Question

Consider the titration of 25.0 mL of 0.0500 M Sn2+ with 0.100 M Fe3+ in 1 M HCl to give Fe2+ and Sn4+, using a Pt and calomel electrodes. (a) write a balanced titration reaction (b) write two half-reactions fo the indicator electrode (c) write two Nerst equations for the cell voltage (d) calculate E at the following volumes of Fe3+: 1.0, 12.5, 24.0, 25.0, 26.0, and 30.0 mL. Sketch the titration curve.

Answer 1

1. The overall balance titration equation is:

1. Half Reactions:

^Anode:

              Sn²⁺              Sn⁴⁺ + 2e^- … E₀ = 0.139

^Cathode:

1. Nernst Equation:

It is the relation between the reduction potential of an electrochemical reaction (either half-cell or full cell) to the standard electrode potential, temperature and and activities of the electroactive species (often represented by concentrations).

It is represented as

Where

·         E is the half-cell potential at the temperature of interest

·         E₀ is the standard half-cell potential

·         R is the universal gas constant: R = 8.314472(15) J K⁻¹ mol⁻¹

·         T is the temperature in kelvins

·         F is the Faraday constant, the number of coulombs per mole of electrons: F = 9.64853399(24)×10⁴ C mol⁻¹

·         n is the number of moles of electrons transferred in the cell reaction or half-reaction

·         Q is the reaction quotient.

The Nerst equation is generally expressed in base-10 log form. For 25 C:

Thus

Nernst equation for the cathode:

Nernst equation for the anode: