its a well described report on SYNTHESIS OF TRIS (THIOUREA) COPPER (I) SULPHATE and this serves to industrial chemistry students doing transition metal chemistry.

1. ©KWEZIJULIUS 12/U/494
MAKERERE UNIVERSITY
COLLEGE OF NATURAL SCIENCES
DEPARTMENT OF CHEMISTRY
CHM 2220/P
SYNTHESIS OF TRIS (THIOUREA) COPPER (I) SULPHATE
GROUP 9
NAME: KWEZI MWAKA JULIUS
REGESTRATIONNUMBER:12/U/494
STUDENT NUMBER:212000546
EXPERIEMENT3
COURSE INSTRUCTOR:MR. MULINDA STEVEN

2. ©KWEZIJULIUS 12/U/494
STABILISATION OF OXIDATION STATES
AIM: To synthesize Tris (thiourea) copper (I) sulphate
THEORY
When an element can exist in more than one oxidation state in aqueous solution, each oxidation
state will have different thermodynamic stability. In this experiment, an example of the
stabilization of an unusual oxidation state of copper was studied. The stability of Cu+, which is
generally less stable in comparison to Cu+ in aqueous solution, will be achieved by complex
formation using thiourea ligand that can function both as sigma-bond donor and π-bond acceptor.
It is to form stable complexes due to the neutrality principal.
Thiourea can coordinate to the metal via the sulphur atom.
16 Cu2+
(aq) + 8 (H2N)2CS(aq) + 16 H2O(l) 16Cu+
(aq) + S8(s) + 16 NH4
+
(aq) + 8CO2(g)
Cu+
(aq) + 3(H2N)2CS(aq) [Cu{(H2N)2CS}3]+
(aq)
The relative stability of the two oxidation states in aqueous solution is mostly expressed in terms
of the electrode potential for the reaction.
Cu2+ + (2-1)e- Cu+ where +2<+1
The electrode potential for a solution containing the ions, Cu2+ and Cu+ is given by the equation
𝐸0 +
𝑅𝑇
𝑍𝐹
ln⁡[[ 𝐶𝑢( 𝐼)]/[𝐶𝑢( 𝐼𝐼)]]
Therefore any species added to the solution which reduces the concentration of either Cu+ or
Cu2+ and so will alter the [Cu+/ Cu2+ ] will cause an observable change in the electrode potential.
If [Cu+] is reduced, then the observable potential will become more positive that is the higher
oxidation state will become more stable
Procedure
Apparatuses used
Burette, measuring cylinder, conical flask, beaker and the evaporating disc
Reactants used.
Sodium thiosulphate, Thiourea solution, copper sulphate solution, copper (II) pentahydrate,
distilled water, and starch indicatnor

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Thiourea solution was prepared by dissolving thiourea (2.5g) in water (15cm3), copper sulphate
solution was prepared by dissolving copper (II) pentahydrate (2.5g) in water (15cm3), thiourea
solution was prepared by dissolving thiourea (1.0g) in water (10cm3), thiourea solution was
prepared by dissolving thiourea (0.150g) in water (30cm3).
To the cold solution of thiourea was added a cold solution of copper (II) sulphate with constant
stirring. The solution was then left to stand for about ten minutes. When oil drops on the sides of
the beaker appeared, to this was added a cold solution of thiourea (thiourea (1.0g) in water
(10cm3)) and stirred vigorously to effect complete crystallization.
The reaction mixture was allowed to stand for five minutes and the white crystals were filtered
off. They were then recrystallized from a thiourea solution [thiourea (0.150g) in water (30cm3)
plus sulphric acid (5drops)] heated first to 750c and then cooled to form pure crystals. The
crystals were filtered and then washed with several portions of water (5cm3) and ethanol (5cm3)
RESULTS
Mass of the product
Mass of paper + product (g) 2.80
Mass of paper only (g) 0.91
Mass of the product (g) 1.89
Treatment of results
Equations of reaction are as shown below
Equation 1
16 Cu2+
(aq) + 8 (H2N)2CS(aq) + 16 H2O(l) 16Cu+
(aq) + S8(s) + 16 NH4
+
(aq) + 8CO2(g)
Equation 2
Cu+
(aq) + 3(H2N)2CS(aq) [Cu{(H2N)2CS}3]+
(aq)
RFM of thiourea
(H2N)2CS = 2(2+14)+12+32 = 76
Number of moles of thiurea = 2.5/ 76
= 0.0329 moles
RFM of CuSO4.5H2O = 64 + 32 +4×16 + 5(2+16) = 250
Number of moles of CuSO4.5H2O = 2.5/250 = 0.01 moles

