Analysis of Iron Tablets by Titration with Potassium Manganate(VII)

Introduction

Iron is an essential mineral required for the production of hemoglobin, myoglobin, and several enzymes. Iron deficiency is one of the most common nutritional deficiencies worldwide, leading to anemia and other health issues. Iron supplements are widely available in the form of tablets containing ferrous sulfate (FeSO7HO) or ferrous fumarate.

This experiment describes the quantitative analysis of iron tablets by redox titration using potassium manganate(VII) (KMnO) as the titrant. The method is based on the oxidation-reduction reaction between Fe ions in the dissolved iron tablet and the purple permanganate ions.

Principle of the Analysis

The analysis is based on the redox reaction between iron(II) ions and permanganate ions in acidic medium. In this reaction, iron(II) is oxidized to iron(III), while permanganate(VII) is reduced to manganese(II) ions:

The purple color of permanganate(VII) serves as its own indicator. As the titration proceeds, the purple color is decolorized by the reaction with iron(II) ions. When all the iron(II) has been oxidized, any additional permanganate gives a permanent pink color to the solution, marking the endpoint of the titration.

From the stoichiometry of the reaction, one mole of permanganate reacts with five moles of iron(II). This relationship allows us to calculate the amount of iron in the tablet.

Materials and Equipment

Chemicals	Equipment
Iron tablets (containing ferrous sulfate)	Burette (50 mL)
Potassium manganate(VII) solution (0.02 M)	Pipette (25 mL)
Dilute sulfuric acid (2 M)	Volumetric flask (100 mL)
Distilled water	Conical flask (250 mL)
	Beakers, measuring cylinders
	Filter funnel and filter paper
	Balance
	Magnetic stirrer (optional)

Preparation of Solutions

Standardization of Potassium Manganate(VII)

Potassium manganate(VII) solutions are not primary standards because they slowly decompose in solution, especially in the presence of light. They must be standardized before use. However, for this experiment, we will assume the potassium manganate(VII) solution has already been standardized and has a known concentration of approximately 0.02 M.

Preparation of Iron Tablet Solution

Titration Procedure

Calculations

To determine the amount of iron in the tablets:

Step 1: Calculate the average volume of potassium manganate(VII) used from your concordant titres.

Step 2: Calculate the moles of permanganate used:

Step 3: Calculate the moles of iron(II) in the titrated sample:

Step 4: Calculate the moles of iron(II) in the original solution:

Step 5: Calculate the mass of iron in all tablets:

Step 6: Calculate the mass of iron per tablet:

Step 7: Calculate the percentage of iron in the tablets:

Sample Calculation

Suppose 5 tablets with a total mass of 2.00 g were dissolved and made up to 250 mL. 25.00 mL of this solution required an average of 12.40 mL of 0.0200 M potassium manganate(VII) solution.

Moles of KMnO in 12.40 mL:

Moles of Fe in 25.00 mL:

Total moles of Fe in 250 mL:

Total mass of Fe in 5 tablets:

Mass of Fe per tablet:

Percentage of Fe in tablets:

Sources of Error

• Oxidation of iron(II) by air: Iron(II) can be oxidized to iron(III) by atmospheric oxygen, especially in neutral or alkaline conditions. This can be minimized by working in acidic medium and completing the analysis promptly.
• Impurities in iron tablets: Some excipients in the tablets may interfere with the titration or be oxidized by permanganate.
• Decomposition of potassium manganate(VII): KMnO solutions decompose over time, especially when exposed to light. Solutions should be freshly prepared or periodically standardized.
• Endpoint determination: The purple color of permanganate makes the endpoint distinct, but some individuals may detect it at different intensities, leading to variation in titres.
• Titration technique: Errors in reading the burette, adding titrant too quickly near the endpoint, or not swirling adequately can affect results.

Safety Considerations

Applications

This quantitative analytical technique has several important applications:

• Quality control: Pharmaceutical companies use similar methods to verify the iron content in iron supplements.
• Clinical analysis: Blood iron levels can be determined using similar redox titrations.
• Environmental monitoring: Iron content in water and soil samples can be analyzed using permanganate titration.
• Industrial processes: The method can be adapted to analyze iron in various industrial products and raw materials.

Conclusion

The redox titration of iron tablets with potassium manganate(VII) is a classic analytical technique that provides accurate quantitative results. This method demonstrates the practical application of redox chemistry in analytical procedures and remains relevant in various fields including pharmaceutical analysis, clinical diagnostics, and environmental monitoring.

The self-indicating nature of permanganate titrations, combined with the well-defined stoichiometry of the reaction between permanganate and iron(II), makes this a reliable technique for determining iron content with good precision and accuracy.