Kinetics Studies of the Bleaching of Food Dyes >> Step 4: Putting it all together

Kinetics Studies of the Bleaching of Food Dyes

Step 4. Converting absorbance to concentration.

In order to assemble the rate law, Rate = k [dye]^m[bleach]ⁿ, we need to convert the absorbance values to concentrations. To do this, we will use Beer's law, which may be written as:

      abs = ε l [dye]

where l is the path length of light through the solution and ε is the molar absorptivity. For this experiment, we want to know the product, ε * l, since this is the proportionality constant between our measured absorbance and the dye concentration.

To determine the proportionality constant, we will perform a Beer's law calibration by measuring the abs for various dye concentrations. We will then construction a Beer's law plot with abs on the y-axis and concentration on the x-axis. The slope of this line is the porportionality constant, εl. With this proportionality constant, we will be able to determine the concentration for any absorbance value we collected in Steps 1 and 3.

Preparing a set of dilutions of the standard dye

To create a Beer's law plot, we will first prepare a set of dilutions of the standard Yellow 6 dye (using the tutor below) and then run an absorbance measurement of each solution. The dye solution has a concentration of 3.40E-5 M. Complete the following table, which prepares dilutions of the original dye solutions, each with a total volume of 10.00 mL.

Use the simulation below to collect the absorbance vs % dilution data for the Yellow 6 dye solutions.

Use the results of the above simulation to answer the following question:

Please use this information to complete the section of the homework document corresponding to step 4.

This concludes the online tutorial, please be sure to complete the activity form.