4. ©KWEZIJULIUS 12/U/494
Calculation for the limiting reactant
Mole ratio CuSO4.5H2O : (H2N)2CS
0.01
16
:
0.0329
8
⁡
0.000625 : 0.0041125
Therefore the limiting reactant is copper (II) sulphate pentahydrate
From equation 1, mole ratio of Cu2+ to Cu+ is 16 : 16,
Moles of copper (I) produced is 0.01 moles.
From equation 2, mole ratio of Cu+ : complex is 1 : 1,
RFM of the complex,= [Cu{(H2N)2CS}3]2SO4
= [64 +3{(2+14)×2+12+32}×2+32+64]
=680
1 mole of the complex weighs 680g
But the moles of the complex produced equals moles of Cu+ in the reaction.
0.01 moles of the complex weigh (0.01 ×680)
= 6.8g
Percentage yield =
𝑎𝑐𝑡𝑢𝑎𝑙⁡𝑦𝑖𝑒𝑙𝑑
𝑡ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙⁡𝑦𝑖𝑒𝑙𝑑
× 100
= (1.89/6.8)×100
= 27.79412%

5. ©KWEZIJULIUS 12/U/494
COMPLEMENTARY EXERCISE
1.
Tests Observation Deduction
A solution of thiourea in dilute
hydrochloric acid was prepared
by dissolving thiourea (1g) in 1M
hydrochloric acid (10 cm3). To
this solution was added a little
copper powder and then warmed
gently
On addition of the copper
powder the solution turned
to brown and then turbid on
heating.
In presence of thiourea
copper powder reacts with
HCl to form [CuCl4]2- which
is brown
2. The structure of thiourea
S̈
C
H2N NH2
The sulphur atom is the one that binds to the metal. The electron that combine and form a bond
with the metal are the half filled p-orbital of sulphur and the lone pair of sulphur make the bond
Structure of the synthesized compound
SC(NH)2
(NH)2CS Cu SO4
SC(NH)2 2
3. Thiourea acts as a reducing agent
Mechanism for this reaction
2CS(NH2)2 (aq) [(H2N)2CuCS(NH2)2]2+
(aq) + 2H+
(aq)
4. Determination of the percentage of the copper in the product.
The product (0.5g) was decomposed with 50% (V/V) nitric acid (20 cm3) by carefully
evaporated to dryness.

