Colorimeter LAB:
Method of Initial Rates
SAFE WORK PROCEDURE
LOCATION
WRITTEN BY:
APPROVED BY:
DATE CREATED
H. Teller
Troy Scott
Oct. 2, 2013
Fort Richmond Collegiate
LAST REVISION
new
PERSONAL PROTECTION EQUIPMENT (PPE)
Safety glasses or face shield must be worn
at all times in work areas.
Long and loose hair must be tied back
Rings and jewelry (long necklaces /
bracelets, etc.) must not be worn.
Close fitting/protective clothing must be
worn. Remove strings hanging from
pullovers/sweaters.
Appropriate footwear must be worn. Shoe
must be fully enclosed. No open toed
shoes.
HAZARDS PRESENT
HCl can cause burns to skin.
Broken and chipped glassware
can cause cuts.
APPARATUS / MATERIALS
ADDITIONAL
REQUIREMENTS
Vernier Hand held LabQuest mini- Equipment orientation.
interface, colorimeter, cuvettes and WHMIS
caps, 3-pipettes (2.0 mL), 1 small test
tube, small (~50 mL ) beaker,
hydrochloric acid (6.00 M), sodium
thiosulfate (0.20 M), distilled H2O.
SAFE WORK PROCEDURE
Part 1: Hand Held Set Up
1. Plug the hand-held interface into the wall outlet, and turn on the interface (top left corner).
2. Now plug in the colorimeter into one of the channels on the back of the interface. The
monitor will now show absorbance, and the y-axis of the graph will be measuring
absorbance.
3. Pull out the stylus. Familiarize yourself with the menu on the top; graph, data table, etc.
Part 2: Calibrating the Colorimeter:
1. Press the > button on the colorimeter to select the 635 nm wavelength setting for this
experiment.
2. Place ~4.0 mL of distilled water in a clean cuvette and place the cap securely on top. Place
the cuvette into the colorimeter and close the lid (lid side up). (Check orientation of the
cuvette - clear side lines up with arrow – if older cuvettes are used).
3. Next, press the blue CAL button to begin the calibration process. Release the CAL button
when the red LED begins to flash. This light is located underneath the CAL button, so watch
how you place your finger on the button, so that you can see the light.
4. When the LED stops flashing, the calibration is complete and your unit is ready to collect
data. The absorbance should read 0.000 on the hand-held.
Procedure:
You will test four solutions as shown below. You must determine the concentration of each component for
each trial (after mixing) and enter values in your data table.
The general procedure for each trial is as follows:
1. Wear your goggles for the duration of the lab.
2. When pipetting, be sure to hold the pipette from the glass and not from the rubber bulb
3. Measure the liquids needed for Component B (HCl) directly into the cuvette using a pipette,
measuring as accurately as possible. If diluting the acid, place the water into the cuvette
first, before adding the acid.
4. Use caution when handling the acid. If spills occur, clean the area immediately. If you get any on your
skin or clothes, rinse immediately with tap water.
5. Measure the liquids needed for Component A (Na2S2O3) into a small test-tube using a pipette.
6. Return to your station and prepare quickly, but carefully, add Component A to the same cuvette as
Component B, and put a cap on the cuvette.
7. Quickly invert the cuvette to mix the components, put the cuvette into the colorimeter (lid side up), and
close the colorimeter lid.
8. Click collect (green button on bottom of screen) to begin recording data. The graph should begin to go
up after a minute or two. After climbing for some time the “curve” should level out. Click “stop” (red
button) at this point. The graph will stretch out at this point.
9. On the top of the screen, tap on “analyze”. On the pull-down menu, checkmark “tangent”. Tap your
stylus on the steepest, straight-line portion of your curve to get the slope. Try this in a few different
positions to see that you have the steepest point. Record this value for slope in your data table.
