FD&C Blue Dye #1 solution of unknown concentration was 0.309. Use your graphing calculator to generate a standard curve from this data set, and use it to determine the concentration of the unknown solution.

Answer 1

Beers law states that Absorbance (A)= e( molar extinction coefficient)*b( path length)*C (concentration)

given e= 138500 cm-L/mole, assuming b= path length =1 cm

A= 0.309

C= A/eb = 0.309/(1*138500)=2.23*10^-6 moles/Liter

when concentration varies A also varies

A = 138500*1*C (1)

C= A/138500 (2)

so a plot of A vs C can be generated ( with out crossing the threshold value of A=2)

assume a value of A raning from 0.1 to 2 ( 0 refer to zero concentration)

Use Eq.2 to calculate A and generate a plot of A vs C.

A	C( concentration, moles/L)
0.1	7.22022E-07
0.2	1.44404E-06
0.4	2.88809E-06
0.6	4.33213E-06
0.8	5.77617E-06
1	7.22022E-06
1.5	1.08303E-05
2	1.44404E-05