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1. Gravimetric Determination of Iron as Fe2O3 Experiment 3
2. Purpose To determine the amount of Iron (III) in a sample of unknown using the gravimetric analysis method.
3. Gravimetric Analysis? Any analytical method that relies on measuring the mass of a substance to complete the analysis.
4. How to obtain the product? Precipitation
Treating the analyte with a suitable counter ion (base).
Heated to dryness
To achieve a reproducible, stable composition.
To change the chemical form of the precipitant.
5. Precipitation Measures taken to reduce super saturation and form easily filtered particles (precipitate):
High temperature during precipitation.
Slowly adding and vigorously mixing the reagents.
Maintaining a large sample volume.
Using homogenous precipitation.
6. Reaction! Formation of precipitate:
Fe3+ + (2 + x)H2O (base)? FeOOH.xH2O(s) + 3H+
FeOOH.xH2O(s) (heat)? Fe2O3(s)
7. Question? Why is the analyte treated with a counter ion?
8. Answer To promote precipitation.