Standardization of Ammonium Ferrous Sulfate Solution

Significance of the Topic

Thermometric titration of hexavalent chromium relies on a precisely standardized ferrous titrant to ensure accurate redox measurements. Establishing the exact concentration of ammonium ferrous sulfate solution is critical for reproducible results in environmental monitoring, quality control and trace analysis of chromium species.

Objectives and Study Overview

This application note describes the standardization protocol for 0.1 mol per liter ammonium ferrous sulfate using a 0.01 mol per liter potassium dichromate primary standard. The aim is to verify titrant strength and ensure compatibility with thermometric titration of CrVI solutions.

Methodology and Instrumentation

The protocol employs a thermometric titrator equipped with a Dosino dosing unit and 802 magnetic stirrer. Key parameters include a titrant delivery rate of 2 mL per minute, a single exothermic endpoint detection, a data smoothing factor of 40, stirring speed at level 6 and a 10 second delay before measurement begins. Pre-dosing routines deliver aliquots of dichromate solution in decreasing volumes alongside fixed sulfuric acid additions. Deionized water complements the sample matrix to a 30 mL total volume prior to titration.

Main Results and Discussion

Standards of potassium dichromate were titrated in volumes ranging from 1.5 to 9 mL. The resulting millimoles of dichromate and corresponding ferrous titration volumes were plotted. Linear regression yielded a slope of 62.3809 and an R2 of 0.999996. From the slope, the ferrous concentration was calculated as 0.09618 mol per liter, slightly below the nominal 0.1 mol per liter target.

Benefits and Practical Applications

Accurate standardization of the ferrous titrant enhances the reliability of thermometric titration for chromium analysis in laboratories. This method reduces uncertainty in endpoint detection and supports compliance with regulatory requirements in water, soil and industrial effluent testing.

Future Trends and Applications

Advancements in sensor sensitivity, automated dosing algorithms and integration with digital data systems will further improve thermometric titration workflows. Potential applications include rapid on-site monitoring of metal contaminants and high-throughput screening in process control environments.

Conclusion

This note demonstrates a robust procedure for verifying the concentration of ammonium ferrous sulfate titrant. The high linearity and reproducibility of the method ensure confidence in subsequent thermometric titrations of chromium VI solutions.

Reference

Thermo Scientific Thermometric Titration Application Note No H-032 Standardization of Ammonium Ferrous Sulfate Solution