# Beers Law Absorbency Lab

## Background Information

Aunt Elda was given a mystery amount of anesthesia (a pain relieving medication, inducing sleep) during her surgery to remove her appendix, unfortunately, information as to whether she lived, died, or woke up during surgery is unknown. Our job was to take the sample of "anesthesia" and compare it to percentages of transmittance of set samples to find out. The concentration levels we tested were from 10% - 60%, under the understanding that anything over 40% would kill her, and we know if it is reading that high after 60%, she was sure gone in no time. Then we also knew that if it was anywhere around 10% she would have woken up during that surgery which would've been just as horrifying.
The beaker above represents the mystery green anesthesia that was used in our experiment

## Mixing the Solutions

For this experiment, we wanted a base line of what each percentage of "anesthesia" would transmit at for concentration level, to compare to Aunt Elda's, so we created each one (10, 20, 30, 40, 50, and 60) with the anesthesia and water. To get the % concentration we wanted, say 10%, we would put exactly 1 mL of the 100% concentrated anesthesia into a graduated cylinder and added 9 mL water. 20%= 2 mL anesthesia, 8 water, etc. each time adding up to 10 mL, Woah, crazy, math, I know.

## Procedure

To do this, you must use a Colorimeter. A Colorimeter monitors the light received by the photocell as either an absorbance or a percent transmittance value. *Key point: a higher concentration of the solution absorbs more light and transmits less than that of a lower concentrated solution.
Colorimeter and cuvettes

1. Connect the Colorimeter to the computer interface.Prepare the computer for data collection by opening the file "11b

Beer's Law" from the Chemistry with Computers folder of Logger Pro.

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 Co lorimeter has a CAL button, Press the < or> button on the Colorimeter to select a wavelength of 635 nm (Red) for this experiment. Press the CAL button until the red LED- begins to flash.. 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. type 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 cuvette as directed by teacher. Enter next solution

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 of the 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.

## Beer's Law Results and Proof

Concentration...... Transmittance...... Absorbance

0............................. 100.539 ..................-0.002

10........................... 86.980...................... 0.061

20........................... 69.121...................... 0.160

30........................... 52.779...................... 0.278

40........................... 37.233...................... 0.429

50........................... 30.545...................... 0.515

60........................... 25.846...................... 0.588

Aunt Elda's: ...........52.744...................... 0.278

This graph shows the line on how much was absorbed per concentration percentage.

## Results

As you can see by the data, the amount of anesthesia she was given was not enough to kill her, and by no means did she wake up in the midst of her surgery; being 40% would kill and 10% was not enough and she had 30% solution. Therefore, she done messed up in her life some other irrelevant way. Beer's Law helped me solve this in the way that you could physically see where solutions ended up and how the mystery one compared to the sample ones. Turned out to be not so mysterious after all.