Enter the absorbance, path length, and molar absorptivity into the calculator to determine the molarity of a solution. The calculator uses Beer-Lambert law to convert absorbance to molarity.
Absorbance to Molarity Formula
The following formula is used to convert absorbance to molarity:
M = A / (ε * l)
Variables:
- M is the molarity of the solution (M)
- A is the absorbance (unitless)
- ε is the molar absorptivity (L/mol*cm)
- l is the path length (cm)
To convert absorbance to molarity, divide the absorbance by the product of the molar absorptivity and the path length of the cuvette that the solution is in.
What is Absorbance?
Absorbance is a measure of the amount of light absorbed by a solution. It is a unitless quantity that is derived from the logarithm of the ratio of incident to transmitted light through a sample. Absorbance is used in various scientific fields, particularly in spectroscopy, to determine the concentration of solutes in a solution.
How to Calculate Molarity from Absorbance?
The following steps outline how to calculate the molarity from absorbance:
- First, measure the absorbance (A) of the solution using a spectrophotometer.
- Next, determine the path length (l) of the cuvette that the solution is in, typically in centimeters.
- Then, obtain the molar absorptivity (ε) of the solute, which is a constant that depends on the substance and the wavelength of light used.
- Use the formula M = A / (ε * l) to calculate the molarity (M) of the solution.
- After inserting the variables and calculating the result, check your answer with the calculator above.
Example Problem:
Use the following variables as an example problem to test your knowledge.
Absorbance (A) = 0.5 (unitless)
Path Length (l) = 1 cm
Molar Absorptivity (ε) = 100 L/mol*cm
