ITEM
CONTENT
Objective
The purpose of this experiment is to synthesize potassium
tris(oxalato)chromium(III) trihydrate , K3[Cr(C2O4)3].3H2O .
Introduction
Synthesis is process in which substances combine to
form completely new substances .In this experiment we are
synthesizing coordination compound.Coordinatio compound
is the product of a lewis acid-base reaction in which neutral
molecules or anions bond to central metal by coordinate
covalent bonds.A coordinate covalent bond is a covalent
bond in which one atom supplies both electrons.This type of
bonding is different from a normal covalent bond in a bond in
which each atom supplies one electron.
Chromium(III) , the most stable oxidation state of
chromium , forms a number of complexes , in which six
monodentate ligands surround the cation octahedrally.There
is the balance chemical equation:
8H++3H2C2O4+6K2C2O4.H2O+K2Cr2O7
6CO2+9H2O+8K++2K3[Cr(C2O4)3].3H2O
In the above compound , two oxalate anions and two water
molecules coordinate the chromium cation to provide
oxygen atoms at the corners of the octahedron
The amount of coordination compound expected from a
given mass of reactants can be calculated and is called the
theoretical yield . The actual mass of coordination
compound synthesized , called the actual yield . The actual
MARKS
mass of coordination compound synthesized , called the
actual yield is usually less than the theoretical yield .
% yield= actual yield
x 100%
Theoretical yield
Results
8H++3H2C2O4+6K2C2O4.H2O+K2Cr2O7
6CO2+9H2O+8K++2K3[Cr(C2O4)3].3H2O
The number of moles H2C2O4 :
= 5.02720 / (2+24+64)
=0.05636 mol
The number of moles K2Cr2O7
=1.8740 / 294
=0.00637 mol
The limiting reactant is K2Cr2O7
1 mol of K2Cr2O7 = 2 mol of K3[Cr(C2O4)3].3H2O
0.0637 mol K2Cr2O7 = 0.01274 mol of K3[Cr(C2O4)3].3H2O
Molar mass of K3[Cr(C2O4)3].3H2O =487
The theoretical yield = 0.01274(487)
= 6.20438 g
Mass of K3[Cr(C2O4)3].3H2O obtained is 3.6887 g
Percentage yield of K3[Cr(C2O4)3].3H2O is
= 3.6887 g x 100%
6.20438 g
= 59.45 %
Discussion
In this experiment , we haves tudied how to synthesis
coordination compound . Coordination compound formed
when lewis acid that is cu2+ are reacted with lewis base that
is C2O4 and H2O.
Potassium dichromate , K2Cr2O7 dissoved slightly acid
solution , excess oxalic acid , H2C2O4 is added and the
following reactiion take place:
8H++3H2C2O4+6K2C2O4.H2O+K2Cr2O7
6CO2+9H2O+8K++2K3[Cr(C2O4)3].3H2O
Vigorouly orange solution was formed and filtered then
leaves for crystallization. Potassium oxalate , K2C2O4.H2O
was added . Dark green solution was formed and was
heated for five minutes.
After that we allowed the solution cool at room
temperature.The dark green crystal was was filtered and
washed with 1:1 ethanol/water and followed by 13 ml of
acetone. The mass of the dark green crystal obtained is
3.6887 g .The theoretical yield obtained is 6.20438 g.So the
percentage yield is 59.45 % .There is large different to
achieve 100% of theoretical yield.There maybe error occur
when we are doing an experiment.So there is some
precaution that we must take care while we are doing an
experiment .
First we need to makesure our conical flask is
cleaned before we are using it, this is important because
there maybe left other substance left in the conical flask and
cause our product was contaminated.We also need to
becareful when heating oxalic acid , potassium chromate
and potassium oxalate as it will bump when we heat too
long.
Conclusion
Potassium tri(oxalato)chromium(III)trihydrate ,
K3[Cr(C2O4)3].3H2O was synthesize.The actual mass
obtained was 3.6887 g while the theoretical yield obtained
was 6.20438 g . So the theoretical yield is 59.45 %
References
1) Duward F. Shiver , Inorganic syntheses , copyright
1979 , published by John Wiley & Sons, Inc. Page :
127
2) Raymond Chang and Kenneth A.Goldsby , Chemistry
, eleventh edition published by Mc Graw Hill copyright
2013 , page 103 and 104.