6. ©KWEZIJULIUS 12/U/494
The solution was then left to cool and then the sides of the evaporating dish were washed with
water and the washing of the solution were transferred to a conical flask (250ml) and the solution
was diluted to about 50 cm3.
To this solution was added 2M aqueous ammonia solution until there was a faint blue precipitate.
The precipitate was dissolved in a minimum quantity of ethanoic acid and then 50% potassium
iodide solution (10 cm3) was added.
The liberated iodine was titrated with standard sodium thiosulphate (1M) solution using starch
indicator (1 ml)
Final burette reading (cm3) 15.00
Initial burette reading (cm3) 0.50
Volume of Na2S2O3 (cm3) 14.50
Treatment of the results
Nitric acid followed by heating decomposes and then oxidizes the Cu+ to Cu2+ , and the ammonia
solution reacts Cu2+ to form Cu(OH)2 which is dissolved in ethanoic acid.
Reaction during the titration
2Cu2+
(aq) + 4I-
(aq) Cu2I2(aq) + I2(aq)……………………equation 1
2S2O3
2-
(aq) + I2 (aq) S4O6
2-
(aq) + 2I-
(aq)………………………… equation 2
Moles of the I2(aq) that reacted with thiosulphate
1000 cm3 of the thiosulphate contains 0.1 moles
13.70 cm3 of the thiosulphate contains [(0.1)/(1000)]×14.50 =0.0014
From equation 2, mole ratio of S2O3
2- : I2 = 2 : 1
Therefore mole of iodine that reacted with thiosulphate = 1/2×(0.0014) = 0.0007moles
From equation 1,
1mole of iodine is liberated by 2 moles of Cu2+
0.0014 moles of iodine are liberated by 2×(0.0007) moles of Cu2+
= 0.0014moles of copper

7. ©KWEZIJULIUS 12/U/494
RFM of copper = 64
1mole of copper weighs 64g
0.0014 moles of copper weighs 0.0014×64 = 0.0896g
Percentage copper content =
𝑚𝑎𝑠𝑠⁡𝑜𝑓⁡𝑐𝑜𝑝𝑝𝑒𝑟
𝑚𝑎𝑠𝑠⁡𝑜𝑓⁡𝑡ℎ𝑒⁡⁡𝑝𝑟𝑜𝑑𝑢𝑐𝑡
× 100⁡
=⁡
0.0896
0.5
× 100
= 17.92%
Percentage content of the copper = 17.92%
5. Structure of the sulphur containing product
-ONa+ -ONa+
O=S S S S=O
O O
6. Copper (I) oxidation state can be stabilized by electrolysis. During the electrolysis the
concentration of copper (I) is oxidized to copper (II) that is the observable potential will become
more positive that is the higher oxidation state will become more stable.
7. Melting point.
Initial melting point (0c) 145
Final melting point (0c) 147
Average melting point (0c) 146
Discussion of results
The percentage of copper in the product was low (17.92%). The method used to determine mass
of the tris (Thiourea) copper (I) sulphate gave an actual (experimental) mass of 1.89g and the
theoretical mass was 6.80g. This led to a slightly lower percentage yield.

8. ©KWEZIJULIUS 12/U/494
Sources of errors
Buoyancy effect that caused errors in weighing
Some errors might have been due to poor cleaning of the apparatus
Loss of the mass of the product during washing and filtration
Parallax errors resulting into inaccurate reading of the burette
Overshooting the end point during the titration
Some mass was lost on the walls of the container
Recommendations
Should be very careful during the filtration and washing of the sample
Should avoid overshooting the end point by adding a drop of the titrant at a go
All glass wares should be cleaned thoroughly and distilled water should be used
While transferring the weighed reactants into the conical flasks and other apparatuses care must
be taken to avoid drop offs
Conclusion
This method of the stabilization of copper (I) oxidation state using Thiourea is highly
recommendable since it minimizes the errors that would arise from having very many ligands.
This is because Thiourea has the ability to act as a ligand as well as a reducing agent as shown
below
2CS(NH2)2 (aq) [(H2N)2CuCS(NH2)2]2+
(aq) + 2H+
(aq)

9. ©KWEZIJULIUS 12/U/494
References
1. Practical inorganic chemistry, (second edition) pages (78, 79) published by Chapman and
hall
2. A.J. Vogel, A text book of Quantitative Inorganic Analysis, 3rd edition, Longmans,
London, 1961. (or new editions).
3. B.A. El-Sayed and M.M. Sallam, Temperature and frequency dependent electrical
transport in thiourea and tris(thiourea) copper (I) sulphate, J. Mater. Sci.: Mater. Electron, 1999,
10, 63-66.