Research topic

Investigating orders of reaction and
activation energy for the reaction between potassium permanganate and
ethanedioic acid using a colorimeter.

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Research question

What is the activation energy for the reaction
of potassium permanganate with ethanedioic acid?

Personal engagement and aim

There are widespread skin conditions from
which many people suffer, particularly teenagers due to the transition period
they experience.1
One of these conditions is Eczema Dermatitis.2 There are many types of
Eczema, one of which is Exudative Eczema.3 As a teenager, I developed
an interest in researching the treatments of these skin conditions. I found out
that Exudative Eczema can be treated with potassium permanganate.4 Moreover, I became more
interested in the kinetics of potassium permanganate, as kinetics is an
important concept to consider in reactions which takes place to produce
medications. In addition, I found out that potassium permanganate is on the WHO
model list for essential medications,5 which makes it more
important to investigate its applications and kinetics.

This
investigation’s aim is to find the reaction orders for the reaction of potassium
permanganate with ethanedioic acid. Afterwards, the information gained will be used
to determine the rate constants for the reaction at different temperatures, so that
the activation energy can be worked out.

Background information

The activation energy is defined as the
minimum amount of energy required for a reaction to occur.6 For a successful reaction
to occur, the collision theory7 states that particles must
collide in the correct orientation, and with energy that equals or is greater
than the activation energy. Figure 1SK1 8 illustrates how a transition state is reached when reactants have
sufficient energy, and hence products are formed.

To carry out a
successful reaction, we should be aware of its activation energy. This value
can be found through multiple experimental steps: ?rstly, determining the
orders of reaction, which can be defined as the relationship between the
overall rate of reaction and the concentration of the reactants9. This should be done for
each reactant through changing the concentration of one reactant, without
altering the concentration of the others, to see its effect on the overall rate
of reaction at each concentration. There are two methods to determine the value
of the reaction order: graphically or mathematically. The trend line on the
rate-concentration graph, as shown
in ?gure 2,10
indicates a specific order of reaction. Mathematically, information from table
(1)11, 12 can be used to work out
the order of reaction.

Table 1:
information to calculate the order of reaction for each reactant.

Effect on rate when
doubling the concentration of a reactant

Reaction order for
the reactant

The rate is the same

Zero order

The rate doubles

First order

The rate quadruples

Second order

 

To find the rate equation of a reaction, all
reaction orders have to be determined. The rate expression includes the rate
constant (k), which remains constant if the concentration varies, but increases
when the temperature increases.13 Hence, different values
of the rate constant (k) can be determined through carrying out the reaction
with fixed concentrations of the reactants at different temperatures. Increasing
the temperature causes the particles to collide with energy that equals or is
greater than the activation energy.14 Therefore, successful
collision will occur, and it can be concluded that higher temperatures cause
faster rates of reaction. The values for temperature (T), activation energy (Ea),
and the rate constant (k), are incorporated into the Arrhenius equation15 presented below. The
equation can be written in the form y = mx + c, to calculate the activation
energy graphically, as shown below.

   ?   

A is the Arrhenius
constant SK2 which shows the frequency of the collision and their orientation, T
is measured in Kelvin, and R represents the gas constant (8.31 J.K-1.mol-1).16, 17 Thus, by plotting a
graph from the values of (1/T) on the x-axis and ln(k) on the y-axis, the
gradient (m) will be equal to (-Ea/R). The value of m is
therefore used to calculate the activation energy Ea.

Ehtanedioic acid SK3 (C2H2O4), also called oxalic acid,
is a dicarboxylic acid present in many plants and vegetables, and produced by
metabolism in the body.18 It is used as a reducing
agent.19 On the other hand, potassium
permanganate (KMnO4) SK4 is a purple crystalline solid, which is dissolved in water to make
potassium permanganate solution, which is used as an oxidizing agent.20 Potassium permanganate reacts
with ethanedioic acid in the reaction presented belowSK5 .21

2MnO4- + 5H2C2O4
+ 6H+? 10CO2 + 8H2O + 2Mn+2

Initially,
the reaction mixture has a purple color, the color of potassium permanganate.22 On the other hand,
ethanedioic acid is colorless.23 As the reaction proceeds,
potassium permanganate gets used up, and the color of the solution changes from
purple to colorless.24 A colorimeter can be used
to observe the rate of decolorization of potassium permanganate, as it measures
the amount of absorbed light of a certain wavelength through a sample over time.25 Hence, the reaction rate
is the rate of decrease in absorbance. The absorbance of a sample, given by the Beer-Lambert lawSK6 SK7 , is:   where: A is the absorbance, Io
is the intensity of the light passing through the reference cell for each
wavelength of light, and I is the intensity of the light passing through
a sample cell for that wavelength.26 Thus, in this investigation,
Io represents the intensity of the light passing through
distilled water, which the colorimeter was calibrated with, and I
represents the intensity of the light passing through the reaction mixture for
the chosen wavelength. The wavelength chosen in this investigation
is 565nm, because this is the closest wavelength, provided by the settings of
the colorimeter, for the range of yellow, the complimentary wavelength of purple
(figure 3)27,
the color of potassium permanganate.

