How to Find the Concentration of a Solution With Absorbance

How to Find the Concentration of a Solution With Absorbance


Determining the concentration of a solution is a fundamental task in chemistry. There are various methods to achieve this, and one commonly used technique is by measuring the absorbance of the solution. Absorbance refers to the amount of light absorbed by a substance, which can be used to determine the concentration of the solution. This article will guide you through the steps involved in finding the concentration of a solution using absorbance, as well as answer some frequently asked questions about the topic.

Step 1: Prepare the Solution

The first step is to prepare the solution whose concentration you want to determine. Ensure that the solution is properly mixed and homogeneous. It is crucial to have accurate measurements of the solute and solvent used to create the solution.

Step 2: Select the Appropriate Wavelength

Next, you need to choose the appropriate wavelength of light for your analysis. This wavelength should correspond to the absorption maximum of the solute in the solution. The absorption maximum is the wavelength at which the solute absorbs light most efficiently. To determine this, you can consult a database or reference material specific to the solute you are working with.

Step 3: Set-Up the Spectrophotometer

A spectrophotometer is a device used to measure the absorbance of a solution. Set up the spectrophotometer according to the manufacturer’s instructions. Ensure that the wavelength is set to the selected value from Step 2.

Step 4: Calibrate the Spectrophotometer

Before measuring the absorbance of the solution, it is essential to calibrate the spectrophotometer. This involves measuring the absorbance of a blank solution, which contains the solvent but no solute. The absorbance of the blank solution is typically zero. If not, adjust the spectrophotometer settings until a zero absorbance is achieved.

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Step 5: Measure the Absorbance of the Solution

Once the spectrophotometer is calibrated, measure the absorbance of the solution. Place the solution in a cuvette and insert it into the spectrophotometer. Record the absorbance value obtained.

Step 6: Construct a Calibration Curve

To determine the concentration of the solution, you need to create a calibration curve. This curve relates the absorbance values obtained in Step 5 to known concentrations of the solute. Prepare a series of standard solutions with different known concentrations of the solute. Measure the absorbance of each standard solution using the same procedure as in Step 5.

Step 7: Determine the Concentration of the Unknown Solution

Using the calibration curve, determine the concentration of the unknown solution by interpolating the absorbance value obtained in Step 5. Locate the absorbance value on the y-axis of the calibration curve and draw a horizontal line to intersect the concentration axis. The concentration of the unknown solution is the corresponding value on the concentration axis.


Q: What is absorbance?

A: Absorbance is a measure of the amount of light absorbed by a substance. It is represented by the symbol “A” and is related to the concentration of the absorbing species in a solution.

Q: How does absorbance relate to concentration?

A: Absorbance and concentration are directly proportional. As the concentration of a solute increases, the absorbance of the solution also increases. This relationship allows us to determine the concentration of a solution by measuring its absorbance.

Q: Why is it important to calibrate the spectrophotometer?

A: Calibrating the spectrophotometer ensures accurate measurements by accounting for any background absorbance or deviations in the instrument. It allows us to obtain reliable and precise results.

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Q: Can this method be used for all solutes?

A: This method can be used for solutes that exhibit a measurable absorbance at a specific wavelength. Different solutes have different absorption properties, so it is important to select the appropriate wavelength for analysis.

Q: Are there any limitations to this method?

A: This method assumes a linear relationship between absorbance and concentration, which may not hold true for all solutions. Additionally, impurities or interfering substances in the solution can affect the accuracy of the results.


Determining the concentration of a solution using absorbance is a widely used method in chemistry. By following the steps outlined in this article, you can accurately find the concentration of a solution. Remember to select the appropriate wavelength, calibrate the spectrophotometer, measure the absorbance, and construct a calibration curve. With these techniques, you can confidently determine the concentration of unknown solutions and advance your understanding of chemical analysis.

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