CHM 101/102
Kinetics
General Chemistry 101/102
Laboratory Manual
University of North Carolina at Wilmington
Laboratory Manual
CHM 101/102
Kinetics
•
Purpose
 To determine the rate law and the value of the
reaction rate constant for a chemical reaction
using the method of initial rates.
•
Safety Considerations
 Wash your hands thoroughly after handling
chemical reagents and before leaving the lab.
 All chemical wastes should be placed in the
labeled jar in the hood.
Laboratory Manual
CHM 101/102
Kinetics
•
Background
 The chemical reaction being studied in this
experiment is:
6 I- + BrO3- + 6 H+
3 I2 + Br - + 3 H2O
bromate ion
 The general rate law for this reaction can be
written as:
- D [BrO3-]
Rate =
= k [I-]x [BrO3-]y [H+]z
Dt
 By measuring the rate of the reaction as we vary
the concentrations of I-, BrO3-, and H+, we can
determine the values of x, y, and z.
Laboratory Manual
CHM 101/102
Kinetics
•
Background
 Since BrO3- is colorless, we need some way to
determine when a certain amount of BrO3- has
reacted.
 To do this, we will add S2O32- and starch to the
reaction mixture. S2O32- reacts very rapidly with I2
as shown below:
I2 + 2 S2O32thiosulfate ion
2 I- + S4O62tetrathionate ion
 When all of the S2O32- is used up, any I2
that remains will react with the starch to
produce a deep-blue colored complex.
Laboratory Manual
CHM 101/102
Kinetics
•
Background
 The concentration of S2O32- in each trial is 2.0x10-4 M.
Since there are 6 moles of S2O32- reacted for every
1 mole of BrO3- reacted, then the concentration of
BrO3- reacted in each trial is 3.3x10-5 M.
 By measuring the time it takes for the blue color to
appear in each trial, we can determine the rate of
the reaction for each trial.
- D [BrO3-]
3.3 x 10-5 M
Rate =
=
Dt
Dt
Laboratory Manual
CHM 101/102
Kinetics
•
Procedure
 Each trial is performed in the same manner. Use a
10 mL graduated cylinder to measure the quantities
shown in Table 1 for Trial 1 into flasks labeled “A” and
“B”.
Laboratory Manual
CHM 101/102
Kinetics
•
Procedure
 Add 4 drops of starch solution to the
flask labeled “B”.
B
 Quickly pour the contents of flask “B” into flask “A”
and start the stopwatch. Record the time it takes for
the solution to turn blue. Record the temperature of
the blue solution.
A
Laboratory Manual
B