What is the Difference Between Calibration Curve Absorbance and Concentration

Concentration, absorbance, and calibration curves are three concepts that help to analyze solutions. In fact, a calibration curve is the graphical representation of the relationship between concentration and absorbance.

What is the difference between calibration curve absorbance and concentration? Concentration is the amount of a substance present in a specific volume of a solution; absorbance is a measurement of how much light a sample absorbs at a particular wavelength. Meanwhile, the calibration curve is a graph that plots absorbance on the y-axis against concentration on the x-axis.

Key Areas Covered

1. What is Concentration
      – Definition, Features
2. What is Absorbance 
      – Definition, Features 
3. What is Calibration Curve 
      – Definition, Features 
4. Relationship Between Calibration Curve Absorbance and Concentration
      – Outline of Common Features
5. Difference Between Calibration Curve Absorbance and Concentration
      – Comparison of Key Differences
6. FAQ: Calibration Curve Absorbance and Concentration
      – Answers to Frequently Asked Questions

Key Terms

Calibration Curve, Absorbance, Concentration

What is Concentration

Concentration is the amount of substance present in a specific volume of a solution. There are different ways to express concentration. Some common units are molarity, parts per million, parts per billion, and percentage. For example, imagine we have 10 grams of salt and dissolve it in 100 milliliters of water. In this case, the concentration of the saltwater solution is 0.1 grams of salt per 1 milliliter of solution.

The equation to calculate the concentration is c= n/v

where c is the concentration of a particular solute, n is the number of moles of solute, and v is the volume of the solution.

Concentration is an essential measurement in the field of chemistry. It is used in preparing solutions, predicting reaction rates, analyzing mixtures, stoichiometry, and understanding colligative properties.

What is Absorbance

Absorbance in chemistry is a concept that deals with how light interacts with a substance. It’s a measure of the amount of light a sample absorbs at a specific wavelength. Absorbance is a unitless quantity, often denoted by the symbol “A”. It’s a ratio between the intensity of light entering a sample (I₀) and the intensity of light exiting (I). A higher absorbance value indicates more light being absorbed.

Absorbance has a relationship with concentration. Generally, the absorbance of a solution increases with the concentration of the colored molecule present. The more colored molecules there are, the more light particles (photons) they can capture and absorb.

Absorbance is measured using spectrometers. These instruments shine light of various wavelengths through a sample and measure the amount of light transmitted or absorbed at each wavelength. This data is then plotted as an absorption spectrum.

There are many applications of absorbance. Some of them include quantitative analysis, monitoring reactions, and biochemistry.

What is Calibration Curve

A calibration curve in chemistry is a graphical tool that determines the unknown concentration of a substance in a sample. It relies on the relationship between absorbance and concentration.

Scientists measure the absorbance of their unknown sample at the same wavelength used for the standards. By referring to the calibration curve, they can find the concentration of the unknown sample that corresponds to its measured absorbance. The curve essentially acts as a reference point for translating absorbance values into concentration values. All in all, absorbance curves are accurate, efficient, and specific.

Relationship Between Calibration Curve Absorbance and Concentration

1. A calibration curve is the graphical representation of the relationship between concentration and absorbance.
2. All three are important in analytical chemistry for determining the unknown concentration of a substance in a sample.

Difference Between Calibration Curve Absorbance and Concentration

Definition

• Concentration denotes the amount of a substance present in a specific volume, while absorbance measures the light absorbed by the analyte in the solution. Meanwhile, a calibration curve is a graphical tool used to translate absorbance values into concentration values.

Units

• Concentration is typically expressed in units like molarity (M), parts per million (ppm), or milligrams per liter (mg/L). However, absorbance is a unitless quantity. The calibration curve has no specific unit, but the axes represent concentration (one axis) and absorbance (the other axis).

Nature

• Concentration is an independent variable, while absorbance is dependent on the concentration of the analyte and other factors like the wavelength of light used and the path length through the solution. Calibration curve is a constructed based on the relationship between absorbance and concentration of known standard solutions.

Conclusion

Concentration, absorbance, and calibration curves are all interrelated concepts used to analyze solutions. Concentration describes the amount of a substance in a solution. Absorbance measures how much light the solution absorbs. A calibration curve is a graph that helps determine an unknown solution’s concentration based on its absorbance. This is the main difference between calibration curve absorbance and concentration.

FAQ: Calibration Curve Absorbance and Concentration

1. What is the relationship between absorbance and concentration?

Concentration and absorbance are directly proportional. This means, higher the concentration, higher the absorbance. Similarly, the lower the concentration, lower the absorbance.

2. What is the use of concentration vs absorbance graph?

A concentration vs. absorbance graph is used to determine the unknown concentration of a solution. It works because absorbance and concentration have a direct relationship, according to Beer’s Law. By plotting known concentrations and their corresponding absorbance values, you create a standard curve.

3. Does high absorbance mean higher concentration?

Yes, the higher the concentration, the higher its absorbance. This is because a  concentration and absorbance of a substance are directly proportional under ideal conditions.

4. Can a concentration be negative?

Concentration can never be negative. This is because the amount of substance cannot take a negative value. Concentration describes how much of something is dissolved or present within another substance.

5. What is the law that states the relationship between concentration and absorbance?

The law that describes the relationship between concentration and absorbance is called Beer’s Law, also sometimes referred to as the Beer-Lambert Law. It states that the absorbance of light by a solution is directly proportional to the concentration of the absorbing substance in the solution and the path length of the light through the solution.

Reference:

1. “Concentration.” Wikipedia. Wikipedia Foundation.
2. “Absorbance.” Wikipedia. Wikipedia Foundation.

Image Courtesy:

1. “Dilution-concentration simple example” By en:User:FirstPrinciples – http://en.wikipedia.org/wiki/Image:Dilution-concentration_simple_example.jpg (Public Domain) via Commons Wikimedia
2. “Calibration Curve” By Kkmurray – Own work (CC BY-SA 3.0) via Commons Wikimedia