Much More than Pretty Colors
A sample analysis using a smartphone.Copyright 2022 Usha Devathosh, Rice University RET
In a visible spectrophotometer a beam of light shines into a solution containing the sample and detects how much of it comes out of the other side of the solution. Students can compare the amount of light absorbed by the pure solvent to the amount absorbed when the sample is dissolved in it. Spectrophotometers can report measurements such as absorbance. In this investigation, students are guided to construct a spectrophotometer to discover the relationship between absorbance and concentration and ultimately the concentration of an unknown solution.
Spectroscopy is the study of interaction of light and matter as a function of wavelength. Engineers and scientists use spectroscopy as a tool to analyze constituents in various substances and have a wide range of applications in industries. Engineers and scientists use spectroscopy to determine the impurities, presence, or absence of some components in a mixture, and to find the concentration of specific compounds in a solution. For instance, quality control engineers use the spectroscopic method to find the concentration of various dyes used in sports drinks. The basic principles of spectral analysis that students learn in school can also be applied to the more sophisticated instrumentation required to access the ultraviolet, infrared, and X-ray regions of electromagnetic spectrum.
After this activity, students should be able to:
- Relate the absorbance to and concentration of a solution.
- Construct a simple spectrophotometer.
- Analyze spectroscopic data to find the concentration of a component in a solution.