by: Haley Kindvall
What to Know
The purpose of this lab is to know whether or not Aunt Elda died due to getting too much anesthesia during her procedure.
Gather these materials before starting: graduated cylinder, computer, food coloring, water, pipet, cuvette, colorimeter, Lab Pro Software
What to Use
The Colorimeter monitors the light received by the photocell as either an absorbance or a percent transmittance. A higher concentration of the solution absorbs more light (and transmits less) than a solution of lower concentration (that transmits more).
1. Connect the Colorimeter to the computer interface. Prepare the computer for data collection by opening the file.
2. You are now ready to calibrate the Colorimeter. Prepare a blank by filling a cuvette 3/4 full with distilled water.To correctly use a Colorimeter cuvette, remember:
• All cuvettes should be wiped clean and dry on the outside with a tissue.
• Handle cuvettes only by the top edge of the ribbed sides.
• All solutions should be free of bubbles.
• Always position the cuvette with its reference mark facing toward the white reference mark at the top of the cuvette slot on the Colorimeter.
3.Calibrate the Colorimeter.
a. Open the Colorimeter lid.
b. Holding the cuvette by the upper edges, place it in the cuvette slot of the Colorimeter. Close the lid.
c. lf your Colorimeter has a CAL button, Press the < or> button on the Colorimeter to select a wavelength flasli. Then release the CAL button.
When the LED stops flashing, the calibration is complete. Proceed directly to Step 7. If your Colorimeter does not have a CAL button, continue with this step to calibrate your Colorimeter.
4. You are now ready to collect absorbance data for the standard solutions. Click “collect”
Empty the water from the cuvette. Rinse the cuvette twice with -1 mL water and then fill it 3/4 full with the first sample of 20%. Wipe the outside with a tissue and place it in the Colorimeter. After closing the lid, wait for the absorbance value displayed on
the monitor to stabilize. Then click keep Itype 20% in the edit box, and press the ENTER key. The data pair you
just collected should now be plotted on the graph. •
5. Discard the cuvette contents as directed by your teacher. Fill the cuvette 314 full with 40% sample. Wipe the outside, place it in the Colorimeter, and close the lid. When the absorbance value stabilizes, click I Keep I, type 40% in the
edit box, and press the ENTER key.
6. Repeat the steps until you have sampled all of the solutions. When you have finished press stop
7. In your Data and Calculations table, record the absorbance and concentration data pairs that are displayed in the table.
8. Examine the graph of absorbance vs. concentration.To see if the curve represents a direct relationship between these two variables, click the Linear Fit button,. A best.fit linear regression line will be shown for your five data points. This line should pass near or through the data points and the origin ofthe graph.(Note: Another option is to choose Curve Fit from the Analyze menu, and then select Proportional. The Proportional fit has a y·intercept value equal to 0; therefore, this regression line will always pass through the origin of the graph).
9. Rinse your Cuvette with water well and dry it the best that you can. Fill full with the unknown solution. Wipe the outside of the cuvette, place it into the Colorimeter, and close the lid. Read the absorbance value displayed in the
meter.(Important: The reading in the meter is live, so it is not necessary to click “collect” to read the absorbance
value.) When the displayed absorbance value stabilizes, record its value in the Data and Calculations table.
10. Discard the solutions down the sink. Proceed directly to Steps 1 and 2 of Processing the Data.
Transmittance: If no light is absorbed, the absorbance is zero (100% transmittance). Each unit in absorbance corresponds with an order of magnitude in the fraction of light transmitted. For A = 1, 10% of the light is transmitted (T =0.10) and 90% is absorbed by the sample.
Absorbance: Absorbance Spectrum. The extent to which a sample absorbs light depends strongly upon the wavelength of light. For this reason, spectrophotometry is performed using monochromatic light. Monochromatic light is light in which all photons have the same wavelength.
RIP AUNT ELDA
Beer's Law Definition: https://www.google.com/#q=beers+law+definition
Concentration Definition: https://www.google.com/#q=concentration+definition+chemistry
Transmittance Definition: https://www.google.com/#q=transmittance+definition+chemistry
Absorbance Definition: https://www.google.com/#q=absorbance+definition+chemistry