Synthesis of a Cobalt-AmineHalide Compound
Keelie Bolton
Chemistry 1212
Dr. Laroui
12-9-13
Desk #J-42
Synthesis Number 5
II. Introduction
The primary objective for this lab is to perform accurate chemical analyses for the
quantity of elements and compounds in a sample. The purpose of the experiments is to
synthesize a colored, metal-containing compound, perform accurate quantitative analyses to
determine and confirm the composition of the synthesized product, and determine a possible
formula of the synthesized product. The synthesized product is a Cobalt Amine-Halide product
with a coordinate covalent bond. Unlike simple covalent bonds where two atoms share electrons
that are attracted by both nuclei, a coordinate covalent bond occurs when both electrons come
from the same atom. These special covalent bonds may be found in reactions between ammonia
and hydrogen, or when a Lewis base donates electrons to a Lewis acid. In diagrams, these
coordinate covalent bonds are represented by an arrow pointing from the atom donating the lone
pair to the atom accepting it.
III. Procedure
1. Synthesis Procedure V
In this experiment, preparation of the Cobalt-Amine-Bromine product was
performed by synthesis procedure V in the lab manual. This consisted of placing 4 grams
of the unknown cobalt(III) compound into a solution of 15ml 9M hydrobromic acid and
10 ml of water.7g of NH4Cl and 35 ml concentrated aqueous ammonia were added to the
solution. 7ml of 30% hydrogen peroxide was added and the whole solution was heated on
a hotplate. 50ml of 4.5M HBr was then added and the mixture was heated again. The end
result, after suctioning the precipitate, was 8.0 grams of a purple, chalky compound.
The Cobalt-Amine-Halide will have a general formula of
[Co(NH3)x(H2O)x]Brx
(where the large X may or may not be present and could possibly be Br)
2. Determination of %Bromine
For the determination of percent Bromine in the synthesized compound, 1.74g of
silver nitrate (AgNO3) solution was dissolved in 50ml of d.i. water and 10 drops of
HNo3 was added. Next, two samples of the synthesized compound (one 0.2474g and
the other 0.2428g) were obtained and transferred into two clean beakers, and then
dissolved by adding approximately 130 milliliters of deionized water and 10 drops of
concentrated HNO3 to each beaker. Finally, 25 milliliters of the prepared AgNO3
solution were added to each beaker and boiled for 45 minutes. The AgCl precipitate
from each beaker was collectible in two separate Gooch crucibles.
3. Preparation and Standardization of an HCl solution
In order to perform the analysis of percent ammonia (NH3) in the cobolt(II)
compound, 500 milliliters of approximately 0.3 molar hydrochloric acid solution
(HCl) was prepared and standardized. It was standardized in triplicate by titrating the
HCl with 0.8000-1.1000 g of THAM dissolved in 90ml of water. 4 drops of bromcresol-green indicator was added to each titration. In the first titration, 0.91g of
THAM was used and it took 26.40ml of HCl to reach the endpoint which had a
yellowy color. In the second titration 0.91g of THAM was also used. It took 26.00ml
of HCl to reach an endpoint of a light green color. The last titration was performed
using 0.91g of product and titrated with 26.20ml of HCl to a light green endpoint.
(HOCH2)3 CNH2 + HCl  (HOCH2)3 CNH3+ + Cl-
4. Determination of % Ammonia
For this experiment, percentage of ammonia (NH3) was also done in triplicate.
2.0 grams of boric acid were placed into three flasks and each were dissolved in
approximately 5o milliliters of deionized water and cooled to room temperature. Next, a
distillation apparatus was set up and three samples were obtained (0.3707g in the first
sample, 0.4034g in the second sample, and 0.3594g in the third sample). One of the
samples was placed in the round bottom flask along with 50 milliliters of 9 molar NaOH
solution and NH3 was distilled into the flask containing boric acid through heating and
cooling. Four drops of indicator was added to each sample and then each was titrated
with the approximately 0.3M HCl. The first flask reached its endpoint after 12.60
milliliters of HCl was added and it was a green-blue color. The second flask reached its
endpoint after 11.00 milliliters of HCl and also had a similar green-blue color. The third
flask was a green-blue color after reaching its endpoint with 10.40 milliliters of HCl.
