Running Head: CHEMICAL KINETICS LAB 1
Chemical Kinetics Lab
Prepared for: Mrs. Freeman
February 6, 2014
Introduction
CHEMICAL KINETICS LAB 2
The science of chemistry is, in the simplest context, the formation of substances from
other substances; in other words, the concept of the chemical reaction is at the very core of all
chemistry. In turn, chemical kinetics, the study of the rates these chemical reactions, is also of
paramount importance (Kinetics, n.d.).
Chemical kinetics involves the concepts of reaction rates and rate laws. Reaction rates
can be the rate at which a product/reactant is formed/used in a reaction and rate laws are the
definitions that govern the aforementioned rates of appearance/disappearance. Many factors
affect the rate of a reaction. First, the concentration of the reactants plays an important role, as
increased concentrations usually correlate to a faster reaction. Increased temperature similarly
affects rate, as well as increased surface area of the reactants. Finally, the presence of a catalyst
decreases the activation energy of reaction, in turn speeding up the reaction (Intro to Kinetics,
n.d.)
Furthermore, these concepts are not confined to theoretical use. One example of a real
world application of rate law is found in the use of pesticides. When pesticides are used in an
environment to keep insects away, rainfall and other sources of water, such as sprinklers, will
wash off the pesticides from the plants, and the runoff will contain traces of these pesticides. To
prevent the contamination of freshwater sources, such as rivers, scientists must find and create
pesticides that dissolve into non harmful chemicals when reacted with water, and this rate of
reaction is of utmost importance (Mathematical Prediction, n.d.)
Another use of rate law can be found in enzymes. Enzymes are biological catalysts that
cause biochemical reactions. The rate of these biochemical reactions is very important in many
processes, such as food digestion. Digestive enzymes located in the stomach help break down
CHEMICAL KINETICS LAB 3
food that is ingested, and the determination of the average rate of this digestion can be used to
develop digestive supplements for those with digestion problems (Chymotrypsin, n.d.).
Finally, the concept of reaction rates are used in nuclear decay and areas that deal with
nuclear decay. For example, the dating of ancient organisms using Carbon-14 is a manipulation
of rate law. All living creatures contain carbon, and this technique of dating is widely accepted
Carbon-14 slowly decays, and using the concepts of decay kinetics and the rate of decay of
Carbon-14, scientists can accurately determine the age of fossils and other decomposed organic
material (Decay Kinetics, n.d.)
Purpose:
In this lab, the pseudo rate law governing the reaction between Crystal Violet (CV) and
Sodium Hydroxide (NaOH) will be derived from the gathered data.
Methods:
1. All the materials needed for the lab were obtained.
2. The colorimeter was calibrated. To calibrate the colorimeter, use a pipette and fill one
cuvette 75% full with distilled water and place the cuvette in the colorimeter. The
absorbance should be 0.00. (Note: The colorimeter was set at 565nm because of the CV’s
purple color).
3. In 11 different test tubes, dilutions of the 24.5 μM solution of CV were created with
distilled water, as shown in Table 1.
4. With 11 DIFFERENT PIPETTES for each test tube, 11 different cuvettes were filled
about 75% full of each of the 11 dilutions of CV solution. The absorbance of each was
collected and recorded.
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5. Then, the concentration of each of the dilutions was found using the formula 𝑀1𝑉1 =
𝑀2𝑉2. (Note: The first dilution was essentially only 24.5 μM solution of CV; this
information was used to calculate the concentrations of the other dilutions as shown in
Table 1.)
6. A chart showing the concentration of CV dilutions vs. Absorbance of CV dilutions was
created, as well as a graph of this collected data (Table 1 and Figure 1). The graph was
created with a trend line.
7. The equation of the trend line and the coefficient of determination (R2) of this line was
then found, as shown in Figure 1. The R2 value should be high (>.90). This high value
ensures that the trend line accurately represents the data plotted. Both the equation and R2
value was recorded on the graph created in the previous step (Figure 1)
8. A separate cuvette was filled about 50% full of the 24.5 μM solution of CV using a
different pipette.