Method justification

The methodology is a modified version of
“investigating the reaction between manganate(VII) and ethanedioate ions” from the
Royal Society of Chemistry.28

Quantities and concentrations of
chemicals: for the color change to be
distinguishable, potassium permanganate should always is kept as the limiting reactant,
otherwise the reaction mixture will not become colorless because potassium
permanganate will remain, leaving the purple-pink solution.29 Therefore, the
concentration of potassium permanganate used was 0.005 mol.dm-3SK8 , which is very low so that the decolorization is efficient and distinguishable.
Despite the low concentration used, successful reaction will occur in this
case, because of the low volumes of reactants utilized due to the limited volumes
of the cuvettes used in the school lab (3.5cm3).

In this instance, the concentrations of the
reactants can be varied by changing the volumes of the reactants. Additionally,
distilled water should be used to maintain the surface area of the reaction
mixture, because changing the surface area impacts the rate of reaction.30 For sustainability
purposes, this method is favored because it involves less consumption of
resources to produce different solutions of the reactants at specific
concentrations to be used in the investigation.

The initial volumes of each reactant was
chosen to be 1.5cm3, as the volume of the cuvette is limited to
3.5cm3, and as the reaction with these volumes, from previous trials,
was seen to occur fast for repeats to be taken, and also slow enough for the
rate of reaction to be accurately derived. Furthermore, low volumes of potassium
permanganate will cause the color change to occur too fast. Therefore, volumes
of 0.5cm3 or higher were utilized. 1 mol.dm-3 was the
concentration chosen for ethanedioic acid, because higher concentrations cause
the rate of reaction to be too fast to follow.31 On the other hand,
successful trials can be achieved when using concentrations lower than this.
But considering the number of trials and repeats that should be carried out in
this investigation, the experimental process will be inefficient, due to the
slow reaction that will take place. Furthermore, the maximum time taken for the
reaction to be completed was found to be 6 minutes, and therefore the settings
of the data logger was chosen to collect data each 10 seconds for a period of 6
minutes.

Temperatures:
by doing trials, it was observed that 5°C is the lowest possible temperature provided
by the ice bath. Additionally, the temperatures at which the reactants
decompose are: 250oC for potassium permanganate32, and 189.5oC for
ethanedioic acid.33 These are impossible to
be achieved in a hot water bath. Therefore, there is no concern of the
reactants to decompose when choosing high temperatures. However, for the rate
of reaction to be accurately derived, the temperatures chosen should not be too
high, to prevent the reaction from being too fast to follow, as seen above in
the collision theory. To ?t the given information, 5 temperatures were chosen: 45°C,
35°C, 25°C, 15°C and 5°C.

Method to derive rate of reaction: the reaction reaches completion when the reaction mixture becomes
completely colorless, because this is an indication that the potassium
permanganate has completely reacted. Two methods are available to derive the
rate of reaction: a stop watch to determine the time required so that the color
change takes place, and colorimetry. In this investigation, colorimetry was used,
because when connecting colorimeters to the data logger interface, results are automatically
shown, so it is not needed to monitor the color change in the reaction mixture.
Further, it is subjective to decide when a color change had taken place, which
can possibly prevent accuracy and consistency in the data derived from the
experimental work. Hence, it is preferred to use colorimetry. Additionally, by
choosing colorimetry, multiple colorimeters, if possible, can be used simultaneously
reducing time-consumption when collecting data.

1 “Teenage
skin issues,” Clinuvel, accessed on Oct. 20, 2017, http://clinuvel.com/mothers-children-skin/childrens-skin/teenagers-13-17-years/teenage-skin-issues.

2 “Top
teen skin problem – and how to solve them,” WebMD, accessed on Oct 20,
2017, https://www.webmd.com/skin-problems-and-treatments/acne/features/top-teen-skin-problems-how-to-solve-them#1.

3 “Atopic
Dermatitis and Eczema”, Patient, accessed on Oct 20, 2017, https://patient.info/doctor/atopic-dermatitis-and-eczema.

4
Ibid.

5 “19th
WHO model list for essential medications,” WHO, published in Apr. 2015,
29, http://www.who.int/medicines/publications/essentialmedicines/EML2015_8-May-15.pdf.

6 “Activation
energy and temperature dependence of reaction rates,” Mhhe, accessed on
Oct. 20, 2017, http://www.mhhe.com/physsci/chemistry/chang7/ssg/chap13_4sg.html.

7
Ibid.

8
Jim Clark, “Energy profiles for simple reactions,” chemguide, last
updated on Oct. 2013, http://www.chemguide.co.uk/physical/basicrates/energyprofiles.html.

9 Jim Clark, “Orders
of reaction and rate equations,” chemguide, last updated Oct. 2013, http://www.chemguide.co.uk/physical/basicrates/orders.html.

10 “Lesson
3 Rate Law and Reaction Order,” Slideplayer, last updated 2016, http://slideplayer.com/slide/8124464/.

11
Jim Clark, “Orders of reaction and rate equations,” chemguide,
last updated Oct. 2013, http://www.chemguide.co.uk/physical/basicrates/orders.html.

