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Assay of Ferrous Sulphate by Cerimetry

1. Aim

To estimate ferrous ion in the assigned ferrous sulphate preparation by cerium(IV) oxidation. The exact hydrate, sample basis, and monograph are to be recorded from the assigned current monograph or approved college method in the student record.

2. Requirements

Assigned ferrous sulphate sample, standardized cerium(IV) titrant, prescribed acidic medium and redox indicator or instrumental endpoint, suitable water, burette, pipette, flask, balance, and oxidizer waste container. Follow your college lab manual and instructor's method sheet for titrant concentration, acid identity and strength, sample mass, and endpoint.

3. Theory

Cerium(IV) oxidizes Fe2+ to Fe3+ while it is reduced to Ce3+. The stoichiometric relation is one mole Ce4+ per mole Fe2+. Acidic conditions stabilize the titration chemistry and the approved method defines the endpoint. Air oxidation of the sample before titration biases the result low. The word ferrous sulphate may describe different hydrate forms, so a mass percentage must use the verified formula and monograph basis. [2]

4. Procedure

1. Verify the product monograph, hydrate state, titrant standardization record, acid medium, and endpoint; unresolved details are to be recorded from the assigned current monograph or approved college method in the student record.
2. Weigh or transfer the assigned sample quantity and dissolve promptly using the specified medium.
3. Transfer the verified aliquot to the titration flask and add the prescribed acidic medium and indicator if used.
4. Fill and read the burette with standardized cerium(IV) solution.
5. Titrate to the validated persistent endpoint and record the initial and final burette readings.
6. Repeat as instructed and use the corrected titre, if a blank is specified, to calculate ferrous ion in the aliquot.

5. Calculation, graph, or images as appropriate

Assumed values for calculation practice only: assume the cerium(IV) titre is assumed 10.00 mL and its standardized concentration is assumed 0.1000 mol/L. Neither is a measured result or a preparation instruction.

1. Assumed Ce4+ amount = assumed 0.01000 L × assumed 0.1000 mol/L = 0.001000 mol.
2. From the 1:1 electron-transfer relation, illustrative Fe2+ amount = 0.001000 mol.
3. Using atomic mass 55.85 g/mol, illustrative elemental iron mass = 0.001000 mol × 55.85 g/mol = 0.05585 g, or 55.85 mg in the assumed aliquot.
4. Record ferrous sulphate mass or assay percentage here only after the hydrate, sample mass, dilution factor, and actual titre are known.

6. Result

Report the actual assay only after checking the validated procedure, observed readings, sample basis, and dilution. Record the supervised outcome here. This page is a supervised-activity guide; it does not report a completed case. The calculation deliberately reports elemental Fe2+ in the aliquot so it cannot silently assume an anhydrous or hydrated formula. Safety note: Cerium(IV) titrant is an oxidizer and the acidic medium is corrosive. Work only under teaching-lab supervision with eye and skin protection; collect the titration waste as directed.

7. References

1. Pharmacy Council of India, Pharm.D. Regulations, 2008.
2. East Point College of Pharmacy, Pharmaceutical Inorganic Chemistry Manual.

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