Adjust solution concentration and watch the cuvette darken in real time as A = εbc is applied.
The Beer-Lambert law is the quantitative foundation of nearly all spectrophotometric analysis, letting chemists determine an unknown concentration from nothing more than how much light a colored solution absorbs — a core analytical technique in AP Chemistry Unit 3 and IChO analytical chemistry.
The law states A = εbc, where A is absorbance (unitless), ε is the molar absorptivity or extinction coefficient (a constant specific to the substance and wavelength used, in L/mol·cm), b is the path length light travels through the solution (in cm, typically 1 cm for a standard cuvette), and c is molar concentration. Because absorbance is directly proportional to concentration, doubling concentration doubles absorbance — a linear relationship that makes calibration straightforward.
Absorbance and transmittance are related but different quantities: transmittance T is the fraction of light that passes through the sample unabsorbed, while A = -log(T), or equivalently T = 10^(-A). This logarithmic relationship means absorbance, not transmittance, is the quantity that scales linearly with concentration — which is why spectrophotometers report and chemists work with absorbance for quantitative analysis.
Building a calibration curve is the standard workflow: prepare several solutions of known concentration, measure each one's absorbance, and plot absorbance versus concentration — the result should be a straight line through (or near) the origin, with slope equal to εb. Once this line exists, measuring the absorbance of an unknown sample and reading its concentration off the calibration curve (or calculating it from the line's equation) gives a fast, accurate concentration determination without needing to know ε independently.
Path length matters directly and linearly: doubling the cuvette path length doubles absorbance at the same concentration, which is why standardized 1 cm cuvettes are used — comparing absorbance values measured at different path lengths without correcting for b produces meaningless results.
This lab lets you adjust concentration and watch the simulated cuvette visually darken as absorbance increases in real time, build a calibration curve from several data points, and solve for an unknown sample's concentration — the complete Beer-Lambert analytical workflow in one interactive tool.