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button and a dialog box with a series of choices will appear. Scroll down the list and
choose “colorimeter” (NOT “light sensor”), and a picture representing the colorimeter
detector will appear under the “Analog channel A” plug picture.
Calibrating the Pasco system:
We need to calibrate the Pasco system for it to work properly. What this means,
essentially, is telling it what “0” is and what “maximum” is. Double click the picture of
the light sensor that is now below the picture of the “Analog channel A” plug. Physically
set the colorimeter to 0%T on the box. When the current value seems to stabilize (it will
oscillate, but the oscillations should be around the same value), click on the “Read Low
Value” box. This will set the low reading, or 0% Transmittance. Dakota State University page 206 of 232 Experiment 20: Beer’s Law General Chemistry I and II Lab Manual Now, place a cuvette with distilled water in the colorimeter, being sure that the
SMOOTH sides to the cuvette are facing the light path. (HINT! NEVER handle a
cuvette on the smooth sides; you want this to be as clean as possible.) Set the colorimeter
to the correct color. (HINT! Discuss the options with your partners and choose the color
that is most absorbed by the substance. Remember; the color that is absorbed is the color
you do not see in the solution.) When the current value again stabilizes, click on the
“Read High Value” box. This has set the 100% Transmittance reading. Your Pasco
system now knows what the low and high values are, and will automatically calibrate
itself. Close the dialog box.
Setting up the sampling options:
The Pasco system can either operate with automated sampling or manual
sampling. Automated sampling is superb for taking data over time; however, our
solutions will not change over time (hopefully). Therefore, we want to set the Pasco
system for manual sampling.
To do so, click on the “sampling option” button. In the dialog box, choose the
“keyboard” option. Type in “concentration” for parameter, and the correct concentration
units for units (probably % w/v or % weight/volume, because it is so common and
simple; 3% w/v means 3 g of solute for every 100 mL of solvent). Close the dialog box.
Now, click and drag the picture of the table to the picture of the “analog channel
A” box, just as you did when choosing the colorimeter. Choose the “Absorbance”
option. If you would like a second box to use percent transmittance for a comparison,
repeat the procedure. In the table(s), make sure “concentration” is showing by clicking
on the appropriate button on the table (the “add column” button, which has a funny little
picture that’s difficult to describe). Also, click and drag the “digital meter” button, and
whatever additional output you’d like to see.
Collecting the data:
Now you are ready to run the experiment. Click the “record” button to start the
experiment. A dialog box will appear that prompts you to input your first concentration.
Make sure that you ri...
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