Beers Law with a iPad

This Experiment is based on the Chemistry with Vernier Lab book  Experiment 11.

Dan’s Note

This has been adapted to be used at Exhibition’s where using Chemicals causes issues with Risk assessments.  Our solution are made with off the shelf Food colouring, making the solution’s safe and affordable. I would call this a Kitchen Datalogging Experiment.

We have tried it with Red a blue food colouring and works very well. Possible extensions to this could be to look at different brands of food colouring, different colours to see if they all work the same.

Brief

The primary objective of this experiment is to determine the concentration of an unknown coloured solution. To accomplish this, you will use a Vernier Go Direct Colorimeter, it is also possible to use a Vernier Colorimeter or a Spectrometer. The Colorimeter will pass light through the solution, striking a detector on the opposite side. The wavelength of light used should be one that is absorbed by the solution. The red food colouring solution used in this experiment has a deep red color, so Colorimeter users will be instructed to use the blue LED(470 nm). Spectrometer users will determine an appropriate wavelength based on the absorbance spectrum of the solution. The light striking the detector is reported as absorbance or percent transmittance. A higher concentration of the colored solution absorbs more light (and transmits less) than a solution of lower concentration.

You are to prepare five coloured solutions of known concentration (standard solutions). Each is transferred to a small, rectangular cuvette that is placed into the Colorimeter or Spectrometer. The amount of light that penetrates the solution and strikes the detector is used to compute the absorbance of each solution. When a graph of absorbance vs. concentration is plotted for the standard solutions, a direct relationship should result. The direct relationship between absorbance and concentration for a solution is known as Beer’s law.

The concentration of an unknown  solution is then determined by measuring its absorbance. By locating the absorbance of the unknown on the vertical axis of the graph, the corresponding concentration can be found on the horizontal axis. The concentration of the unknown can also be found using the slope of the Beer’s law curve.

Objectives

In this experiment, you will

• Measure the absorbance value of each standard solution
• Find the relationship between absorbance and concentration of a solution
• Use the results of this experiment to determine the unknown concentration of another solution.

Sensors and Equipment

Additional Requirements

You may also need an interface and software for data collection.