SCHOOL OF NATURAL AND APPLIED SCIENCES
DEPARTMENT OF CHEMISTRY AND CHEMICAL ENGINEERING
TO : MISS. M CHIWAULA
FROM : BLANDINA KIPANDULA
REG NUMBER : BSC-CHE-HON-48-23
EXPERIMENT TITLE DETERMINATION OF THE FORMULA OF THE
COPPER (II)/1,2-DIAMINOETHANE COMPLEX BY
COLORIMETRY
COURSE CODE : CHE 222
DUE DATE :22ND APRIL 2025.
ABSTRACT
The purpose of this experiment was to determine the formula for the coordination complex
formed between copper(II)/1,2-diaminoethane ions with equal concentrations of 0.05M and their
formula was determined to be [Cu(H2NCH2CH2NH2)2]+2 , different intervals of volume were
added respectively in order to find the best volume fit for the formation of the complex
compound. The oxidation number for copper was calculated to be +2. The stoichiometric ratio of
the reaction was 1:2, the maximum absorbance was reached at a volume of 8 cm3 of copper
suphate and 4 cm3 of 1,2-diaminoethane, with the test tube having a deep blue color with a
wavelength of approximately 400 nm. The maximum was obtained by interpreting the peak of
the graph and by noting which test tube had the thickest color and test tube had 5 had the
maximum color intensity of indigo, a deep blue color was shown in test tube 6 with an
absorbance of 0.415.
INTRODUCTION
This experiment made use of a 0.05M copper sulfate solution. copper is a transition metal and it
typically behaves like metals, possessing metallic luster and relatively high electrical and thermal
conductivities. Silver is the best conductor of heat and electric current, followed by copper.
Transition metal ions, when surrounded by a certain number of ligands they form cations called
complex ions (Zumdahl, 2014). Ligands are molecules or ions that behave as Lewis bases and
they surround a metal in a complex ion (Chang, 2010), 1,2-diaminoethane is a ligand in this
experiment, and it was mixed with copper sulfate, resulting into a compound called a
coordination compound since it consists of a complex ion and a counter ion. The coordination
number is defined as the number of donor atoms surrounding the central atom in a complex ion
(Chang, 2010). Complex ion in this case is a highly colored ion, and assuming that the maximum
color intensity coincides with a maximum number of complex ions formed.
One can determine the formula for the coordination compound using titration and calorimetry
methods. calorimetric methods require measurements of color intensity of the mixture as the
proportion of metal ion to ligand is varied, while titration involves competitive complexing.
When copper ion reacts with 1,2-diaminoethane, a deeply colored complex is produced. The
reaction equation is written as
Cu2+ (aq) + xH2NCH2CH2NH2 (aq [Cu (H2NCH2CH2NH2) x] 2+ (aq)
As for the value of X, this experiment aimed at determining the value of x.
Absorbance is measured on an instrument named UV-VIS spectroscopy,
which provides insight into the electronic transitions of the complex, enabling
determination of its composition by analyzing absorbance changes as a
function of ligand to metal mole ratio ( Perkameus, 2010).
METHODOLOGY
Nine test tubes were numbered from 1 to 9, and using these test tubes, mixtures of 0.05M CuSO₄
and 0.05M 1, 2-diaminoethane with compositions as in the table below (each with 12 cm³) were
made. The test tubes were shaken thoroughly to ensure the homogeneity of the mixture.
TEST TUBE NUMBERS 1 2 3 4 5 6 7 8 9
VOLUME OF 0 2 3 4 6 8 9 10 12
CuSO4(cm3)
VOLUME OF 1,2- 12 10 9 8 6 4 3 2 0
DIAMINOETHANE(cm3)
We then went to another lab to measure the absorption of the solutions in the test tubes. Then
each test tube was placed in a cuvette, which was then placed in UV-VIS. The cuvette was
cleaned with distilled water, and the solution to be tested was added to it. Tissues were used to
erase fingerprints so that they could not be detected. Results were recorded in a table.
RESULTS AND DISCUSSION
Test tube number 1 2 3 4 5 6 7 8 9
Volume of 0 2 3 4 6 8 9 10 12
CuSO(cm3)
Volume of 1,2- 12 10 9 8 6 4 3 2 0
diaminiethane(c
m3)
Absorbance 0 0.009 0.061 0.027 0.046 0.415 0.195 0.237 -0.003
Color of solution Trans Light Purpl purpl Deep Violet blue Pale blue Clear
paren blue e e blue blue
t
Below is graph showing absobance against volume of solution of CuSO4 and 1,2-diaminoethane
Absorbance VS Volume of CuSO4
0.45
0.4
0.35
0.3
absorbnace
0.25
0.2
0.15
0.1
0.05
0
0 2 4 6 8 10 12 14
-0.05
volume of CuSO4(mL)
The wave length of the UV-VIS spectrophometer was 400nm.
DISCUSSION
From the graph it shows the absorbance was at 0.415 at volumes of 8 mL and 4 mL with deep
blue color. Absorbance is a measure of how much light is absorbed by a sample( Atkins, 2014).