9. Next, with a new pipette, a small amount of NaOH solution was obtained. This solution
was then put in the cuvette filled in the previous step, which started to react with the CV.
The cuvette was placed into the colorimeter.
10. The absorbance of the solution of CV and NaOH was then recorded immediately and
every 25 second interval thereafter until the absorbance shown on the colorimeter is 0.00
(or close to it), (Table 2).
11. The equation found in step 7 is defined as absorbance = m(concentration of CV) (where
m is a definite number). Using this equation, the concentration of the solution of CV at
each of the 25 second intervals was determined. This was done by substituting the
CHEMICAL KINETICS LAB 5
absorbance at a specific time into the equation and solving algebraically for the
concentration (Table 3).
12. Next, the natural log of the concentration of CV was determined for each concentration
found in the previous step, as well as the reciprocal of the concentration of CV. (Table 3).
13. A graph was then created containing 3 different graphs: time vs. concentration of CV,
time vs. ln(Concentration of CV), and time vs. 1/(Concentration of CV) (Figure 2). These
3 were also graphed individually with linear trend lines for clarity (Figures 3, 4, and 5).
14. The R2 value of each of the individual graphs (Figures 3, 4, and 5) was found in order to
determine the order of CV in the reaction.
15. With the order of CV determined, the pseudo rate law was found.
CHEMICAL KINETICS LAB 6
Data
Table 1: Concentration of CV Dilutions vs. Absorbance
Dilutions (mL of CV/mL of water) Concentration (μM) Absorbance
10ml/0ml 24.5 1.161
9ml/1ml 22.05 1.12
8ml/2ml 19.6 1.104
7ml/3ml 17.15 1.051
6ml/4ml 14.7 0.967
5ml/5ml 12.25 0.805
4ml/6ml 9.8 0.716
3ml/7ml 7.35 0.546
2ml/8ml 4.9 0.36
1ml/9ml 2.45 0.169
0ml/10ml 0 0
Table 2: Time vs. Absorbance during reaction between CV and NaOH
Time (s) Absorbance
0 1.01
25 0.915
50 0.818
75 0.718
100 0.622
125 0.533
150 0.454
175 0.384
200 0.324
225 0.224
250 0.231
275 0.193
300 0.162
325 0.136
350 0.113
375 0.094
400 0.078
425 0.064
450 0.053
475 0.044
500 0.036
525 0.03
550 0.025
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Table 3: Time vs. Concentration, ln (Concentration), and 1/Concentration of CV
Time Concentration Ln[Concentration] 1/Concentration
0 17.93960924 2.887011075 0.055742574
25 16.25222025 2.78822953 0.061530055
50 14.52930728 2.676167801 0.068826406
75 12.75310835 2.545775034 0.078412256
100 11.04795737 2.402245558 0.090514469
125 9.46714032 2.247826889 0.105628518
150 8.063943162 2.087402663 0.124008811
175 6.820603908 1.919948017 0.146614583
200 5.754884547 1.750048981 0.173765432
225 3.978685613 1.380951517 0.251339286
250 4.103019538 1.411723175 0.243722944
275 3.428063943 1.231995654 0.291709845
300 2.877442274 1.0569018 0.347530864
325 2.415630551 0.881960351 0.413970588
350 2.007104796 0.696693284 0.498230088
375 1.669626998 0.512600247 0.59893617
400 1.385435169 0.326014292 0.721794872
425 1.136767318 0.128188548 0.8796875
450 0.941385435 -0.060402622 1.062264151
475 0.781527531 -0.246504901 1.279545455
500 0.639431616 -0.447175597 1.563888889
525 0.53285968 -0.629497153 1.876666667
550 0.444049734 -0.81181871 2.252
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Figure 1: Concentration vs Absorbance of Dilutions of CV
Figure 2: Time vs. Concentration, ln (Concentration), and 1/Concentration of CV
