0. Republic of the Philippines
BATANGAS STATE UNIVERSITY
College of Engineering, Architecture and Fine Arts
www.batstateu-edu.ph Tel No. (043)425-0139 loc 118
CHEMICAL AND FOOD ENGINEERING DEPARTMENT
Experiment No. 3
SPECTROPHOTOMETRIC DETERMINATION OF
POTASSIUM PERMANGANATE
Jan Jericho C. Mentoy
ChE-2104
Professor:
Dave D. Ramos
Date:
December 6, 2021
I. INTRODUCTION
Spectrophotometry is an analytical method that determines the light absorption or the amount of
chemicals in an analyte by passing a light beam through it as each compound in the analyte
absorbs or transmits light over a certain wavelength. It is one of the most important method of
quantitative analysis in different fields such as physics, chemistry, chemical and material
engineering and clinical applications. It allows scientists and engineers to analyze various
samples without skin contact as the measurements are done directly in the sample container, a
Photopette, without having to transfer it.
Spectrophotometry utilize a spectrophotometer, an instrument that measures the amount of
photons(the intensity of light) absorbed after it passes through the analyte. As the instrument
measures the light’s intensity, the analyte concentration is determined. Depending on the range
of wavelength of the radiation source, a spectrophotometer could be classified into two types:
Ultraviolet-visible (UV/VIS) spectrophotometer and infrared spectrophotometer. An IR
spectrophotometer utilize light with a wavelength in the infrared range wavelength (700-15000
nm) of the electromagnetic spectrum. On the other hand, UV/VIS spectrophotometer utilize light
at the range of ultraviolet (185-400 nm) and visible (400 -700 nm) spectrum. The wavelength of
light within this range affect the excitation of electrons in the atomic or molecular ground state to
higher energy levels, inducing to an absorbance at wavelengths particular to each molecule.
In visible spectrophotometry, the transmission or absorption of a certain substance is identified
from the the observed color of a certain wavelength range. In theory, an analyte that absorbs
light with a wavelength that encompassess the visible light spectrum appear as black while an
analyte that transmits the visible light appears white. If an analyte absorbs red light at 700 nm
wavelength, it will show as green because green is the complementary color of red. Visible
spectrophotometers utilize a prism to specify a certain range of wavelength in order for the light
beam to passed through the analyte. As observed by the human eye, the wavelength could appear
as a specific color based on a certain range, as shown by the following table.
In this experiment, a UV/VIS spectrophotometry is conducted in order to determine the
concentration of an unknown potassium permanganate solution. A sample of stock solution from
potassium permanganate and distilled water was prepared and diluted to different concentrations
to formulate the different standard solutions. Then, the absorbance for each standard solution is
measured using a UV/VIS spectrophotometer. The data gathered for absorbance is plotted
together with the concentration of the solutions to formulate the calibration curve of potassium
permanganate. Finally, Beer’s law is performed to determine the compound’s molar absorptivity
and the unknown concentration of the potassium permanganate solution.
II. OBJECTIVE
The objectives of the following experiment are as follows:

To determine the concentration of the unknown analyte of potassium permanganate through
the calibration curve technique

To determine the calibration curve of the potassium permanganate solution

To investigate the maximum wavelength of potassium permanganate
III. THEORETICAL FRAMEWORK/RELATED LITERATURE
Ultraviolet-Visible Spectroscopy
Ultraviolet spectroscopy is an important analytical method that utilize light at the near infrared,
visible, and ultraviolet range of the electromagnetic spectrum. It is a fast, efficient and cost
effective technique that could be utilized to determine the concentration of the absorbing species
at fixed path length. The Ultraviolet-Vis spectrophotometer is an instrument utilized for UVVIS spectroscopy. It could be utilize to analyze liquids, gases, and solids by using radiative
energy corresponding to far and near ultraviolet, visible, and near infrared regions of
electromagnetic spectrum.
A light beam is passes through an analyte and the wavelength of light reaching the detector is
measured. The measured wavelength gives important imformation regarding the molecular
structure of the analyte and the number of molecules present in the intensity of the signal, giving
both qualitative and quantitative information. These information could be obtained as the
transmittance, absorbance or reflectance of radiation in 160 to 3500 nm wavelength range. When
the analyte absorbs the incident energy, the electrons of the molecule move to excited states or
the anti-bonding orbitals. For this transition to occur, the photon energy must match the energy
needed by the electron in order to moved to a higher energy state. This process encompasses the
basic principle of absorption spectroscopy.
When the light beam attraction increases, the analyte absorbance increases. This direct
relationship is shown by the Beer’s Law equation. When the molecules absorb the radiation at
specific wavelength, the absorption spectrum depicts the number of absorption band which
corresponds to the molecular structure of the analyte. As the electrons transition to an excited
state due to UV visible absorption, three types of electronic transition could occur:



