Tuesday, May 22, 2012

Beer's Law Lab

In this lab, we measured the absorbance of five different concentrations of a solution and used these data to find the unknown concentration of a solution. This was done by using a calorimeter, which directs red light through the solution into a photocell, which measures how much light passed through the solution. The data from the calorimeter were collected and analyzed through Logger Pro.

I created five different solutions of known concentration. The first had a concentration of .08 M, the next, .16 M, third, .24 M, fourth, .32 M, and the fifth, .4 M. After calibrating the calorimeter, I measured the absorbance of each solution and obtained the following results:

From this, we can see that the concentrations followed a relatively consistent line (deviations can be explained by measurement errors). Because the absorbance is linear when compared to concentration, we can use this line to predict the concentration of an unknown substance by measuring its absorbance.

We determined the absorbance of the solutions to be as follows:

Unknown 1: .186
Unknown 2: .551
Unknown 3: .367

By plotting these points on the line of best fit, we can see that the concentrations of each respective substance is approximately:

Unknown 1: .155 M
Unknown 2: .365 M
Unknown 3: .26 M

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