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).
Dehydration/Ignition
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.