How Can We Measure Solution Concentrations

Absorbance (A) measures how much light is absorbed by the solution and is defined as the negative logaritlim of transmittance. 

Plotting absorbance as a function of wavelength gives an absorption spectrum. The absorption spectrum, that is, the characteristic absorption over a range of wavelengths, can serve as a sort of fingerprint for the identification of a compound in solution. 

The quantitative relationship between absorbance and a solution s concentration is called the Beer-Lambert law and is expressed as 

Sample Problem 4.12 shows how visible spectrophotometry is used to determine the concentration of a colored solution. 

Absorbance values for five standard KMn04 solutions were determined at a wavelength of 528 nm. The data are tabulated here. 

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