CHEMICAL KINETICS: RATES OF CHEMICAL REACTIONS
Consider
the following set of reactions where the letters (AL) represent different
chemicals.
In
order for the end product “L” to be formed, only “A”, “B”,
“E”, and “K” must initially be present.
All other chemicals needed for the formation of “L”
are produced from reactions between these ‘original’ chemicals and from
reactions between the byproducts of those reactions. (To convince yourself of this work backwards from the last
reaction).
However,
when “I” is produced in reaction (3), it has two possible fates.
It can react with “C” and “H” or it can react with “K”.
Therefore, reactions (4) and (5) are competing.
If
reaction (5) occurs more slowly than reaction (4), then “L” will only
be produced in any significant quantity when the supply of either “C” or
“H” are exhausted. Ultimately,
the availability of “C” is dependent on the supply of “A” and
“B”.
Experiment
Overview
The reactions for today’s experiment are the following: (Note the letters in bold represent the letters in the generic example previously described. The reactions are purposely unbalanced for simplicity.)
(A)
NaHSO_{3}
+ (B) H_{2}SO_{4}
à (C) H_{2}SO_{3} + (D) NaHSO_{4}
(1)
(E)
KIO_{3}
+ (C) H_{2}SO_{3}
à (F) KI +
(B) H_{2}SO_{4}
(2)
(E)
KIO_{3}
+ (B) H_{2}SO_{4}
+ (F) KI à (G) K_{2}SO_{4}
+ (H) H_{2}O
+ (I)
I_{2}
(3)
(I)
I_{2}
+ (C) H_{2}SO_{3}
+ (H) H_{2}O
à (B) H_{2}SO_{4} + (J) HI
(4)
(I)
I_{2}
+ (K) starch
à (L) starch• I_{2} complex
(blueblack in color)
(5)
Equations
(1) through (4) continue until all of the NaHSO_{3}
is gone. Then the I_{2}
is no longer consumed by reaction (4) so I_{2} reacts with starch
to form a complex that is blueblack in color.
Solution
1 is a solution of potassium iodate (KIO_{3})
Solution
2 is a solution containing sulfuric acid (H_{2}SO_{4}),
sodium bisulphate (NaHSO_{3}), and starch.
(refer
to the above set of chemical equations to see how and when these compounds
react)
Activity, Part
1
1. Use a pipette to
dispense 5.0 mL of Solution 2 into a clean (if you are
using a recycled test
tube, rinse it with RO Water first) test tube.
2. Add the appropriate
amount of RO Water to the tube using a different pipette.
3. Add the appropriate
amount of Solution 1 to the tube using another pipette.
4.
Cap the tube and invert four times.
5.
Begin timing after the fourth inversion.
6.
End timing as soon as the solution changes from colorless to blue/black.
(You only need to time to the
nearest second.) Your
instructor will have a color standard against which you
can compare.
Experimental Procedure.
The effect of concentration of
the potassium iodate can be determined by using different ratios of Solution
1 to RO Water.

#1 
#2 
#3 
#4 
#5 
#6 
#7 
#8 
#9 
#10 
Unknown 
Amount of Solution 2 (mL) 
5.0 
5.0 
5.0 
5.0 
5.0 
5.0 
5.0 
5.0 
5.0 
5.0 
5.0 
Amount of
RO Water (mL) 
0 
0.5 
1.0 
1.5 
2.0 
2.5 
3.0 
3.5 
4.0 
4.5 
0 
Amount of Solution 1 (mL) 
5.0 
4.5 
4.0 
3.5 
3.0 
2.5 
2.0 
1.5 
1.0 
0.5 
5.0 (unknown) 
Be sure
to replicate each treatment THREE times. Record
your data on PAGE 4.
Analysis:
Effect of Concentration
Solution 1 Concentration 
Trial #1 
Trial #2 
Trial #3 
Average T 
1/Avg. T 




























































UNKNOWN 





3.
What would happen if you doubled the amount of Solution 2 without
changing either the
amount of Solution 1 or RO water used?
Why?
4.
Graph the relationship between the concentration of Solution 1 and the
reaction time. To
make the graph easier to construct (and interpret), plot the
reciprocal of the reaction time
(1/Average T) rather than the actual average.
5.
Based on the graph and your data for the unknown solution, what is the
concentration of this
solution?
Activity,
Part 2 The Effect of
Temperature on Reaction Rate
Analysis:
Effect of Temperature
Temperature 
Trial #1 
Trial #2 
Trial #3 
Average T Time Tim Time 
1/Avg T 






























UNKNOWN 





1. Make a generalization concerning the effect of temperature on the rate of reaction. Give a causal explanation for this generalization.
2.
Graph the relationship between temperature and reaction time as you did
earlier, plotting the reciprocal of reaction time (1/Average T) rather than the
actual average.
3.
Based on the graph you constructed and your data for the temperature
unknown, what is the temperature of this solution?