# Graphical relationship between absorbance and concentration

### Chem - Experiment II This direct relationship between absorbance and concentration exercise and used to determine the concentration of a dye in a commercial drink. Click the Save Graph to Files button to save your absorbance spectrum. Absorption spectrum. A graph of absorbance vs. wavelength for a hypothetical compound. There is a relationship between concentration and absorbance. How does the solution color relate to its absorbance spectrum? In obtaining an absorbance spectrum, you are getting a graph representation of how light is interacting . it shows a linear relationship between absorbance and concentration.

In Part 3, the same procedure was used as in Part 2 to determine the phosphate concentration in an unknown solution. It also was not diluted because it was a water sample. When only the molybdate binds with phosphate, it turns the solution blue, indicating the presence of PO The linear relationship between absorbance and concentration displays that absorbance depends on the concentration.

To calibrate the spectrometer, a solution containing 5. Since the species of interest was the phosphate, everything but the phosphate was used in the blank, and subtracted from the measured absorbance of cuvette containing a phosphate solution. The results were not quite as expected, since the data was askew due to a great amount of experimental error in Part 1 of the lab.

You would most likely want to choose wavelengths like nm or nm where there is a lot of room for absorbance change. Now for the fun part! Using the calibration plot that YOU made from the data two pages ago. We are going to determing the concentration of an unknown solution.

### Beer's Law Lab Explained: Absorbance vs. Concentration - SchoolWorkHelper

Make sure you have your plot ready, because here we go! Here's a typical problem. You take 3mL of your unknown sample and 7mL water and mix them together. The dilluted sample gives an absorbance of 0.

## Beer’s Law Lab Explained: Absorbance vs. Concentration

The linear-regression statistics for these two lists are displayed for the equation in the form: Record the slope, a, in the data table. One indicator of the quality of your data is the size of b. Obtain about 5 mL of the unknown NiSO4 in another clean, dry, test tube.

Record the number of the unknown in the Data and Calculations table. Wipe the outside of the cuvette, place it into the colorimeter, and close the lid.

### Beer's Law - Theoretical Principles

To find the absorbance of the unknown NiSO4 solution: Press to monitor the colorimeter. The absorbance value of the unknown is displayed on the screen of the TI calculator. When the absorbance reading stabilizes, record its value in Trial 6 of the Data and Calculations table round to the nearest 0. Discard the solutions as directed by your teacher. Proceed directly to Steps 1 and 2 of Processing the Data.

Determine the concentration of the unknown NiSO4 solution. Divide the absorbance value you obtained in Trial 6 by the slope of the regression line.