Chris Mozdzen
Lab Paper
Intro
In this experiment the purpose was to determine the empirical formula of
KxFe(C2O4)y*zH2O using the synthesis of a complex iron crystal with
the reaction
FeCl3(aq)+K2C2O4(aq)+H2O(l)-> KxFe(C2O4)y*zH2O+ junk, with junk being unnecessary molecules
and parts that do not need to be calculated in the empirical formula. In the following experiments
the other components of the crystal such as Oxalate, Potassium, Iron, and water ions were
determined utilizing redox reactions, acid-base reactions, titrations, dehydration and other
processes. The formula for these components was xK+(aq)+Fe3+(aq)+yC2O42-(aq)+zH2O>KxFe(C2O4)y*zH2O(s).
Procedures
First, 24.0 g of Potassium Oxalate was added to RO water and was heated once dissolved,
16.0 mL of Iron (III) Chloride was added to the solution. This was cooled for about for about 1.5
hours to allow the formation of crystals. Once formed, the crystals were crushed and reheated in
water until dissolved to be placed in a bin for a week. These resulting crystals were vacuumed to
remove the extra moisture and rinsed with acetone and weighed before the dehydration process.
For dehydration, a proper sample size of 1.0- 1.2g of crystals was spread on the bottom of
three labeled beakers and heated for about an hour at 120 degrees. They were then cooled and
weighed, reheated for 30 minutes, to ensure all water had been removed, and weighed a final
time to determine the percent of water in the iron salt.
To find the percent by mass of K+ and Fe3+ inside of the iron salt (KxFe(C2O4)y*zH2O) a
titration reaction was conducted. 0.3 grams of the iron salt was dissolved in a beaker with RO
water and sent through an ion exchange column to isolate the K+. Once that was finished, a stir
bar was put into the iron salt solution and placed on the mixing plate under a buret. The iron salt
solution was titrated using NaOH, a calibrated electrode calculated and graphed the pH values of
the solution during the tritration and precipitation of the solution.
For the second titration the purpose was to determine the percent of C2O4 in the iron salt.
Approximately 0.15g of the iron salt was added to an Erlenmeyer flask along with 5.0mL of 20%
phosphoric acid, RO water and 15 mL of 2M sulfuric acid; this solution was the heated and
stirred until the iron salt dissolved. 02 M KMnO4 was used as the titrant and the iron salt solution
was titrated until a light pink color was observed without fading. The final volume was recorded
and more trials were conducted as necessary.
RESULTS
Synthesis Data
Mass of K2C2O4 used (g)
Mass of Iron Salt formed (g)
Observations
Percent by Mass of Water Data
Trial 1
Mass Empty Beaker
8.456
Mass Beaker and
9.519
Sample
Mass of Sample
1.063
st
Mass after 1 Heating
1.019
24.511
12.706
Green crystals formed
slowly; looked like
layers
Trial 2
8.671
9.866
Trial 3
8.552
9.653
1.195
1.150
1.101
1.055
Mass after 2nd Heating
1.009
1.142
1.045
Mass of Water Lost
.054
.053
.056
% H2O
5.07
4.44
5.09
Median %H2O:5.07
Range:0.65
Relative % Range:12.82
SHOW CALCULATIONS – Note show the calcs for just one trial. Do not take up more than two lines
worth of space
Trial 1: 9.519g-8.456g=1.063g-1.009g=(.054g/1.063)*100=5.07%
Percent by Mass of K and Fe Data
Trial 1 Trial 2
Mass of Sample
.296
.296
Molarity of NaOH
.2061
.2061
Volume of 1st EQ. pnt
8.23
8.98 mL
mL
Volume of 2nd EQ. pnt
8.73mL 10.01mL
%K
22.5
24.4
% Fe
10.8
13.0
Median %K:23.5
Median %Fe:11.9
Range of %K: 1.9
Range of %Fe:2.2
Relative % Range of %K: 8.1
Relative % Range of %Fe: 18.5
SHOW CALCULATIONS – Note show the calcs for just one trial.
Show both %K and %Fe. Do not take up more than two lines worth of space for each.
Observations: when more titrant was added, the solution got darker and started to precipitate
Trial #1: (.2061M)(.00823L)=.00170mol*(39.10g/mol)=(.0665/.296)*100=22.5%K
16.60mL-8.23mL=8.37mL/1000=(.00837L)(.2061M)=(.00172)*(1/3)=5.75E4*(55.85g/mol)=(.03211g/.296)*100=10.84%Fe
Percent by Mass of C2O4
Trial 1
Trial 2
Trial 3 Trial 4
Median Molarity KMnO4 0.0186M 0.0189M 0.0186 0.0192
Mass of Sample
0.150g
.151g
.151g
.145g
Initial Volume
.7mL
.1mL
0.0mL 0.0mL
Final Volume
20.9mL 20.2mL 19.1mL 19.3mL
Total Volume
20.2mL 20.1mL 19.1mL 19.3mL
% C2O4
55.1%
55.4%
52.1%
56.1%
Median %C2O4:55.25
Range:4
Relative % Range:7.2
SHOW CALCULATIONS – Trial 3: (0.01862M)(0.0191L)=(.000356mol
KMnO4)*(5/2)=0.0008891*(88g/mol)=[0.07824g/0.151g]*100=52.1%
Observations: Underwent many color changes before becoming pink after titration. Started green and turned
clear after more titrant was added.
