Monique Gray
Experiment 2
Quantitative Analysis
Experiment 2: Gravimetric Determination Of Iron Fe 2O3
Introduction
The purpose of this experiment is to understand and facilitate gravimetric analysis of a source. Thus, in this
experiment, one will analyze the amount of a iron in an unknown sample by precipitating, from basic solution, the
hydrated iron oxide. The reaction is immediately followed by a dehydrated reaction to produce the solid Fe 2O3.
Procedure
- Fire three porcelain crucibles with caps to a reproducible weight by heating in a 900°C furnace for ten minutes
and taking the mass after cooling for fifteen minutes.
- Repeat this procedure about three times or until the masses of each crucible is within 0.0005 units of each other.
- Accurately weight enough 3 samples of an unknown to produce ~0.03g. Assume that your sample is 75% ferrous
ammonium sulfate. Dissolve each sample in 3mL HCl (heat if necessary and filter impurities if applicable.)
- Add 5mL 6M HNO3 and bring to a steady boil for about two minutes.
- Dilute sample to 200mL with distilled water. (In the same container one is currently using.)
- Add 3mL Ammonia until solution us basic. (Use pH paper for this step.)
- Dissolve precipitant by boiling solution for about five minutes.
- Decant/filtrate the supernate thru the ashless filter paper and the wash with 1% NH 4NO3 (acidify with dilute nitric
acid and sliver nitrate.) (Repeat the washing step until no Cl- ion is present in solution. Thus, solution should appear
clear.)
- Cover with watch glasses and allow filter paper to dry for about 24 hrs.
- Ignite the filter paper and immediately cover with crucible cap. (Repeat for all three crucibles.)
- Upon cooling, weight the crucibles again and repeat the drying process until the masses are consistent with each
other.
Data
Crucible 1
Crucible 2
Crucible 3
Mass of Crucibles Before Adding Iron Samples
46.3599g
46.3567g
46.3563g
43.3560g
43.3540
43.3546g
47.7605g
47.7599g
47.7596g
Avg: 46.3576g
Avg: 43.3548g
Avg: 47.7600g
Monique Gray
Experiment 2
Crucible 1
Crucible 2
Crucible 3
Mass of Crucibles after Adding Iron Samples
46.3867g
46.3868g
-----------------43.3820g
43.3816g
-----------------47.7866g
47.7865g
----------------------
Mass of Iron Samples before Experiment
1: 0.1961g
2: 0.1959g
3: 0.1962g
Calculating the Average Mass of a The Crucibles
Mass 1+Mass 2+Mass 3
3
= average mass
46.3599g+46.3599g+46.3563g
3
= 46.3576g
Amount of Sample to Produce 0.03g of Fe 2O3
0.03 g Fe2 O3 ×
1 mol Fe2 O3 2 mol FeOOH 1 mol FeSO4 (NO4 )2 SO4 392.12 g
1
×
×
×
×
= 0.196 g
159.6933 g
1 mol Fe2 O3
1 mol FeOOH
1 mol
0.75
*To obtain mass of product subtract the masses of the crucibles before and after sample was added, just the
averages:
Example: 46.38675 – 46.3576g = 0.02915g (mass of product for crucible 1)
Percent of Iron in Sample =
grams of Fe as product
×
grams of the reactant
100%
Example: 0.02915g/0.1961g x 100 = 14.86%
Theoretical Yield of Fe2O3
%Fe3+ in sample =
Grams of Fe2 O3
1 mol Fe2 O3
2 mol Fe3+
55.85 g Fe3+
×
×
×
= Grams of Fe3+
1
159.69 g Fe2 O3 1 mol Fe2 O3
1 mol Fe3+
%Fe3+ in sample =
0.02915g
1 mol Fe2 O3
2 mol Fe3+
55.85 g Fe3+
×
×
×
= 0.02029gFe3+
1
159.69 g Fe2 O3 1 mol Fe2 O3
1 mol Fe3+
actual yield
Percent yield of Fe3+ = theoretical yield × 100%
Example 0.02029g / 0.02915g x 100 = 69.6054% yield of Fe3+
Monique Gray
Experiment 2
Conclusion
Using gravimetric analysis we were able to determine the mass of the synthesized Fe2O3.
I think the single most important source of error in this experiment would have to be the handling of the crucibles
and handles of the ashless filter paper when the iron sample was on it. Yes, my results do justify my answer. This
was because at the moment we didn’t know a proper technique for handling crucibles, so the handling of them
could have made a results differ. Also, another error could have been to the fact that we ran out of ashless filter
paper that was the same size of the funnel used for vacuum filtration so this may have made have contributed to a
low yield.
The purpose of using nitric acid was to ensure the all iron was converted into the Fe (III) cation.
Gravimetric analysis is a method that uses the total mass collected at the end of the experiment to accurately and
precisely determine the mass of a product sample (analyte).
I would use a better technique to handle crucibles. I would have probably used tried being a little more careful
when weighting and/or repeating the weighting process of the crucibles before and after the experiment.