Determining if there is a Linear Relationship between Absorbance and Concentration

For this experiment, the goal was finding a relationship between absorbance and concentration. Because Beer's law exists, which says absorbance equals the molar absorptivity times the concentration multiplied by the path length, and molar absorptivity and path length were held constant, the absorbance should have increased linearly with the concentration, hypothetically. To complete the experiment, four solutions were used, cupric sulfate pentahydrate (CuSO4•5H2O), chromic chloride hexahydrate (CrCl3•6H2O), ferric nitrate nonahydrate (Fe(NO3)3•9H2O), and cobaltous chloride hexahydrate (CoCl2•6H2O). For each solution, four molarities were used, 0.1M, 0.08M, 0.06M, and 0.04M, and fifteen samples were taken for each molarity of each solution. A solution was picked to be tested, and the molarities for that solution were then randomly tested. A spectrophotometer was used to measure the absorbance. After the experiment was completed for each solution, the average absorbance value was taken for each molarity, and a linear regression line was completed for these four average absorbance values. Using the linear regression line, a linear regression t test was completed for each solution, and based on the P-value that was obtained, each solution either did or did not support the hypothesis. In the end, the P-value of each solution supported the hypothesis that there is a linear relationship between absorbance and concentration.

Research Done By:

Julie Chang
L'Anse Creuse High School

Andrew Damaske
L'Anse Creuse High School