Gravimetric Determination of Iron as Fe2O3
Laboratory Experiment 2
February 19, 2013
In the Gravimetric determination is the measurement of mass in two different forms precipitation and volatilization. In our experiment we will be using the precipitation form which isolates an ion in a solution by a precipitation reaction, filtering, purifying by wash method, conversion to product of known composition, and final weigh of the product comparing the mass difference of theorictal and actual. This method identified the weight percent of iron in an unknown sample. Three samples are taken to limit percent error. In the results of the three samples 1 had a percent of 10.764 Fe (III), sample 2 had a percent of 11.725 Fe (III), and sample 3 with a percent of 12.216 Fe (III). The average sample percent was 11.568 compared to given amount percent of 12.90. In theory with a loss of 1.332 this experiment was overall successful.
In this lab the purpose was to use the gravimetric determination procedure to identify the weight percent of iron in an unknown sample. Three samples were collected and analyzed. Iron can be analyzed by precipitating the hydrated iron oxide from a basic solution. After the basic solution is hydrated the process is then followed by complete dehydration to give solid iron oxide.
Methods and Materials:
Needed in the experiment was;
* Crucibles, Metal rings, Wire triangles, Burners, Funnels, Filter Paper, Beakers, Glass rod, Diluted ammonium hydroxide solution, Nitric acid solution, Silver nitrate solution, NH4NO3 solution, Distilled water. Below are some methods used in experiment.
This experiment was a multiple session lab.
Obtain three crucibles and desiccator. Bring the three porcelain crucibles and caps to constant mass by heating to redness for 15 minutes over a burner, use fig. 1 for method reference. Place the heated crucibles in the desiccator to cool for approximately 30 minutes and weigh. This was left overnight and completed the second trial in the next session with successive weighing agreed within 0.30mg. (Keep constant numbering with crucibles throughout experiment) We measured out 1.5g of three samples of the unknown that was given to us. Each sample was dissolved in 10 mL of 3M HCl (with heating necessary). 5mL of 6 M HNO3 was obtained to filtrate, and boil for a few minutes to ensure that all iron is oxidized to Fe (III). The samples was diluted to 200mL with distilled water and add 3 M ammonia with constant stirring until the solution was basic (as determined with pH indicator paper). After solution becomes basic, digest the precipitate by boiling for 5 minutes and allow the precipitate to settle. We then decanted the supernatant liquid through coarse, ash less filter paper (Whatman 41 or Schleicher and Schuell Black Ribbon, as in fig. 2 -18 and 2 -19 in textbook.). Keep liquid lower than 1 cm from the top of the funnel. Our precipitate was first washed repeatedly with hot ammonium hydroxide solution, by miscommunication. Then washed with the corrected heated ammonium nitrate and left it to drain overnight until next session. We continued to wash supernatant until little or no Cl- is detected in filtered supernatant. Detect the Cl- by acidifying a few milliliters of filtrate with 1 mL of dilute HNO3 and adding a few drops of 0.1 M AgNO3. If precipitate is observed, Cl- is present. After identifying that there was not any Cl- present we allowed the filter to drain overnight covered with ventilation. Carefully, the paper was lifted out of the funnel, folded (fig.2), and transferred all dried substance to crucible and any substance that is not completely dry place into beaker and into the heater for half an hour. Those placed in beaker was then placed into the crucibles that were brought to constant mass. With the paper and substance in the crucible it was placed over a...