5. Preparation and Standardization of a 0.1 M Thiosulfate solution
To determine the percent cobalt in the synthesized compound, a 500 milliliter, 0.1
M solution of thiosulfate solution was prepared and then standardized to determine its
average molarity. In the first trial, 0.1119g of KIO3 was placed into a flask with about 72
milliliters of d.i. water. Three grams of KI and 3ml of 6M HCl were also added and the
solution was titrated with the approximately 0.1M Na2S2O3. A starch indicator was used
and the first sample reached its endpoint after 30.40 milliliters and it was a clear color. In
the second trial, 0.1054g of KIO3 was titrated with 30.40 milliliters of thiosulfate to a
clear color. The last trial contained 0.1015g or KIO3 titrated with 22.60 milliliters of
thiosulfate to a clear color.
PREPARATION STEP:
IO3- + 6H+ + 5I-  3I2 + 3H2O
TITRATION STEP:
3(I2 + 2S2O32-  2I- + S4O62- )
3I2 + 6S2O32-  6I- + 3S4O6
COMBINED STEPS:
1IO3- + 6H+ + 6S2O32-  I- + 3S4O62- + 3H2O
+3
6. Determination of % Cobalt (Co ):
The analysis for percent cobalt in the synthesized compound was done in
triplicate. Three samples of the synthesized compound (0.5070g, 0.5251g, and 0.5031g)
were obtained, and placed into three different flasks. Next, 35 milliliters of deionized
water and 10 milliliters of 50% NaOH were added to each of the three flasks and then
heated strongly for approximately 20 minutes. The flasks were then cooled to room
temperature and 2 grams of KI was added to each flask. Finally, 40 milliliters of 6M HCl
was added to one of the flasks and immediately titrated with 5 milliliters of the starch
indicator after noting the red-brown acidic color change. In the first sample 13.6
milliliters of thiosulfate was required to reach the endpoint of a light pink color. The
second sample required 12.2 milliliters of thiosulfate and appeared a light pink/purple.
The last sample took 12.5 milliliters to titrate to reach the light pink endpoint.
PREPARATION STEP:
2Co3+ + 2I-  2Co2+ + I2
TITRATION STEP:
I2 + S2O32- +  2I- + S4O62COMBINED STEPS:
2Co3+ + 2S2O32-  2Co2+ + S4O62-
IV. Data and Calculations
Table #1 Weight of Empty Crucible
Date
Crucible #1
1-20-12
30.8035g
1-27
30.8034g
Best Average
30.8034g
Average weight of crucible example calculation:
30.8035+30.8034=
Table #3 Determining Molarity of HCl
Color at endpoint
Yellowish
G THAM
0.91g
Initial vol. HCl
0.00ml
Final vol. HCl
26.4ml
Vol HCl (initial-final) 26.40ml
Mol THAM
0.0075
Mol HCl
0.0075
M HCl
0.2845M
Table #3 continued
Average M HCl
Average deviation
% deviation
Crucible #2
30.4386g
30.4383g
30.4383g
Light green
0.91g
20.00ml
46.00ml
26.00ml
0.0075
0.0075
0.2889M
Green
0.91g
19.9ml
46.10ml
26.20ml
0.0075
0.0075
0.2867M
0.2867M
0.0018
0.62783%
Table #4 Determination of percent Halide
CoInitial
Final weight
compound
weight of
w/precipitate
(g)
crucible (g)
(g)
Sample 1
0.2474
30.8034
31.1328
Sample 2
0.2428
30.4384
30.7874
Average % Deviation=7.88%
Average %-58.84% Br-
Weight of
precipitate
(g)
0.3287
0.3491
% Br
% deviation
56.52
61.16
± 2.32
± 2.32
Table #5 Standardization of HCl
Co-compound Initial volume of
(g)
HCl (L)
Trial 2
0.4034
0.0010
Trial 3
0.3594
0.0130
Average % Deviation-2.98
Average %-13.73% NH3
Table #6 Standardization of Thiosulfate
KIO3 (g)
Initial volume of
Na2S2O3 (L)
Trial 1
0.1119
0.0076
Trial 2
0.1054
0.0000
Trial 3
0.1015
0.0096
Average molarity-0.1012 M Na2S2O3
Final Volume
of HCL (L)
0.0120
0.0234
Endpoint (L)
% NH3
0.0110
0.0104
Final volume of
Na2S2O3 (L)
0.0380
0.0304
0.0372
Endpoint
(L)
0.0304
0.0304
0.0276
Data table #7 Thiosulfate titration
G Cox
Ml NaOH G KI
0.5070
10.00
2.1
Ml HCl
40.00
Initial vol
1.00
Final vol
14.60
ml thiosul.
