Question

I need to use Beer's Law to determine a concentration, yet my book states "The Beer-Lambert Law is: A = ε0 b c The terms ε0 (extinction coefficient) and b (path length) are constant under the conditions of this experiment, allowing the further simplification Absorbance α (is directly proportional to) concentration."

Would this not then mean that my number for absorbance is always equal to the number of concentration? I know I need to use y = mx + b, yet my graph is not absorbance x concentration. Instead, absorbance is on the y axis, and time is on the x axis. For reference, my trendline equation is y = -0.121x + 0.353.

Essentially, I need to be able to determine a concentration after a certain amount of time if given the concentration at time zero. Please explain or even include an example as I am really trying to understand. Thank you!!

Answer 1

convert your absorbance-time graph to a concentration-time graph.

For this you will need some standered solutions of known concentrations of coloured compound which is there in our reaction (whose absorbance are we finding out). This will provide us a standered curve of absorbance vs concentration

now we will use this standered curve to find out concentration of experimental solution by putting its absorbance in standered curve.

Thus knowing the absorbance at any time we can find concentration at that time also . Now you can plot concentration vs time plote.