Question

Pre-lab: Concentration of Riboflavin 1. The following absorbance spectrum is recorded for a dye. Which is the most likely color of this dye? a. Blue-green b. Colorless c. Red d. Black M stock solution is diluted to 10.00 ml, what is the final 2. If 4.00 mL of a 5.00 x 10 concentration? 3. The absorbance of known concentrations of red food dye were measured in order to generate the following calibration curve. 2. Annotate the graph with the labels and units of the x and y axes. Also add an appropriate title. b. Imagine a red food dye solution of unknown concentration was found to have an absorbance of 0.80. Using the calibration curve, estimate the concentration of the unknown dye solution. ES E-2 193

Answer 1

Answer 1

Correct answer is a) Blue green.

Reason: Maximum absorption by the dye is shown at 625 nm.

So, it means color complementary to this wavelength will be visible. This means dye is of blue-green color.

Answer 2

Stock concentration = 5.00 x 10^-5 M

Volume of stock = 4.00 ml

Volume of dilution = 10.00 ml

Concentration of dilution = (5.00 x 10^-5 M)* 4 ml/10 ml

= 2.00 x 10^-5 M

Final concentration = 2.00 x 10^-5 M

Answer 3

Standard curve is always plotted with absorbance on x-axis and concentration on y-axis.

So, x-axis = Absorbance, unit = unit less

y-axis = Concentration of dye, unit = mol/L

Title: Standard curve of red food dye.

b) Absorbance = 0.80

The graph cuts 0.80 at concentration of 9.00E-3.

So, concentration of red dye = 9.00 x 10^-3 M