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Kenneth Kang

Tuesday, December 03, 1996

Chemistry

Iron, Copper, and Sulfate Stoichiometry

To find the percent yield and to apply out stoichiometry calculations, we observed an Iron(II), Copper(II) Sulfate replacement reaction.

Purpose

The experiment demonstrates the theoretic calculations and the real world percent yield. It also relies on the ability to perform stoichiometric calculations and measurements.

Prelab Briefing

Dissolving copper(II) sulfate in a 1g (12.5g) to 4 mL (50mL) water solution under gentle heat, add the iron filings (2.24g) and let rest for 10 minutes. Setup a filter and funnel over an Erlenmeyer flask. Pour cooled solution into the filtration device and wash down all the sediment. Let the filter paper dry for a day and measure the mass of the copper which should remain.

Procedure for Impatient People

  1. 12.5g CuSo4
  2. 50 mL water, combine, stir, heat, do not boil
  3. 2.24 g Fe2+, add
  4. Setup flask, filter and funnel
  5. Pour cooled solution and sediment
  6. Let filter dry
  7. Measure mass of sediment on filter

Observed Reaction

The reactions was uneventful. The solution exhibited no color change in the prescribed ratio, but it did turn from blue to yellow when the ratio of copper sulfate and iron was changed to 1:1.

Results


CuSO4                         2.0 g        1.253x10-2 mol       

Fe                            2.0 g        3.581x10-2 mol       

Cu (predicted)                0.796 g      1.253x10-2 mol       

Fe (theoretic residue)        1.30 g       2.328x10-2 mol       

Cu + Fe (theory)              2.096 g                           

Cu + Fe (observed)            2.2 g                             

Percent Yield                 105%                              



Table 1: First Experiment Calculations


CuSO4               5.300 g      3.321x10-2 mol       

Fe                  0.950 g      1.701x10-2 mol       

Cu (predicted)      1.081 g      1.701x10-2 mol       

Cu (observed)       1.375 g                           

Percent Yield       127%                              



Table 2: Second Experiment Calculations

The limiting reagent is set in bold. The first calculation must take into account the excess iron, because iron will get weighed along with the copper. The second experiment has the limiting reagents reversed, but the excess copper sulfate drains down with the rest of the solution.

Analysis

Due to a procedural oversight, the filter paper was not measured to the highest accuracy possible. The mass, recorded by other groups, used for this experiment was 1.0 g. Other groups recorded different masses for the filter paper which suggests that either the filter papers are not uniform, the scales are messed up, or the weighing procedure had errors.

In addition to the uncertainty of the filter paper masses, the filter paper, after drying for twenty-four hours, showed signs of the blue CuSO4 which creates more error in our experiment. Quantification of this error margin can be done by soaking the paper in distilled water so that the CuSO4 can dissolve, leaving the iron and copper.

Furthermore, there is the possibility that not all the iron reacted with the copper sulfate. Because there was no method to check, we assumed that all the iron was iron(II). When the experiment is recalculated with iron(III), trial #2 has an 84% yield with a theoretic mass of 1.621 g, and trial #1 has a 94% yield with a theoretic combined mass of 2.329 g. This is a possible answer, but the error enumerated above make it difficult to make a firm determination on the composition of the iron.

Conclusion

The experiment trial had an error margin of 27% at the greatest 5% at the lowest and an average of 13.5% error. Because of the lack of precise data on the filters we used, we were unable to gain more insight into the problem with iron(II) and iron (III). The presence of residue on the filter also disturbed the readings. It would be nice to be able to add the extra step where the filter is put in water to dissolve away the CuSO4 and FeSO4. This additional procedure might allow investigation into the "natural" occurrence ratios of iron(II) and iron(III). This experiment seems to have no immediate applications to the real world.