Beer Law

Introduction:

A useful Analytical tool for determining the concentration of colored material in solution is absorption spectrophotometry. Colored substances absorb light in the visible spectrum and the amount of light absorbed is proportional to the concentration of the substance in solution.

The primary object of this experiment is to determine the concentration of an unknown CuSO₄ solution. In order to do so, first determine the relationship between concentration of the solution and how much light it absorbs. Using a colorimeter which passes light through samples and measures how much strikes a photocell at the opposite end, measure the absorbance of light transmitted through samples of solutions.

Purpose:

The purpose of the lab was to determine the concentration of an unknown solution based on absorbance. To calculate the unknown solution's molarity, one must graph various known measurements of molarity versus absorbance of the CuSO₄ solution.

Materials:

 2-25mL volumetric flasks

 Spectrophotometer 20

 Cuvettes

 Distilled water

 Pipettes

 CuSO₄

Procedure:

1. Label 4-25mL volumetric flasks with 0.1M, 0.2M, 0.3M, and 0.4M

2. Pipette 5mL of 0.5M solution into 0.1M flask and dilute to the mark, mix.

3. Pipette 10mL of 0.5M solution into 0.2M flask and dilute to the mark, mix.

4. Pipette 15mL of 0.5M solution into 0.3M flask and dilute to the mark, mix.

5. Pipette 20mL of 0.5M solution into 0.4M flask and dilute to the mark, mix.

6. The spec-20 should read the transmittance of 0 when empty because none of the light is allowed to pass through. Use LEFT knob so it reads 0 with an empty chamber.

7. Make a "blank" by filling a cuvette (small test tube) about ¾ full of distilled water. Be sure to wipe off finger prints with a Kimwipe, hold the cuvette by the rim, and place it into the spec-20 with the label facing you. Use the RIGHT knob so it reads a transmittance of 100. DI water is clear and all of the light should transmit through

8. Fill another cuvette about ¾ full with the 0.1M solution.