# Spectrophotometer lab the relationship between concentration and absorbance

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

In visible spectrophotometry, the absorption or the transmission of a is a linear relationship between the absorbance and the concentration of. using this wavelength, solutions of varied concentrations are blue should yield a linear relationship, as the absorbance of a To begin the experiment, the spec spectrophotometer was turned on to allow time for it warm. Experiment II - Solution Color, Absorbance, and Beer's Law How can you determine the concentration of an unknown sample? The difference is that the cation has a DIFFERENT charge, which changes the electron To do this you will use the spectrophotometer to select a wavelength of light and measure and record.

### Chem - Experiment II

Visible spectrophotometers, in practice, use a prism to narrow down a certain range of wavelength to filter out other wavelengths so that the particular beam of light is passed through a solution sample. Devices and mechanism Figure 1 illustrates the basic structure of spectrophotometers. Detailed mechanism is described below. First a collimator lens transmits a straight beam of light photons that passes through a monochromator prism to split it into several component wavelengths spectrum.

A single wavelenth spectrophotometer You need a spectrometer to produce a variety of wavelengths because different compounds absorb best at different wavelengths.

For example, p-nitrophenol acid form has the maximum absorbance at approximately nm and p-nitrophenolate basic form absorb best at nm, as shown in Figure 3. An isosbestic point is the wavelength in which the absorbance of two or more species are the same.

• Spectrophotometry

The appearance of an isosbestic point in a reaction demonstrates that an intermediate is NOT required to form a product from a reactant. An example of isosbestic point Referring back to Figure 1 and Figure 5the amount of photons that goes through the cuvette and into the detector is dependent on the length of the cuvette and the concentration of the sample.

Once you know the intensity of light after it passes through the cuvette, you can relate it to transmittance T. Transmittance is the fraction of light that passes through the sample. This can be calculated using the equation: Transmittance is related to absorption by the expression: With the amount of absorbance known from the above equation, you can determine the unknown concentration of the sample by using Beer-Lambert Law.

Transmittance illustrated by Heesung Shim Beer-Lambert Law Beer-Lambert Law also known as Beer's Law states that there is a linear relationship between the absorbance and the concentration of a sample.

Beer's Law Laboratory

For this reason, Beer's Law can only be applied when there is a linear relationship. 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. This error occurred from not adding the correct amount of solutions to each beaker, throwing off the absorption rate and then the calibration curve. The absorbances of each of the five solutions being wrong also affected the linear equation obtained in Part 1, which made R2 not be as close to the expected value of 1. The linear equation being not a perfect straight line also affected the determination of concentration of phosphate in the Cola in Part 2.

The impact of this experimental error in Part 1 affected the rest of the lab, not allowing for perfect results.

In this experiment, a calibration curve was created by plotting absorbance vs.