y = 0.0563xR² = 0.9067
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 5 10 15 20 25 30
AB
SOR
BA
NC
E
CONCENTRATION (MICROMOLAR)
CONCENTRATION VS. ABSORBANCE OF DILUTIONS OF CV
-5
0
5
10
15
20
0 100 200 300 400 500 600
CO
NC
ENTR
ATI
ON
(M
ICR
OM
OLA
R)
TIME (S)
T I M E V S . C O N C EN T R A T I O N , L N ( C O N C EN T R A T I O N ) , 1 / C O N C EN T R A T I O N
Concentration ln(Concentration 1/Concentration
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Figure 3: Time vs. Concentration of CV (0th Order)
Figure 4: Time vs ln (Concentration of CV) (1st Order)
R² = 0.8615
-5
0
5
10
15
20
0 100 200 300 400 500 600
CO
NC
ENTR
ATI
ON
[M
ICR
OM
OLA
R]
TIME (S)
TIME(S) VS. CONCENTRATION OF CV
R² = 0.9962
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
3
3.5
0 100 200 300 400 500 600
LN[C
ON
CEN
TRA
TIO
N]
(MIC
RO
MIL
AR
)
TIME (S)
TIME (S) VS. LN[CONCENTRATION OF CV]
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Figure 5: Time vs 1/Concentration of CV (2nd Order)
R² = 0.7783
-0.5
0
0.5
1
1.5
2
2.5
0 100 200 300 400 500 600
1/C
ON
CEN
TRA
TIO
N (
MIC
RO
MIL
AR
)
TIME (S)
TIME (S) VS 1/[CONCENTRATION OF CV]
CHEMICAL KINETICS LAB 11
Calculations
Concentrations of Dilutions: (Known information: Concentration of 10 mL/ 0 mL = 24.5
μM)
Using 𝑀1𝑉1 = 𝑀2𝑉2:
Ex) 9mL/1mL: (24.5 𝜇𝑀)(9 𝑚𝐿) = (? 𝑀)(10 𝑚𝐿); (24.5 𝜇𝑀)(9 𝑚𝐿)
10 𝑚𝐿= ?𝑀 =
22.05 𝜇𝑀
Process repeated for each dilution
Equation/ Coefficient of Determination (R2) of Trend Line of Figure 1 (Found on Excel)
y = 0.0563x
R² = 0.9067
Concentration of CV when reacted with NaOH (Table 3)
Using above trend line
Ex) 𝑦 = 𝑎𝑏𝑠𝑜𝑟𝑏𝑎𝑛𝑐𝑒 𝑜𝑓 𝐶𝑉 = 1.01
𝑥 = 𝜇𝑀 𝑜𝑓 𝐶𝑉 = ?
0.0563𝑥 = 1.01
𝑥 =1.01
. 0563
𝑥 = ?= 17.94 𝜇𝑀 𝑜𝑓 𝐶𝑉
Repeated for all absorbances in Table 2
R2 value of Figures 3, 4, and 5
Figure 3 (0th order) - .8615
Figure 4 (1st order) - .9962
Figure 5 (2nd order) - .7783
CHEMICAL KINETICS LAB 12
Analysis
The purpose of this lab was to find the pseudo rate law of the reaction of Crystal Violet
(CV) and Sodium Hydroxide (NaOH). The reaction of CV and NaOH can be written in net ionic
form as shown below:
𝐶𝑉+ + 𝑂𝐻− 𝑦𝑖𝑒𝑙𝑑𝑠→ 𝐶𝑉𝑂𝐻
This, in turn, means that the rate law of CV and OH is defined as
𝑅𝑎𝑡𝑒 𝐿𝑎𝑤 = 𝑘 [𝐶𝑉]𝑥[𝑂𝐻]𝑦
Where x is the order of CV in the reaction, y is the order of OH in the reaction, and k is the rate
constant that governs the reaction. However, the concentration of OH- ions in the reaction was so
high compared to the CV ions that the value of [OH] y almost remains constant, allowing the rate
shown above to be substituted with a pseudo rate law defined as
𝑅𝑎𝑡𝑒 𝐿𝑎𝑤 = 𝑘∗[𝐶𝑉]𝑥
𝑘∗ = [𝑂𝐻]𝑦
Now, with the pseudo rate law properly defined as an equation, the missing component
that made the pseudo rate law complete was the value of x, the order of CV. To find the order of
a reactant in any reaction, two aspects of the reaction are needed: the time within which the
reaction takes place, and the changing concentration of the reactants at during this time. To find
these aspects, the properties of Beer’s law that connects absorbance and concentration were
utilized. First, as shown in Table 1, dilutions of CV and distilled water were made, and the
absorbance of each was found using a colorimeter. Then, using the known molarity of the 10
mL/ 0mL dilution (24.5 μM) and 𝑀1𝑉1 = 𝑀2𝑉2 , the concentrations of all the dilutions were
calculated (Table 1). This information was then rearranged and graphed as Concentration vs.
