Beer's Law Lab: Absorbance & Concentration Community
Questions, answers and tips from people who use the Beer's Law Lab: Absorbance & Concentration. Shine light through a colored solution and see how absorbance depends on concentration, width and wavelength..
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From the tool guide: common questions about Beer's Law Lab: Absorbance & Concentration
The items below are not posts by community members. They come from the written guide for this tool and are here to get a conversation started. Use “Ask a follow-up” to open a thread about any of them.
What is absorbance?
A measure of how much light a sample absorbs. Each unit of absorbance cuts the light by a factor of ten.
From the tool guide Ask a follow-upWhy do labs choose the peak wavelength?
At the wavelength where the solute absorbs most, small changes in concentration give the biggest change in the reading.
From the tool guide Ask a follow-upKey ideas
- Absorbance A = ε × width × concentration.
- Doubling the concentration or the width doubles the absorbance.
- Transmittance T = 10 to the power of minus A, so the light dims exponentially.
- A solution absorbs the wavelengths that are the opposite color to what you see.
Things to try
- Find the wavelength with the highest absorbance for each solute.
- Double the concentration and check the absorbance doubles.
- Make the cuvette three times wider and compare.
- Read off the concentration that gives 50 percent transmittance.
Where this is used
Hospitals measure hemoglobin and glucose, water labs test pollutants, and chemists find unknown concentrations with spectrophotometers using this law.
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