transition involving ground state orbitals [σ (bonding) molecular orbital, π (bonding)
molecular orbital, and n (non-bonding) atomic orbital to anti-bonding orbitals[ σ* (sigma
star) orbital, π* (pi star) orbital];
transition involving charge transfer electron;
transition involving d and f electron.
Electronic transitions involve from the UV and visible light spectrum are σ to σ*, n to σ*, n to
π* , and π to π*. However, transitions from s to σ* and n to σ* are much energy intensive, thus
occurring in the far ultraviolet region. This results for saturated compounds to not exhibit
strong absorption in the ultraviolet region. On the other hand, transitions of the n to π* and π to
π* type occur in molecules with unsaturated center. Electronic transitions from these molecules
require less energy and occur at longer wavelengths compared to the transitions to σ* antibonding orbitals.
In spectroscopy, the molecular structure of the analyte affects the wavelength of maximum
absorption(λmax) and intensity of absorption When a molecular structure is modified, the ground
state to pi state electronic transition could occur on both the ultraviolet and visible region. Many
inorganic compounds in solution depict absorption in the visible region. These include salts of
elements with incomplete inner electron shells, specifically transition metals, as their ions are
complexed by hydration. Such absorption were derived from a charge-transfer process, wherein
visible light provides energy for electrons to move from one system to another. On the other
hand, in π to π * transitions, when occurring in isolated groups in a molecule, induce absorptions
at low intensity. However, the conjugation of unsaturated groups in a molecule affects the
absorption spectrum as the wavelength of maximum absorption becomes longer and the
absorption intensity increases. This effect could be observed in organic groups that contain n
groups that are conjugated with a π electron group such as ketones. Generally, the greater the
length of the conjugated system in molecule,the nearer the λmax comes to the visible region.
Transmittance
A photodetector in a UV/VIS spectrophotometer measures the intensity of light after it passes
through the analyte. This is labeled as transmitted intensity. The intensity of the transmitted light
is weakened by the analyte as it absorbs the light at specific wavelengths, thus lowering its value
compared to the original or incident intensity at the light source.
The ratio between the transmitted intensity (I) and incident intensity (Io) is defined as
transmittance . Transmittance is the main value determine by UV/VIS spectroscopy and is often
expressed as percentage
T= I
Io
From the value of transmittance, the absorbance of the analyte could be determined. It is defined
as the negative value of transmittance.
A=-log(T)
Lambert’s Beer Law
As the light passes through the transparent cuvette filled with the analyte, it’s intensity decreases
proportionally to the the analyte’s concentration. As the concentration of the solution becomes
higher, it will absorbs more light, thereby decreasing the transmitted intensity . Similar
relationship could be found in the length of cuvette and the attenuation of light, as a longer
cuvette will have a higher absorption of light.
These factors could be summarized by expressing the concentration and cuvette length as a
function of absorbance. In particular, the absorbance A is equal to the product of the extinction
coefficient ε, the concentration c and the path length d, as stated by the Lambert-Beer’s Law:
Wherein :



A=εxcxd
The sample concentration c is given in mol/L or g/mL, respectively
The path length d of the cuvette is given in cm,
The extinction coefficient ε (epsilon) is a sample specific constant describing how much the
sample is absorbing at a given wavelength (in L/(cm*mol) or mL/(cm*g), respectively).
When the path length is 1 cm and the concentration is 1% w/v, the extinction coefficient is
called specific absorbance (E1%1cm ). Through the Lambert-Beer’s Law, the concentration of the
analyte could be determined from the absorbance value as long as the path length d and the
extinction coefficient is ε known.
c= A
εxd
IV. MATERIALS AND METHODOLOGY


Reagent
- distilled water
- potassium permanganate ( KMnO4)
Equipment
- Erlenmeyer flasks ( 9 pcs )
- graduated cylinders
- Pipettes
- Beakers
- Volumetric Flask (100 mL)
- Wet Wipes
- Porcelain Spatula
- Aspirator
- Micropipette

