Electrochemistry

• In a redox reaction, the substance that undergoes oxidation is called the reducing agent, and the substance that undergoes reduction is called the oxidizing agent.
• Electrochemistry is the study of production of electricity from energy released during spontaneous chemical reactions and the use of electrical energy to bring about non-spontaneous chemical transformations.
• The subject of electrochemistry is of importance both for theoretical and practical considerations.
• A large number of metals, sodium hydroxide, chlorine, fluorine and many other chemicals are produced by electrochemical methods.
• Batteries and fuel cells convert chemical energy into electrical energy and are used on a large scale in various instruments and devices.
• The reactions carried out electrochemically can be energy efficient and less polluting.
• Electrochemistry is important for creating new technologies that are ecofriendly.
• The transmission of sensory signals through cells to brain and vice versa and communication between the cells are known to have electrochemical origin.
• Electrochemistry is a very vast and interdisciplinary subject.
• After studying this Unit, you will be able to describe an electrochemical cell and differentiate between galvanic and electrolytic cells.
• You will be able to apply Nernst equation for calculating the emf of galvanic cell and define standard potential of the cell.
• Molar conductivity =  = –3 –1 248 × 10 S m 20 mol m = 124 × 10 –4 S m 2 mol –1.
• The cell constant is given by the equation: Cell constant = G* = conductivity × resistance = 1.29 S/m × 100 W = 129 m –1 = 1.29 cm –1.
• The conductivity of a solution at any given concentration is the conductance of one unit volume of solution kept between two electrodes with area of cross section A and distance of unit length.
• Molar conductivity of a solution at a given concentration is the conductance of the volume V of solution containing one mole of electrolyte kept between two electrodes with area of cross section A and distance of unit length.
• The electrical resistance of a column of 0.05 mol L –1 NaOH solution of diameter 1 cm and length 50 cm is 5.55 × 10 3 ohm.
• Conductivity of 0.02 mol L –1 KCl solution = cell constant / resistance = G R = –1 129 m 520  = 0.248 S m –1.
• Molar conductivity increases with decrease in concentration.
• Alternatively, k = –1 1.29 cm 520  = 0.248 × 10 –2 S cm –1.
• You will be able to derive relation between standard potential of the cell, Gibbs energy of cell reaction and its equilibrium constant.
• Predict the products of electrolysis in an aqueous solution of AgNO3 with silver electrodes.
• Predict the products of electrolysis in a dilute solution of H2SO4 with platinum electrodes.
• Using the standard electrode potentials given in Table 3.1, predict if the reaction between Fe3+ (aq) and Br– (aq) is feasible.
• Predict the products of electrolysis in an aqueous solution of AgNO3 with platinum electrodes.
• Using the standard electrode potentials given in Table 3.1, predict if the reaction between Br2 (aq) and Fe2+ (aq) is feasible.
• Predict the products of electrolysis in an aqueous solution of CuCl2 with platinum electrodes.
• Using the standard electrode potentials given in Table 3.1, predict if the reaction between Fe3+ (aq) and I– (aq) is feasible.
• Using the standard electrode potentials given in Table 3.1, predict if the reaction between Ag+ (aq) and Cu(s) is feasible.
• The current flow for the electrolysis of copper and zinc was 2.17 amps.
• Using the standard electrode potentials given in Table 3.1, predict if the reaction between Ag(s) and Fe3+ (aq) is feasible.
• You will be able to define resistivity (r), conductivity (k) and molar conductivity (✆ m) of ionic solutions.
• You will be able to differentiate between ionic (electrolytic) and electronic conductivity.
• The values of standard electrode potentials for some selected half-cell reduction reactions are given in Table 2.1.
• If the standard electrode potential of an electrode is greater than zero then its reduced form is more stable compared to hydrogen gas.
• Lithium has the lowest electrode potential indicating that lithium ion is the weakest oxidising agent while lithium metal is the most powerful reducing agent in an aqueous solution.
• As we go from top to bottom in Table 2.1 the standard electrode potential decreases and with this, decreases the oxidising power of the species on the left and increases the reducing power of the species on the right hand side of the reaction.
• Electrochemical cells are extensively used for determining the pH of solutions, solubility product, equilibrium constant and other thermodynamic properties and for potentiometric titrations.
• The electrode reaction for the cell is the sum of the two reactions: Zn(s) + Cu 2+ (aq) Æ Zn 2+ (aq) + Cu(s) with an emf of the cell equal to E o cell = E o R – E o L = 0.34V – (– 0.76)V = 1.10 V.
• Metals like platinum or gold are used as inert electrodes in electrochemical cells, providing their surface for oxidation or reduction reactions and for the conduction of electrons.
• If the standard electrode potential is negative then hydrogen gas is more stable than the reduced form of the species.