10. Push the record button and it’ll ask you if you’d like to save, append, or discard the data. Tap discard.
11. Repeat the above procedures for solutions #2-4, recording your slope for each in your data table.
12. Dispose any excess acid to the container at the front teacher station.
REGULATORY REQUIREMENTS


WS&H Act W210, Section 4, 5
Mb. Regulations 217/2006,
Part 16, (Machines / Tools & Robots) Sections 16.1-16.18)
Part 35, (WHMIS Application)
Part 36, (Chemical & Biological Substances Application)
Experiment: Rate of a Chemical Reaction
Chemistry 42S
Name:____________
Lab Partners: _____________________________
Prelab Questions: Answer these in your lab journals. You may cut out and paste the tables
in your journal.
1. What different ways can the rate of a chemical reaction be measured?
2. What information does a reaction order tell us?
3.
The reaction A + B → C is first order in A and B, second-order overall. Complete the
following table:
Initial Concentration (mol/L)
[A]
0.50
0.50
0.25
4.
Initial Rate (mol/L s)
[B]
0.50
0.20
0.040
1.0
The reaction CoBr(NH3)52+ + OH- → Co(NH3)5OH2+ + Br- was studied at 25oC, and the
following initial rate data were collected:
CoBr(NH3)52+ M
0.030
0.060
0.030
0.090
OH- M
0.030
0.030
0.090
0.090
Rate (Ms-)
1.37x10-3
2.74x10-3
4.11x10-3
1.23x 10-2
Determine the rate law, the overall order and the value of the rate constant for the reaction.
Purpose:
In this laboratory activity you will investigate the effect of changes in concentration of the
reactants on the rate of a reaction. The colorimeter will measure the change in absorbance of
light of a solution during the chemical reaction. The rate of change of absorbance is measured
for different concentrations of the chemicals in the reaction. The hand-held Vernier program
records and displays data.
Theory:
In this experiment you will determine the effect of changes in concentration of the reactants on
the rate of the chemical reaction. The reaction chosen for this experiment is the acidic
reduction of the thiosulfate ion (S2O32-) to sulphur and sulphur dioxide:
S2O32-(aq)
+ 2 H+(aq) → SO2(g) + S(s) + H2O(l)
(from NaS2O3) (from HCl)
In order to determine the effect of concentration on the rate of the reaction, you will follow the
reaction by using the colorimeter to monitor the formation of the solid sulphur generated. The
solid sulphur will block the light in the colorimeter and the amount of blockage is directly
proportional to the amount of sulphur in suspension.
The rate of this chemical reaction is given by the equation: Rate = k [S2O32-]x[H+]y
Equipment Needed: See SWP above
Procedure: See SWP above
Data: Complete the chart, including your values obtained from the graph.
Show your calculations for concentration in the chart below.
Calculation of Concentration
Solution
sodium thiosulfate is 0.20 M
HCl is 6.0 M
concentration = moles
total volume
[A]
A: 2.0 mL thiosulfate
#1
B: 2.0 mL HCl
A: 2.0mL thiosulfate,
#2
B: 1.0 mL HCl +
1.0 mL H2O
#3
A: 1.0 mL thiosulfate +
1.0 mL water
B: 2.0mL HCl
#4
A: 0.5mL thiosulfate +
1.5 mL water,
B: 2.0mL HCl
=
CXV
total volume
[B]
Tangent Line
Slope/Rate
Calculations:
Show all you work in determining the order of reaction due to both thiosulfate and the acid and
the overall rate law. Be sure to look at all possible ways to determine rate order for a given
substance, since your data may not be easy to interpret.
Calculate the rate constant, k, for this reaction.
Questions:
1. Does your data make sense? Explain why or why not?
2. What would be the rate of reaction if we began with 2.0 mL of 0.10 M thiosulfate and 2.0
mL of 4.0 M HCl?
3. What would happen to the rate of the reaction if you tripled the rate of the thiosulfate,
and quadrupled the acid?
Conclusion:
Summarize the lab, indicating the rate law found, using data to support your claims.
Sources of Error:
Give two sources of error in this lab and state the effect each would have on the final results.