PROCEDURE:
Preparation of Stock Solution
Prepare 1000 ppm of 100 ml solution of potassium permanganate starting with solid KMnO4
Use distilled or deionized water. The solution will be prepared in a 100-mL volumetric flask.
1.Determine the mass of potassium permanganate needed.
Calculation
g of KMnO4 = volume of solution x ppm = 100 mL x 1000 ppm = 0.1 g of KMnO4
106
106
2.Fill the volumetric flask approximately 75% full with water. Use a funnel.
3.Add the required potassium permanganate to the volumetric flask.
4.Stopper the volumetric flask and gently shake the solution.
5.After the potassium permanganate has dissolved, fill the volumetric flask to the
100-mL mark. Stopper the flask and gently shake the solution.
6.If necessary, adjust the volume of the solution to 100 mL using distilled water,
and shake again.
7.Label the volumetric flask.
Preparation of standard solution
From the stock solution, prepare five standard solution of sodium permanganate with varying
concentrations ( 0 ppm, 50 ppm, 75 ppm, 100 ppm & 250 ppm) by diluting it with distilled
water.
Preparation of the calibration curve
Place the cuvette with distilled water in the cell compartment and again set the absorbance to
zero. Measure and record the absorbance of each of the five standard solutions, starting with the
most dilute standard. After each measurement, rinse the cuvette with the next standard, not with
distilled water
Draw a plot having X-axis as concentration (ppm) and Y-axis as Absorbance at λmax (525 nm).
Use Beer’s law to calculate ε for KMnO4, given the cell width (path length l ) to be 1 cm.
Calculation of the Unknown Concentration of Potassium Permanganate
From the calibration curve of the standard solutions, determine the concentration of the unknown
KMnO4 by utilizing the formula for Beer’s Law.Through the Lambert-Beer’s Law, the
concentration of the analyte could be determined from the absorbance value as long as the path
length d and the extinction coefficient is ε known. The extinction coefficient depict the slope of
the calibration curve.
c= A
εxd
FLOWCHART
ILLUSTRATION

Preparation of stock solution
Determine the
amount of potassium
permangate needed
to prepare solution
Fill the volumetric Using a funnel, transfer the
flask with 75 % potassium permanganate to
the flask and gently shake
distilled water
the solution
Fill the volumetric flask again
with distilled water until it
reaches the 500 mL mark and
shake the solution.

Preparation of Standard Solutions and the Unknown

UV-Vis Spectrophotometer and Calibration Curve
V. PRESENTATION OF THE RESULTS
Presentation of Data Gathered from the Experiment
After conducting the experiment, the absorbance rate of the five standard solution in three
trials were recorded which is important in determining the calibration curve of concentration
against the absorbance. Moreover, the absorbace rate of the unknown concentration of potassium
permanganate is also measured.Along with the absorbance in the three trials, their average value
is also indicated.
Standards
(KMnO4)
0ppm
Trial 1
0
Absorbance
Trial 2
0
Average Absorbance
Trial 3
0
0
50ppm
0.849
0.845
0.851
0.848333
75ppm
1.188
1.188
1.182
1.186
100ppm
1.545
1.541
1.549
1.545
250ppm
3.799
3.809
3.789
3.799
Unknown
Sample
1.255
1.258
1.248
1.253666
Presentation of Calibration Curve Between the Concentration and Absorbance Value of
Potassium Permanganate

Calculation of the Regression Model
The linear regression line of concentration and absorbance is calculated wherein X is the
concentration of KMnO4 while Y is corresponding absorbance.
X
0
Y
0
x̄ - x
-95
y-ȳ
-1.4757
(x̄ - x)2
9025
(y-ȳ)2
2.1777
(x̄ - x)(y-ȳ)
140.1883
50
75
100
250
Mean(x̄ ) = 95
0.848333
1.186
1.545
3.799
Mean(ȳ)= 1.4757
-45
-20
5
155
-0.6273
-0.2897
0.06933
2.3233
2025
400
25
24025
SSx = 35500
0.3935
0.0839
0.00481
5.39772
SSy = 8.05763
28.23
5.7933
0.3467
360.1167
SPxy=534.675
Linear Regression Equation
Y= bx +a
b=SPxy / SSx = 534.675/ 35500 = 0.01506
a=ȳ-bx̄ = 1.4757 -(0.01506 x 95 ) = 0.04485
Linear Regression Equation : y = 0.01506x + 0.04485
Calculating R2
R2 = (
SPxy
)2 =(
534.675
)2 = (0.999705407)2 = 0.99941
√( SSx x SSy )
√( 35500 x 8.05763 )