0.5251
10.00
2.2
40.00
15.00
27.20
12.20
0.5031
10.00
2.1
40.00
28.00
40.50
12.50
Data table #8 Analysis of %Co3
M Na2S2O3
1
0.1012
2
0.1012
3
0.1012
Average % Co= 14.89%
Deviation Co=
Average Deviation=
% Deviation
molCo
0.0014
0.0012
0.0013
G Co
0.0811
0.0728
0.0745
13.60
%Co
15.99
13.86
14.82
% deviation
30.65
30.10
Molarity
(mol/L)
0.1032
0.0972
0.1031
Sol. color
Light
pink
Light
pink
Light
pink
±0.4970
±0.0270
V. Results/ Analysis
1. Synthesis
Performing the synthesis number five procedure yieldied eight grams of a chalky purple
compound. 8.00 grams of product seemed to be a sufficient amount to utilize in the following
experiments to determine the formula of the Cobalt sample.
2. Determination of % halide
The best average percent Bromine achieved through this experiment was 58.84% with a 3.94%
deviation. This deviation is a little high and will be a slightly unreliable when identifying the
formula of the Cobalt sample. This deviation could have been high as a result of inaccurate
measurements when the crucibles were weighed. For example, oil from fingerprints could distort
the readings on the analytical balance causing higher weights that are more separate from each
other causing a higher deviation.
3. Standardization of HCl solution
The average molarity of the HCl solution that was prepared is 0.2867% with an average
deviation of 0.0018. These numbers appear to be favorable since the deviation is a low number
and the average molarity is close to the approximate 0.3% HCl that was meant to be prepared.
4. Determination of % Ammonia
Several mistakes were made during this experiment. For example, in the second trial 0.4034g of
product was used which was not in the 0.3000-0.4000 range that was meant to be followed. This
discrepancy could have contributed to the high percent deviation that was first taken to be
8.57%. Because this number was so high, Trial number 1 is removed from the calculations
because it diverges the most from the other two. After trial 1 is removed, the new percent
deviation is 2.98% and the overall average % ammonia is 13.73%. A new percent deviation o f
2.98% is a more trustable number to use when determining the formula of the cobalt sample.
5. Standardization of thiosulfate solution
Through this procedure, it is discovered that the best average value for the molarity of the
Na2S2O3 solution that was prepared is 0.1012M with a percent deviation of 2.60%. This value
may be a little high, but it is believed that it is still a trustworthy number to use in the
identification of the cobalt compound. Perhaps titrating too far on the first titration could have
caused the higher reported deviation.
6. Determination of % Cobalt
The overall percent Co found on average through this experiment is 14.89% with a percent
deviation of 4.93%. This number (the deviation) is a little high. It would be used in the
identification of the Cobalt sample with, in mind, that it is not the most trustworthy number. The
deviation may be high because of inaccurate measurements of NaOH. Dilution factors may have
been miscalculated when trying to reach the 50% NaOH solution causing a higher deviation.
VI Discussion
The final percents of compounds listed out are as follows:
%Br – 58.84%
%NH3 – 13.73%
%CO – 14.89%
%H2O – 12.54%
The final molecular formula is believed to be : Co(NH3)3(H2O)3Br3
Theoretically, the % Br and the % H2O would have been a little higher, the %NH3 would be a
little lower.
VII Conclusion
After performing many chemical analysis’ on the same cobalt(II) compound the concluded
formula for the synthesized compound is [Co(NH3)3(H2O)3]Br3. The actual empiral formula obtained
is [Co(NH3)3.19(H2O)2.75]Br2.91. This formula was chosen on the basis that it is the closest to the
formula obtained from the lab itself. It is extremely hard to acquire a formula exactly the same as the
ones listed in the manual. And through process of elimination, first comparing the values with the
lowest percent deviations to the ones on the chart, working all the way to those with larger
deviations, this formula is the only one suitable for the results obtained from the various experiments.
The final percents are 58.84%Br, 13.73%NH3, 14.89%Co, and12.54%H2O. The other formula which
could possibly close to these percents is [Co(NH3)4(H2O)2]Br3. This formula is close because of the
values of 14.64%Co and 59.93%Br which are close to those obtained from experimentation.
However, this formula is ruled out because of the 16.89%NH3 which is very far away from the
13.73%NH3 reported from the experiment. No other formulas are as close to the experimental results
as these two are and since [Co(NH3)4(H2O)2]Br3 is ruled out as the formula for the compound being
observed, [Co(NH3)3(H2O)3]Br3 has to be the formula for the cobalt compound made using synthesis
procedure V according to these results.