PASCO PS-2121 Colorimeter - Manual (Page 2)

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C o l o r i m e t e r PS- 2121
2
unplug the sensor and reconnect it, the sensor retains the last cal-
ibration.
1. Fill a cuvette with distilled water (or other solvent represent-
ing a concentration of zero) and screw on the lid. See “Sam-
ple Preparation” below.
2. Put the cuvette in the Colorimeter and close the lid.
3. Press the Calibration button on the sensor. A light in the
button illuminates to indicate that calibration is in progress.
4. Wait for the light to turn off and then remove the sample.
After calibration, the transmittance of the calibration sample
should read 100% for all colors.
Sample Preparation
1. Fill the cuvette with at least 6 ml of sample.
2. Screw the cap on securely.
3. Handle the cuvette by the cap and wipe the glass clean with a
non-abrasive tissue. Avoid touching the glass.
4. Gently rock the cuvette to distribute the solute molecules
equally throughout the solution. Do not shake the cuvette or
allow air bubbles to enter the solution.
Orienting the Cuvette
To minimize reading variance due to differences or imperfections
in the glass of the cuvette, do the following for each cuvette you
plan to use.
1. Put a cuvette containing distilled water or other solution into
the Colorimeter. Keep the lid of the Colorimeter open.
2. Put a piece of black cloth over your hand and the Colorime-
ter so that no light can enter the Colorimeter.
3. Start data collection in software or on the interface.
4. With your covered hand, rotate the cuvette while observing
the transmittance reading. At the highest transmittance read-
ing, stop rotating.
5. With the cuvette still in the Colorimeter, place one of the
provided arrow labels on the cap with the arrow pointing
toward the screw on the edge of the cuvette holder.
For subsequent measurements and calibrations, always place the
cuvette in the Colorimeter with the arrow pointing toward the
screw. Do not switch caps between cuvettes.
Activity: Transmittance and
Absorbance of Different Colors
Equipment Required: Colorimeter, PASPORT interface, distilled
water, red food coloring, and two cuvettes.
1. Connect the Colorimeter to the interface as described above
(may require PASport Extension Cable).
2. Fill one cuvette with distilled water and screw the cap on
securely.
3. Fill another cuvette with a solution of 2 drops of red food
coloring in 6 ml of water. Screw on the cap, then gently rock
the cuvette to mix the solution without creating bubbles.
4. Put the cuvette containing distilled water into the Colorime-
ter and close the lid.
5. Collect a short run of data.
6. Put the cuvette containing the colored solution into the Colo-
rimeter and close the lid.
7. Collect another short run of data.
Compare the absorbance and transmittance of each color for each
sample. Does the distilled water absorb or transmit one color
more than the others? Which color does the red solution absorb
most? Which color does it transmit most?
Sample data: transmittance of red, orange, green and blue light
through a red solution.
Suggested Experiments
• Beer’s Law: find the relationship between the concentration
and the absorbance of a solution. Use this relationship to
determine the concentration of an unknown sample.
• Reaction rate: measure changing absorbance over time as a
chemical reaction occurs in the cuvette.