Determing the Concentration of a Solution: Beer’s Law

INTRODUCTION:

The primary objective of this experiment is to determine the concentration of an unknown copper (II) sulfate solution. You will be using the colorimeter. In this device, red light from the LED light source will pass through the solution and strike a photocell. The CuSO4 solution used in this experiment has a deep blue color. A higher concentration of the colored solution absorbs more light (and transmits less) than a solution of lower concentration. The colorimeter monitors the light received by the photocell as either an absorbance or a percent transmittance value.

You are to prepare five copper (II) sulfate solutions of known concentration (standard solutions). Each is transferred to a small, rectangular cuvette that is placed into the Colorimeter. The amount of light that penetrates the solution and strikes the photocell is used to compute the absorbance of each solution. When a graph of absorbance vs. concentration is plotted for the standard solutions, a direct relationship should result. The direct relationship between absorbance and concentration for a solution is known as Beer’s law.

The concentration of an unknown CuSO4 solution is then determined by measure its absorbance with the colorimeter. By locating the absorbance of the unknown on the vertical axis of the graph, the corresponding concentration can be found on the horizontal axis. The concentration of the unknown can also be found using the slope of the Beer’s law curve.

OBJECTIVES:

In this experiment, you will

* Prepare CuSO4 standard solutions

* Use a colorimeter to measure the absorbance value of each standard solution.

* Find the relationship between absorbance and concentration of a solution

* Use the results of this experiment to determine the unknown concentration of another CuSO4

VARIABLES:

INDEPENDENT VARIABLE: Concentration of Copper (II) Sulfate Solution

DEPENDENT VARIABLE: Absorbency of...