Vincent Kurp
Quantitative Analysis
Lab 2: Gravimetric Analysis of Iron as Fe2 O22
Purpose:
The purpose of this experiment was to determine the amount of Iron present in a sample
containing an unknown amount of Iron. To do this we dissolved the sample in acid and filtered out the
precipitate in order to isolate our product. We then formed a solid product of iron oxide by the method
of dehydration.
Fe3+ + 3 H2O → FeOOH * H2O (s) + 3 H+
2 FeOOH * H2O → Fe2O3 (s) + 2 H2O
Procedure:
Three crucibles were heated to redness for 15 minutes over a Bunsen burner then weighed after
being allowed to cool to room temperature. We then calculated the amount of unknown needed to
produce approximately 0.03 g of Iron and weighed out three samples of this amount. 10 mL of HCl were
added to each sample in a 500 mL beaker to dissolve the Iron, and then the samples were filtered to
remove any insoluables. To each solution 5 mL of 6 M nitric acid was added and were boiled for two
minutes then diluted to 200 mL. Then 3M ammonia was added until the solutions tested basic. The
solutions were boiled for five minutes and the supernatant was decanted through ashless filter paper
and washed with warm 1% ammonia nitrate. The precipitate captured was our final product, Fe2 O22 . A 1
mL aliquot of filtrate was acidified using 0.1M nitric acid, and then ten drops of Silver Nitrate were
added. If the solution appeared cloudy, the precipitated Fe2 O22 was washed with more warm 1%
ammonia nitrate and this was repeated until the filtrate tested non-cloudy. The filter papers were
transferred into their designated crucibles and dried for at least 24 hours. The dried samples were
heated in the crucibles using a Bunsen burner and the filter paper was ignited and burned until
disintegrated and no paper residue was left. The crucibles were then allowed to cool before being
weighed repeatedly until consistent measurements were obtained.
Data:
Crucible weight measured in grams (g)
Crucible 1
Crucible 2
Crucible 3
Trial 1
19.0303
19.8251
23.8583
Trial 2
19.0269
19.8228
23.8568
Average
19.0286
19.82395
23.85755
Unknown weights measured in grams (g)
Unknown 1
Unknown 2
Unknown 3
0.1997
0.1974
0.1979
Final Masses of Crucibles with Product in grams (g)
Trial 1
19.0447
19.8386
23.8698
Crucible 1
Crucible 2
Crucible 3
Trial 2
19.0443
19.8390
23.8700
Average
19.0445
19.8388
23.8699
Mass of Product in grams (g)
Crucible 1
Crucible 2
Crucible 3
0.01590
0.01485
0.01235
Iron Content of Fe2O3 sample in grams (g)
Crucible 1
Crucible 2
Crucible 3
0.01112
0.01039
0.008639
Crucible 1
Crucible 2
Crucible 3
69.93%
69.97%
69.95%
Percent Yeild
Calculations:
Average Mass = (mass 1+ mass 2)/2
Ex: (for Crucible 1 mass)
(19.0303+19.0269)= 19.0286
Mass of Ferrous ammonium sulfate needed to produce 0.03g of Fe2O3
𝑔
392.14
𝐹𝑒 1 𝑚𝑜𝑙 𝐹𝑒𝑁𝐻4 (𝑆𝑂4 )2
1 𝑚𝑜𝑙 𝐹𝑒2 𝑂3
2 𝑚𝑜𝑙 𝐹𝑒
1
𝑚𝑜𝑙
0.03𝑔 𝐹𝑒2 𝑂3 ×
×
×
×
×
= 0.196 𝑔
159.6933 𝑔 1 𝑚𝑜𝑙 𝐹𝑒2 𝑂3
1 𝑚𝑜𝑙
1 𝑚𝑜𝑙 𝐹𝑒
0.75
Iron content of Fe2O3 sample
𝑔𝑟𝑎𝑚𝑠 𝑜𝑓 𝐹𝑒2 𝑂3 ×
1 𝑚𝑜𝑙 𝐹𝑒2 𝑂3
2 𝑚𝑜𝑙 𝐹𝑒
55.85 𝑔 𝐹𝑒
×
×
= 𝑔𝑟𝑎𝑚𝑠 𝑜𝑓 𝐹𝑒
159.69 𝑔
1 𝑚𝑜𝑙 𝐹𝑒2 𝑂3
1 𝑚𝑜𝑙 𝐹𝑒
Ex: (for crucible 1)
0.01590 𝑔 ×
1 𝑚𝑜𝑙 𝐹𝑒2 𝑂3
2 𝑚𝑜𝑙 𝐹𝑒
55.85 𝑔 𝐹𝑒
×
×
= 0.01112 𝑔
159.69 𝑔
1 𝑚𝑜𝑙 𝐹𝑒2 𝑂3
1 𝑚𝑜𝑙 𝐹𝑒
Percent Yield
𝑃𝑒𝑟𝑐𝑒𝑛𝑡 𝑌𝑖𝑒𝑙𝑑 =
Ex: (for Crucible 1)
𝐴𝑐𝑡𝑢𝑎𝑙 𝑌𝑖𝑒𝑙𝑑
× 100
𝑇ℎ𝑒𝑜𝑟𝑒𝑡𝑖𝑐𝑎𝑙 𝑌𝑒𝑖𝑙𝑑
0.01112 𝑔
× 100% = 69.93%
0.01590 𝑔
Discussion:
The function of the nitric acid in step 2 of the experiment was to oxidize the iron that was
present in our samples. Our results for this experiment were precise but not as accurate as we had
hopes. We were only able to recover around 70% of the iron that we believed was present, but our
results were consistent which is good.
Conclusion:
Sources of error could have occurred during the measuring of the masses of the crucibles. If the
crucibles weren’t completely cooled after heating it could have affected our measurement. I believe the
most significant source of error took place during the process of filtering the product through the
ashless filter. Due to the miniscule amount of product, any amount of it that was lost no matter how
small had a very significant effect. Any residue that was left in the beaker after decanting, or any
product that got through the Buchner funnel had a significant effect on our final measurement.
Qualitative analysis is a method of chemical analysis to calculate the amount of initial analyte by
examining the change from the initial mass of a sample and the final mass of the product that is isolated.
For this experiment I would suggest to use new crucibles so there wouldn’t be any residue from any past
experiments. I would also suggest using a more efficient way to filter out our product rather than using a
Buchner funnel to avoid any possibilities of losing product through the filter paper or leaving any behind
when transferring the product to the crucible.