Concentration of a Solution: Beer’s Law
The objective of this experiment is to determine the concentration of an unknown copper 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. A higher concentration of the coloured 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 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, as shown. 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 measuring 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.
Add about 30 mL of 0.10 M CuSO4 stock solution to a 100 mL beaker. Add about 30 mL of distilled water to another 100 mL beaker.
Label four clean, dry, test tubes 1-4 (the fifth solution is the beaker of 0.10 M CuSO4). Pipet 2, 4, 6, and 8 mL of 0.10 M CuSO4 solution into Test Tubes 1-4, respectively. With a second pipet, deliver 8, 6, 4, and 2 mL of distilled water into Test Tubes 1-4, respectively. Thoroughly mix each solution by inverting with a stopper. Clean and dry the stirring rod between stirrings. Keep the remaining...
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