It is defined as:
A=concentration X length X molar absorptivity
This formula will help in finding concentration of the complex ion, mostly length is said to be 1
cm. This experiment also had errors that were involved, such as: improper dilution, cuvette
contamination or baseline calibration, and inconsistent mixing or concentration errors when
preparing the solutions. To obtain more accurate results there is need to reduce the occurrence of
such errors, this can be done by performing UV-VIS scans per sample more than just one time to
ensure reproductivity and also well calibration of burette to titrate correct amounts of titrant.
CONCLUSION
In conclusion, the 0.415 with a deep blue color showed and had the highest absorbance at
volume of 8 and 4 mL. The oxidation number for copper was calculated to be +2 with the
reaction having a stoichiometric ratio of 1:2, The formula was found to be:
[Cu(H2NCH2CH2NH2)2]+
Therefore, the experiment was a success and for a given ligand, the color depends on the
oxidation state of the metal ion (Silberberg, 2007), and for a given metal ion color depends on
the ligand; even a single ligand substitution can have a major effect on wavelength. The
determined formula suggest that copper(II) coordinates two 1,2-diaminoethane ligands forming a
square planar or octahedral complex, the titration results align with a ratio of 1:2 and it was
consistent with the bidentate nature of 1,2-diaminoethane.
REFERENCES
Atkins,p.& de paula,j.(2014).Physical chemistry. Oxford university press.
Chang,R.(2010).Chemistry.(10th ed). McGraw-Hill: New York
Perkampus,H.(2012).UV-VIS Spectroscopy and its application.Germany:Springer Berlin
Heidelberg.
Silberberg,M.S.(2007).Principles of General chemistry.McGraw-Hill:New York.
Zumdahl,S.S.(2014).Chemistry.( 9th ed).Mary Finch: United States.
APPENDIX
Colorimetry is an analytical technique used to determine the concentration of a colored substance
in a solution by measuring the intensity of light absorbed or transmitted at a specific wavelength.
It is based on the Beer-Lambert Law, which relates the absorption of light to the concentration
of the absorbing species, the path length of the light, and the substance's molar absorptivity.
Beer-Lambert Law
A=ϵ⋅c⋅l
┌──────────────┐ ┌────────────┐ ┌────────────┐
┌────────────┐
│ Light Bulb │ ---> │ Filter │ ---> │ Cuvette │ ---> │ Detector │ ---> Absorbance
Reading
└──────────────┘ └────────────┘ └────────────┘
└────────────┘
(Emits light) (Selects λ) (Holds sample) (Measures I)
2.The color of the complex ion was deep blue
3.400 nm was most suitable since it was were the maximum absorbance was observed and it was
the highest peak on the graph
5.The volumes where at 6 cm3 for both CuSO4 and 1,2-diaminoethane solutions
6.concetration of copper sulphate= 0.05 M and same for 1,2-diaminoethane
Volume for copper sulphate= 8cm3
Number of moles for CuSO4= 0.05 X 8x10^-3=0.0004 mols
Number of mols for 1,2-diaminoethane=0.05 X 4x10^-3=0.0002 mols that is the molar
proportions must be 1:2
7.Cu2+(aq) + 2H2NCH2CH2NH2(aq) [Cu(H2NHCH2CH2NH2)2](aq)
NH3
H3 N Cu +2 NH3
NH3
The difference is that from the complex ion ligand uses up two positions at
right angle to each other as chelating agent having the ability to hold a
metal atom like a craw while [Cu(NH3)4]2+ is just one ligand surrounding the
metal atom one per position.
9. A. Given CuSO4. H2O, assay = 99%
To prepare a 100ml 0.05M CuSO4
N = CV = 0.05M x 0.1L = 0.005moles
Mass = n x RFM (CuSO4. H2O) = 0.005moles x 244.64g/moles= 1.2484g
Therefore, measuring 1.2 grams of CuSO4. H2O and add distilled water to
100ml mark.
B.1, 2-diaminoethane assay = 99%,
Actual mass assay=1.2484 g/ 0.99= 1.261 g
To prepare 100 mL of 0.05 1,2-diaminoethane
Density 0.9gml-1
Mass 60.10gml-1
Volume= 0.1 L
Desired concentration= 0.05 M
Moles = CV= 0.05 X 0.1= 0.005 mol
Mass of pure 1,2-diaminoethane needed
Mass= 0.005X60.10= 0.3005 g
Adjust assay( 99 % purity)
Actual mass = mass/assay= 0.3005/0.99= 0.3035 g
Volume of 1,2-diaminethane
Density=mass/volume
Volume= 0.3035/0.9= 0.3373 mL
Summary of requirements
CuSO4 1.261 g of CuSO4·5H2O, dissolve in distilled water, and dilute to 100 mL.
1,2-Diaminoethane solution Measure 0.337 mL of 1,2-diaminoethane, add to distilled water,
and dilute to 100 mL.
