Resumen de Quantitative Cathodic Preparation of Selected Aqueous Reagents Used in an Undergraduate Laboratory
Samuel Melaku, Rajeev B. Dabke
A guide for instructors and laboratory assistants to prepare several aqueous reagents used in an undergraduate laboratory is presented. Dilute reagents consisting of OH–(aq), Fe2+(aq), and Sn2+(aq) were prepared by electrolytic reduction of the respective precursors at the cathode. Concurrently, water was electrolyzed at the anode. A known mass of anhydrous Na2CO3 (a primary standard) was added to the anode compartment. Electrolytically produced H+(aq) ions were titrated in situ against Na2CO3 using bromophenol blue indicator. The electrolysis was promptly stopped when the indicator changed color from blue to yellow. The amount of H+(aq) produced at the anode was determined from the mass of Na2CO3. Because the same current passed through the electrolysis cell, the stoichiometric relation between the cathode and anode reactions facilitated the determination of the reagent prepared at the cathode. The concentration of reagent prepared at the cathode was independently confirmed by the volumetric titration method. The electrolysis cell, powered by 18 V dc power supply, eliminated the requirement of a coulometer or a constant current power source. Setup of an electrolysis cell and experimental details for preparing reagents are presented.
