# How Do You Plot a Beer's Law Graph?

To plot a Beer's Law graph, calculate the absorbance and concentration of the radiation being measured. Mark these on the graph, and draw a line corresponding to the standard plot points.

1. Measure the absorbance

Shine a light through the sample. Calculate the transmittance percentage of the sample by multiplying the intensity of the light source by the light transmitted through the sample. Divide 100 by this number, and then multiply the result by log.

2. Measure the concentration

Find the analytical wavelength of the sample. Take samples of the substance's known concentration, and calibrate the spectrophotometer. Find the absorbance of these known concentrations using the analytical wavelength of the sample.

3. Plot the absorbance and concentration

Write all of the absorbance measurements next to their corresponding concentrations in a chart. Make the absorbance values a function of the concentration values. Create a graph that measures the absorbance on the Y-axis and measures the concentration on the X-axis.

4. Plot the data

Label the Y-axis in increments that match the collected absorbance data. Repeat this on the X-axis for the concentration data. Move up the Y-axis based on the first set of absorbance data. Move to the right across the X-axis to the corresponding concentration number. Mark this point with a dot. Repeat this for the entire data set.

5. Create the line

Draw a straight line that goes through as many plot points as possible.

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