Beer's Law Experiment

Introduction

The purpose of this experiment is to obtain an understanding Beer’s Law through experimentation. Beer’s Law states that the absorption of light by a solution changes exponentially with the concentration. In this experiment the equilibrium constant of methyl red was analyzed. This was accomplished by making basic and acidic solutions, then measuring the absorptivity through the spectrophotometer through wavelengths of 430 and 525nm. Then two solutions with both acids and bases added to a solution of methyl red and deionized water were made. Comparing the absorptivity of the acid, base, and solutions, the average equilibrium constant could be measured. Beer’s law is important in the designing of solar panels. Knowing that the absorptivity changes with concentration while everything remains constant is very valuable.

Procedure

First safety glasses were put on, and Microlab program was opened for measuring absorptivity. Then four solutions were very carefully made. Four of the largest beakers were cleaned and wiped dry and labeled, acid, base, solution 1, and solution 2. Each solution contained 10mL of methyl red. The acidic solution also had 10mL of 0.1M HCl and 80mL of deionized water. The basic solution also had 25mL of 0.1M sodium acetate and enough deionized water to make 100mL. Solution 1 also had 25 of 0.1M of sodium acetate, 25mL of 0.1M HCl, and enough deionized water to make 100mL. Solution 2 also had 25 of 0.1M of sodium acetate, 10mL of 0.1M HCl, and enough deionized water to make 100mL.

Each solution was measured in the spectrophotometer for absorptivity at wavelengths of 525 and 430 nanometers and recorded. Careful not to overfill the clear cuvette, so it was only filled three quarters full of solution. Then the pH probe was calibrated using known buffer solutions of 4.0, 10.0, and 7.0. The pH of the two solutions were then taken and recorded. From these values the average pH of methyl red could be calculated.

Data Analysis

Below in table 1and