Ch4 Lec 8

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Dilution Worksheets

The following worksheets were originally planned as a pre-lab activity...i did not reformat them for these "lecture notes."

Please complete these worksheets --> Concentration, Molarity, and Dilutions worksheets

Dilution Activity

A lab was originally planned but is now being used as a class activity. In this activity/lab, you were going to determine the concentration of the blue dye found in a "blue" PowerAde sports drink. Although the many details associated with the lab are outlined in the Molarity Lab, the basic take home message is...if you make a set of 3 solutions/dilutions of the blue dye and you use a spectrophotometer to measure how much light is absorbed by the solution (aka, the "absorbance") then you can generate a set of data to complete the following table:

If the [blue dye solution 1] = 0.01 M, [blue dye solution 2] = 0.02 M, [blue dye solution ] = 0.03 M (these are referred to as your "standards"), and solution 1 absorbance is 0.2, solution 2 absorbance is 0.4, solution 3 absorbance is 0.6, AND the sports drink absorbance is 0.5, then you can process this data as described below to determine the concentration of the blue dye in the sports drink.

Processing this Data

1) Write in your notes the above completed table.

2) Go to Excel (or by hand) and make a graph of concentration (x-axis) vs. Absorbance (y-axis) for the standards...do not include the sports drink absorbance in this plot.

- fit a trendline to the data, showing the equation on the graph, note the equation in your notes.

Your trendline equation is in the form of y= m*x + b, or Abs = m*Concentration + b, where b should be 0., there for Abs = m*Concentration. The value for m (or the slope) is the conversion factor between the absorbance and concentration. NOW...plug in the absorbance for the sports drink into your trendline equation and then solve for the concentration:

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