Nia kaings
Experiment 7: lodine Clock Reaction Kinetics
CHEMISTRY REVIEW TOPICS
Reading: OpenStax, Chemisi, 2e, Chapter 12, Scctions 12.1 to 12.3
YouTube Video: Kinctics: Chemistry's Demolition De
y. (First 6 min. of video are most relevant,)
YouTube Video: The Arhenius Equation, Activation Encrgy, and Catalysis Explained Pt 8
SAFETY
Hot Equipment: Be careful with the hot plates. They remain hot for a long time
after switched off.
Chemical waste: All chemicals can be disposed of in the sink followed by rinsing.
INTRODUCTION:
In this experiment, you will determine a reaction rate and
the effect of changing reactant
concentration and temperature on reaction rate of a chemical
eaction. The reaction chosen proceeds
conveniently slowly near room temperature and can easily
e measured by observing a dramatic
color change. The reaction is the oxidation of iodide ion (I)
to molecular iodine (l») by hydrogen
peroxide (H202):
:02+2H+21 » +2 HO slow (Eqn. 1)
As the reaction proceeds, the colorless reactants gradually generate
own l2 product. It is difficult
to time the appearance of Iz, therefore, we make
use of a second much faster reaction in the
same
solution to measure the progress of the slow
eaction: Starcih
Eqn. 2) GddedasS
Ia+2 S20s-21+S40 fast an.indCaHOr
Reaction 2 is so fast that I2 produced by reaction
1 is consumed instantaneously by thiosulfate
(S20), preventing the
own l2
color appearance. Because both S:0 and S4Oare colorless,
therefore the solution remains
colorless. However, less thiosulfate is added than
will consume all
the I2 that will be formed from
eaction 1. Therefore the reaction solution stays
colorless until the
instant at which all the thiosulfate is
consumed. The reaction is timed starting at initial mixing
until
the appearance of color from I2.
To help visualize the appearance of I2
starch indicator is added to
give an intensely colored
dark complex.
The stoichiometry of the two
eactions will allow the determination of
the reaction rate in terms of
H:02 by mcasuring the change in
S,0as follows:
A,0]A L A,L 1AS,O;]
2 Ar rate of reaction = Ar A Ar
By repeating the experiment
with different concentrations of H202 and
different temperatures, we
can determine the effect of changing H20
concentration and temperature on the rate of
eaction 1.
During a chemical reaction, bonds are
oken in reactants and new bonds are formed in the
products. Reactions can only occur
if reactant molecules collide with each other. These
collisions
Reagent Concentrations: 0.10,M HI, 0.20M H;02, 0.15 M S:0
Run 1 Run 2 Run 3 Run 4 Run 5
1., seconds Q0L.lo sad Y1.o80.Ysesec
Ia.&G11.1°C1,5C| 319C|0G
3.H:0:1 M 0.0OM O.0M. O.a0M o.20M 0.a0M_
5-1,M0.15MO.15M|o.5M o.1SM_ o.5M
2. Temp. 'C
5. AS:0I. M
6. A H:0:], M
7. Rate, M/s
8. k, s
9. In k
10. 1/T, K
In the spaces below, show the following
calculations for Run 1.
3. [H0] M
O.9ON
MIV
V
4. [S014 M
O.15 M
5. AS2021, M
7. Rate, Mis
8. k,s s1
9. In k
10.1/7, K
1. Using the MS Excel graph
ased on your experimental
data provide the following
information:
Show work where requested
for credit.
a) The slope for In k vs. 1/T graph
straight line is
) The units for slope are
Show calculations in the space
elow.
c)The activation energy (E.)
is
.
Show calculations in the space
helow.
d) The frequency factor (A) is_
Show calculations in the space below
2. Use the data from Runs 1, 2 and 3 confirm that Rcaction I is first-order
in H20D.
Additional Questions
1. What is the effect of increasing [H:Q2]/ on the rate of reaction in the experiment?
Whan Ha0 iNCicad ha Yole of Leacion inckoKO.
2. What is the effect of increasing the temperature on the rat� of reaction
in the experiment
ncea sing the teperoBwe sfeed up
tN rale ot
Caction.
3. Iodide ion is oxidized in acidic solution to
triiodide ion (l;") by hydrogen peroxide.
H2Oz(aq)+ 31(ag) +2H (ag) > Is (ag) +2H20()
The following data were obtained from 4 experiments
that varied the initial reactant
concentrations. Use to answer questions a and b.
Initial Concentrations (M)
H202 H
Initial Rate [M/s]
Exp XXXXXXXXXX00050
1.15 x 106
Exp. 2|
Exp.3L
Exp. 4
0.00050
0.00050|
XXXXXXXXXX
2.30 x 10°
2.30 x 106
1.15 x 10
XXXXXXXXXX
XXXXXXXXXX
a) Detemine the rate law for
the above reaction.
) Detcrmine the rate constant of the reaction.