Calculation of the Unknown Concentration Of Potassium Permanganate
Based on the calibration curve, the slope of the graph of concentration against the absorbance of
potassium permanganate is 0.01506, which equates to the molar absorbtivity . The path length
was 1 cm and the average absorbance was 1.253666. Through the Lambert-Beer’s Law, the
concentration is determined.
A= Ɛbc
C=
�
Ɛb
C=
1.253666
(0.01506 ���−1 ��−1 )(1��)
= 83.24475 ppm
Discussion
Ultraviolet-violet spectrophotometry is a common analytical method utilized to determine the
light absorption capacity or the concentration of an analyte by passing a light through it as each
compound in the analyte absorbs or transmits light over the visible and ultraviolet
electromagnetic spectrum. As the light passes through, it affects the excitation levels of the
electrons of the analyte in the atomic or molecular ground state to higher energy levels, inducing
to an absorbance at wavelengths particular to each molecule. This transmission or absorption s
identified from the the observed color of a certain wavelength range. In this experiment, the
absorbance and the maximum wavelength of the potassium permanganate solutions were
determined using a UV-Vis spectrophotometer and plotted in a calibration curve along with the
predetermined concentration. From the calibration curve, the concentration of the unknown
permanganate solution is identified. First, a 10 mL stock solution of 1000 ppm permanganate
was prepared using solid potassium permanganate and distilled water. By using the stock
solution , five standard solutions with varying concentrations (0 ppm, 50 ppm, 75 ppm, 100 ppm,
& 250 ppm) were prepared. In addition, the solution of unknown concentration was also
prepared from the stock solution.
After the preparation, a UV-Vis spectrophotometer was utilized to determined the maximum
wavelength of potassium permanganate and the absorbance of the standard solutions . The
maximum wavelength of the potassium permanganate obtained was 525 nm. After determining
the maximum wavelength, the absorbance for each standard solution was measured. For the 0
ppm concentration, the average absorbance obtained was 0. The average absorbance of 50 ppm
solution is 0.84833. The 75 ppm solution indicated an absorbance of 1.186. An average
absorbance of 1.545 was obtained from the 100 ppm solution. For 250 ppm, the absorbance
was 3.799. Moreover, the average absorbance of the unknown standard solution was also
measured with a value of 1.4757. These values along with their respective concentration were
plotted in a calibration curve giving a linear exponential line. The equation from the linear
exponential line is y = 0.01506x + 0.04485 with a slope of 0.01506, which represents the molar
absorbtivity(�) of the potassium permanganate. From this value along with the path length(b) of
1 cm and the absorbance(A) of 1.4757, Lambert-Beer’s Law is applied with a formula of
A=��� to calculated the concentration of unknown. The concentration value of the unknown is
83.24475 ppm.
Furthermore, the graph showed the R2which represents the correlation coefficient value.
Correlation coefficient value is the statistical measure of the degree that indicates the variation of
a dependent variable in regards by the independent variable(s) in a regression model.The
correlation coefficient varies about +1 to -1. The graph showed a correlation efficient value of
0.9994, which is closest to +1. This indicates the values are close to the indicated regression line,
which depicts the accuracy of the gathered data.
VI. CONCLUSION
The experiment is conducted to determine the calibration curve of the standard solutions
and to determine the concentration of the unknown solution of potassium permanganate. A 100
mL stock solution of 1000 ppm was prepared and utilized to prepare five standard solution of 0
ppm, 50 ppm, 75 ppm, 100 ppm, & 250 ppm concentration and unknown concentration.
Through a UV-Vis spectrophotometer, the absorbance of the solutions were determined. The
average absorbance of the solutions were 0(0ppm), 0.848333(50ppm), 1.186(75 ppm),
1.545(100 ppm), 3.799 (250 ppm), and 1.25366 (unknown). These values were plotted in a
calibration curve, which resulted in a linear exponential line with an equation of y = 0.01506x +
0.04485 and a slope of 0.0156. It has a correlation coefficient of 0.9994, depicting the closeness
of values to the linear regression mode. Moreover, through the Beer’s Law, the concentration of
the unknown potassium permanganate was determine which was 83.24475 ppm.
VII. REFERENCES
[1]. L.E. Laverman. (n.d).Experiments in Analytical, Physical and Inorganic Chemistry – 3rd
Edition. Retrieved date by 15 July 2014.
[2]. Skoog, Douglas A., West, Donald M., Holler, F. James, Crouch, Stanley
R.. (2014). Fundamentals of Analytical Chemistry (Ed. 9th). Singapore: Cengage Learning.
[3]. Robert Bohman. (2006). Ultraviolet/Visible (UV-Vis) Spectroscopy of Potassium
Permanganate. Retrieved date by 15 July 2014.
[4]. Pavia, D. L., Lampman, G. M., & Kriz, G. S. (1979). Introduction to spectroscopy: A guide
for students of organic chemistry. Philadelphia: W.B. Saunders Co.
\
VIII. DOCUMENTATION
Image 1,2,&3 : Preparation of Stock Solution
Image 4, 5,& 6 : Preparation of Standard Solutions and Unknown
Image 7, 8,& 9 : Determining Absorbance through UV-Vis spectrophotometer