Data Summary
Trial 1
% H2O
5.07
% K+
22.5
% Fe+3
10.8
Trial 2 Trial 3
4.44
5.09
24.4
13.0
Median
5.07
23.5
11.9
Range
0.65
1.9
2.2
Relative % Range
12.82%
8.1%
18.5
% C2O4-2
55.1%
55.4%
56.08% 55.25
4
7.2
Empirical Formula
% of each component
Grams (assuming 100g total)
Molar Mass of each component
% H2O
5.07%
5.07g
18.0g
Moles of each component
.281mol
Unrounded ratio of each component
1.31
Rounded ratio of each component
1.0
Empirical Formula _________K3Fe(C2O4)3*H2O___
Molecular Mass_____455.15g/mol_________
% K+
23.5%
23.5g
39.10
g
.601m
ol
2.82
3.0
% Fe+3
11.9%
11.9g
55.85g
% C2O4-2
55.25%
55.25g
88.0g
.213mo
l
1.0
1.0
.629mol
2.95
3.0
Net Charge
H2O
Oxidation Charge 0
Total Charge ____0_
K+
+3
Fe+3
+3
C2O4-2
-6
Percent Yield
Actual Yield
12.706
Theoretical Yield 17.96
% Yield
70.75
SHOW CALCULATIONS – Show calcs for both theoretical yield and percent yield.
Theo. Yield: (16.0mL)(0.400g/mL)=(6.4g)/(162.2g/mol)=0.03946 mol of
FeCl3*455.15g/mol=17.96 g theoretically
% Yield: [(12.706)/(17.96)]*100=70.75%
DISCUSSION
The percent yield calculated for the experiment was 70.75% and although it is a high
value it shows that errors occurred in the experiment. One section that might have contained
sources of error is the dehydration process. The relative range for percent water is relatively
high, 12.82%, compared to the other components of the iron salt. To lower this range and make
the experiment more accurate, the iron salt should have been placed into the oven for a third
period of time, but due to time constraints this was not an option. Another source of error could
have come from the titration of the iron salt to determine the percent amount of Fe3+ in the
crystalline structure. Like the percent range of water, the range for iron ions is very large at 18.5
%. The large range could have come from two different lab groups titrating the same iron salt.
Due to human error, splashing out of the container, or titrating past the desired point the results
could have yielded such large ranges. The ranges for oxalate and potassium ions are close to one
another showing that these two ions were calculated more accurately in relation to one another.
The calculated percentage range of each of the component of the iron salt adds up to
95.72%. This value is very close to 100% and shows that the amount of calculated components
was correct thus making the empirical formula correct as well. The biggest difference in percent
ranges comes from the iron ion which means that more iron could have been calculated to have
been within the salt. The source of error for this ion occurred during the second titration and
could have been caused by several mistakes such as those listed above. To a smaller extent, the
amount of water in the salt could have also been a source of error. The salt was found to only
contain a small amount of water and perhaps with another heating more water could have been
removed making the results more accurate and the total percent closer to 100%.
For the iron salt the overall charge came out to be equal to zero, solidifying the accuracy
of the results of the experiment and the correctness of the calculated empirical formula. Since the
iron salt is a neutral salt and it’s overall charge should have come out to be equal to zero. In
order to find the charge of the salt, the individual components had to be rounded in order to
determine the ratio in the empirical formula. H2O’s unrounded value was 1.31 and was rounded
down to 1.0 since it was too low, K+’s unrounded was 2.82 so it got rounded up to 3.0 since it
was close, Fe3+ was calculated to be exactly 1.0 and C2O4 was found to be 2.95 so it got rounded
up to 3.0 since it so close. The percentage range for oxalate was small which makes the results
more precise and closer to a whole number when rounding. The percent range for potassium was
also very low so its values were also close to a whole number but not as close as oxalate;
however, the percent range for H2O was higher than potassium and oxalate so its unrounded
values were farther away from a whole number. Based on the results calculated in the
experiment, the charge of the iron salt, the total percent of the salt, and the percent yield of the
experiment the empirical formula found by synthesizing and analyzing the salt was correct.
Some ways to improve the experiment would be to crush up the iron salt more before
dehydrating the crystals to ensure that all water is taken out of the crystalline structure. The
water in the structure seemed to be a source error at some points in the experiment.