Academic Chemistry Computer Lab: Simple Rate Study (26 points)
(page 1 of 3)
Background: With the aid of a palm pilot, students will gather absorbance data for a reaction,
print a graph, and intrepid the results.
Introduction: A kinetic study of a reaction is concerned with measuring the rate at which a
chemical reaction occurs. Such a study involves measuring the concentration of a reactant or a
product during the course of a reaction. A Colorimeter will be used to measure the amount of
light being absorbed by the reacting solution as a function of time. The reaction involved is
represented by the equation: H+ + S2O3-2 =====> SO3-2 + S.
The light absorbed by the reaction should increase as solid particles of sulfur form and grow.
MATERIALS
LabPro interface
computer
Vernier Colorimeter
LoggerPro program
tissues (preferably lint-free)
one cuvette
distilled water
6M HCl (hydrochloric acid: strong irritant)
0.134M Na2S2O3 (sodium thiosulfate: food additive in small quantities)
PROCEDURE
1. Find your goggles.
2. Plug the Colorimeter into Channel 1 of the LabPro interface. Connect the computer to the
LabPro using the interface cable. Boot LoggerPro. Right click the meter readout box. Select
digital meter options. Use the column option and get the meter to display the absorbance
readout. Press the < or > button on the Colorimeter to set the wavelength to 635 nm (Red).
3. Prepare a blank by filling an empty cuvette ¾ full with distilled water. Seal the cuvette with a
lid. 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.
4. Calibrating the Colorimeter.
a. Place the blank in the cuvette slot of the Colorimeter and close the lid. The water and
plastic cuvette will absorb some light. All Absorbance readings will need a correction to
ignore this lost light.
b. Press the CAL (calibration) button on the Colorimeter. When the LED stops flashing, the
calibration is complete. The Absorbance readout should now be zero.
Academic Chemistry Computer Lab: Simple Rate Study (26 points)
(page 2 of 3)
5. Set data collection rate. From the main screen select experiment/data collection. Collect data
for 50 seconds.
6. You are now ready to collect absorbance-time data for the low and higher acid
concentrations.
a. Rinse the clean empty cuvette twice with ~1 mL Na2S2O3. Spent Na2S2O3 can go down
the drain. Fill with 3.0mL Na2S2O3.
b. The following should be done very quickly.
--Add one “vertical” drop of 6M HCl
-- stopper
-- mix (turn upside down so bubble moves to opposite side)
-- clean the outside
-- insert in the Colorimeter
-- close the light shield
-- tap the green button to start data collection.
(You should notice the absorbance increase as the reaction proceeds.)
c. If you are not satisfied with the data, clean the cuvette and repeat step 6 a & b. (You don’t
have to recalibrate the Colorimeter.) If you are satisfied with the data, title and print your
graph.
7. Repeat procedure 6, however this time add two “vertical” drops of acid.
Data from unknown amount of 6M HCl
time
time
(sec)
ABS
(sec)
ABS
0
0.001
11
0.288
1
0.024
12
0.370
2
0.030
13
0.426
3
0.037
14
0.482
4
0.048
15
0.536
5
0.063
16
0.588
6
0.084
17
0.635
7
0.113
18
0.678
8
0.148
19
0.718
9
0.189
20
0.751
10
0.237
21
0.779
time
(sec)
22
23
24
25
26
27
28
29
30
31
32
ABS
0.804
0.826
0.853
0.869
0.882
0.896
0.907
0.917
0.928
0.936
0.944
time
(sec)
33
34
35
36
37
38
39
40
41
42
43
ABS
0.952
0.962
0.970
0.974
0.982
0.988
0.990
0.998
0.999
1.004
1.007
Name _________________________________ period _____
Lab Partner _______________________________________
Academic Chemistry Computer Lab: Simple Rate Study (26 points)
(page 3 of 3)
Questions:
1. Describe how concentration affects the rate of this reaction.
2. Justify your answer in question one in terms of atomic collisions.
3. Describe how temperature might affect reaction rate.
4. Three milliliters 0.134M sodium thiosulfate were reacted w/ an unknown amount of 6M HCl.
The data is shown on page 2. “ABS” stands for the unitless term absorbance. How does the
reaction rate of the above data compare with the rates you have studied?
5. Speculate about the acid concentration used to generate the data found on page 2.
Summary: Your lab report should contain the following:
(10 points) Answers to lab questions
(8 points) A plot of absorbance vs time for various acid concentrations
(8 points) Graph of data from page 2.
Remember:
Graphs without titles and units are useless.
No credit is given for Xerox copies.