the reaction to start and progress. After this the absorbance values of the solution were recorded every 30
seconds. Finally, data was observed graphically using MS Excel. The absorption values vs. time were
graphed in 3 ways (absorption value vs. time, ln(absorption value) vs. time, and 1/(absorption value) vs.
time) to determine the order with respect to crystal violet.
RAW DATA
Time (min)
Absorbance (A
565
)
0:00
0.135
3:00
0.049
3:30
0.035
4:00
0.022
4:30
0.013
5:00
0.009
5:30
0.001
(See Appendix for the three graphs of absorption vs. time)
CALCULATIONS/RESULTS
Rate constant (k) =
-slope of linear regression line =
0.0263 mol/L*s
Half-life = Graphically:
1
st
half-life = 2:45 min, 2
nd
half-life = 45 s
Calculation:
1
st
half-life
= [A]
o
/2k = .135 M/2(0.0263 mol/L*s) = 2.57 =
2:34 min
2
nd
half-life
= [A]
o
/2k = .0675 M/2(0.0263 mol/L*s) = .54 =
32 s
SUMMARY/DISCUSSION
The reaction order in respect to the concentration of crystal violet was zero, as evident by the
linear relationship in the zero order graph. Rate law is written k[A]
order
[B]
order
, so the rate law for this
reaction, in terms of crystal violet since sodium hydroxide concentration did not change appreciably, is
rate = 0.0263 mol/L*s
. The 1
st
half-life obtained graphically varied by 7% from the 1
st
half-life obtained
by calculation, while the 2
nd
half-life obtained graphically varied by 38% from the 2
nd
half-life obtained
by calculation. This variation is due to the graph size and the large increments between absorbance
values which made it difficult to estimate what the time is at the right absorbance value. One
improvement on this experiment would be to record absorbance values earlier than 3 minutes and more
often than 30 seconds, since the reaction happened so quickly and only a few absorbance values were
able to be recorded before the absorbance reached zero.

Appendix
Time
(min)
Absorbance (
Absorbance
0
0.135
3
0.049
3.5
0.035
4
0.022
4.5
0.013
5
0.009
Time
(min)
ln(Absorban
Absorbance
0
-2.002480501
3
-3.015934981
3.5
-3.352407217
4
-3.816712826
4.5
-4.342805922

5
-4.710530702
Time
(min)
1/(Absorban
Absorbance
0
7.407407407
3
20.40816327
3.5
28.57142857
4
45.45454545
4.5
76.92307692
5
111.1111111

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- Spring '15
- Dadabay
- Chemistry, Reaction, Rate equation, crystal violet-sodium hydroxide