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Absorbance of CV dilutions in Figure 1, and the equation of the trend line was found. This
information was crucial later in the lab.
Next, a small amount of CV and NaOH were reacted in a cuvette, and the absorbance of
this solution was measured consistently every 25 seconds. The absorbance fell dramatically, due
to the fact that when the hydroxide ions reacted with the vibrantly purple CV, the solution slowly
became transparent. This data is shown in Table 2. Now, with the equation of the trend line
found in Figure 1, the concentration that correlated with each absorbance in Table 2 was found,
as shown in the calculations section of this report. This means that, after some manipulation of
charts and data, time and concentration of CV, the two components needed to find the order of
the CV, have been found (Table 3).
The final step to finding the order of CV is to determine which manipulation of the
concentration graphed against the time yields the straightest line. These graphs are defined as
time vs concentration of CV (Figure 3), which represents the 0th order, time vs. ln (concentration
of CV) (Figure 4), which represents the 1st order, and time vs. 1/ (concentration of CV) (Figure
5), which represents the 2nd order. To determine which yielded the straightest line, the R2 value
of a linear trend line was found for each graph. Statistically speaking, the higher the R2 value, the
more of the data can be explained by the trend line. The first order graph had the highest R2
value (.9962), which means that 99.62% of the data could be explained by the linear trend line.
In other words, 99.62% of the data was completely in line with the trend line, making it the
straightest data regression of the 3 orders. Therefore, the order of CV was found to be 1.
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Error Analysis
The results of the experiment and the subsequent analysis of the data seem to be very
sound. While there was a rush for time and the reaction could not completely go to completion
(absorbance of CV and NaOH solution is 0), this does not seem to have had a large effect on the
data at all.
Conclusion
The pseudo rate law that governs the reaction between Crystal Violet and Sodium Hydroxide
was found to be:
𝑅𝑎𝑡𝑒 𝐿𝑎𝑤 = 𝑘∗[𝐶𝑉]1
𝑘∗ = [𝑂𝐻]𝑦
CHEMICAL KINETICS LAB 15
References
Chymotrypsin. (n.d.). - Chemwiki. Retrieved February 5, 2014, from
http://chemwiki.ucdavis.edu/Physical_Chemistry/Kinetics/Case_Studies/Chymotrypsin_
II
Decay Kinetics - variation of decay rate with time. (n.d.). Decay Kinetics - variation of decay
rate with time. Retrieved February 5, 2014, from
http://www.science.uwaterloo.ca/~cchieh/cact/nuctek/decaykinetics.html
Introduction to Chemical Kinetics, First Order Precesses, Half-Life. (n.d.). Introduction to
Chemical Kinetics, First Order Precesses, Half-Life. Retrieved February 5, 2014, from
http://www.chem.arizona.edu/~salzmanr/480a/480ants/kinintro/kinintro.html
Kinetics - The Rate Law. (n.d.). Kinetics - The Rate Law. Retrieved February 5, 2014, from
http://bouman.chem.georgetown.edu/S02/lect2/lect2.htm
Mathematical Prediction of Cumulative Levels of Pesticides in Soil. (n.d.). - Organic Pesticides
in the Environment. Retrieved February 5, 2014, from
http://pubs.acs.org/doi/abs/10.1021/ba-1966-0060.ch010