12 Ibid.

13 Jim Clark, “Rate constants and the Arrhenius
equation,” chemguide, last updated Oct. 2013, http://www.chemguide.co.uk/physical/basicrates/arrhenius.html.

14 “Activation energy and temperature dependence of
reaction rates.” Mhhe. Accessed on Oct. 20, 2017. http://www.mhhe.com/physsci/chemistry/chang7/ssg/chap13_4sg.html.

15 Jim Clark, “Rate constants and the Arrhenius
equation.” chemguide. last updated Oct. 2013. http://www.chemguide.co.uk/physical/basicrates/arrhenius.html.

16 Ibid.

17
International Baccalaureate Organization. Diploma program. Chemistry Data
Booklet, last updated on Feb. 2014, 2, http://www.ibchem.com/root_pdf/data_booklet_2016.pdf.

18
“Oxalic acid,” Pubchem, accessed on Jan. 28, 2018, https://pubchem.ncbi.nlm.nih.gov/compound/971#section=Top.

19
Ibid.

20 Vanessa
Ngan and Staff Writer, “Potassium Permanganate,” DermNet
New Zealand, published in 2006, https://www.dermnetnz.org/topics/potassium-permanganate/.

21
Herbert Launer, “The kinetics of the reaction between potassium permanganate
and oxalic acid,” Journal of the American chemical society, published on
Jul. 1932, 2597. http://pubs.acs.org/doi/pdf/10.1021/ja01346a003.

22 Vanessa
Ngan and Staff Writer, “Potassium Permanganate,” DermNet
New Zealand, published in 2006, https://www.dermnetnz.org/topics/potassium-permanganate/.National Center
for Biotechnology Information. PubChem Compound Database; CID=516875,
https://pubchem.ncbi.nlm.nih.gov/compound/516875 (accessed Oct. 20,
2017).National Center for Biotechnology Information. PubChem Compound Database;
CID=516875, https://pubchem.ncbi.nlm.nih.gov/compound/516875 (accessed Oct. 20,
2017).National Center for Biotechnology Information. PubChem Compound Database;
CID=516875, https://pubchem.ncbi.nlm.nih.gov/compound/516875 (accessed Oct. 20,
2017).

23 “Oxalic acid,” Pubchem, accessed on Jan. 28,
2018, https://pubchem.ncbi.nlm.nih.gov/compound/971#section=Top.

24 “DEMONSTRATION:
reaction of oxalic acid,” Leek High School, accessed on Oct. 29, 2017, www.leekhigh.staffs.sch.uk/science/chemistry/Chim/RRfolder/RRD3.doc.

25 “Colorimeter,”
Vernier, accessed on Oct. 20, 2017, https://www.vernier.com/products/sensors/colorimeters/col-bta/.

26
Jim Clark, “The Beer-Lambert Law,” chemguide, last updated in May 2016, https://www.chemguide.co.uk/analysis/uvvisible/beerlambert.html.

27
International Baccalaureate Organization. Diploma program. Chemistry Data
Booklet, last updated on Feb. 2014, 15, http://www.ibchem.com/root_pdf/data_booklet_2016.pdf.  

28 “Investigating
the reaction between manganate(VII) and ethanedioate ions,” Royal Society of
Chemistry, accessed on Oct. 20, 2017, http://www.rsc.org/learn-chemistry/resource/res00002322/investigating-the-reaction-between-manganate-vii-and-ethanedioate-ions?cmpid=CMP00008124. 

29 “DEMONSTRATION:
reaction of oxalic acid,” Leek High School, accessed on Oct. 29, 2017, www.leekhigh.staffs.sch.uk/science/chemistry/Chim/RRfolder/RRD3.doc.

30
“Rate of reaction 3 – Explosions and catalysts,” BBC Bitesize, accessed
on Oct. 20, 2017, http://www.bbc.co.uk/schools/gcsebitesize/science/add_ocr_gateway/chemical_economics/reaction3rev1.shtml. 

31 “Speed
of reactions,” BBC Bitesize, accessed on Oct. 29, 2017, http://www.bbc.co.uk/bitesize/standard/chemistry/elementsandreactions/speed_of_reactions/revision/1/.

32 “The
thermal decomposition of potassium permanganate and related substances. Part I.
Chemical aspects,” The Royal Society of Chemistry, accessed on Oct. 29,
2017, http://pubs.rsc.org/en/Content/ArticleLanding/1971/J1/j19710001821#!divAbstract.

33
“Oxalic acid,” Pubchem, accessed on Jan. 28, 2018, https://pubchem.ncbi.nlm.nih.gov/compound/971#section=Top.

 SK1Is this a correct way of referencing figures? How to add the
reference within the textbox?

 SK2Is this a correct way of writing it?

 SK3What extra information to include about the acid?

 SK4What extra information do I have to add about potassium
permanganate?

 SK5Can I now mention reduction because I don’t have enough space to add
more information?

 SK6Is the explanation sufficient?

 SK7Is the explanation enough? Do I have to add anything else?

 SK8Is M the same as mol.dm-3?

x

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