Foundation Year Program Electrochemistry Lecture B Cell potential

Foundation Year Program Electrochemistry Lecture B: Cell potential & applications of electrochemistry 2015 -16

Foundation Year Program Learning outcomes 1. Cell Potential 2. Standard Reduction Potential 3. Standard Cell Potential 4. Applications of electrochemistry 2015 -16

Foundation Year Program Cell potential • A galvanic cell has an ability to push electrons through external circuit. The magnitude of this ability is expressed as a potential in voltage (V). • The maximum potential that a given cell can generate is called its cell potential, Ecell. 2015 -16

Foundation Year Program Cell potential • The value of cell potential depends on the property of electrode metal and its ability to gain electron under standard conditions. ü Standard conditions used for the electrochemical measurements: c = 1 M; p = 1. 0 atm; T = 298 K ü The potential of a cell depends on the concentration of reactants & products 2015 -16

Foundation Year Program Standard reduction potential ü The magnitude of a metal ion’s ability to gain electrons under standard conditions is called standard reduction potential. • Bigger the value – higher the ability to gain electrons • Smaller the value – lower the ability to gain electrons • Written in direction: Mn+(aq) + ne- → M(s) 2015 -16

Foundation Year Program Standard reduction potential 2015 -16

Foundation Year Program Standard reduction potential ü The standard reduction potential of isolated half-cell can’t be measured, but values are assigned by choosing the standard hydrogen electrode as a reference electrode. This is an arbitrary standard set at 0. 00 V 2015 -16

Foundation Year Program Standard hydrogen electrode • Standard hydrogen electrode (SHE) is the arbitrarily assigned half-reaction which is used as the reference value for obtaining other standard electrode potentials. anode: H 2(g) → 2 H+(aq) + 2ē cathode: 2 H+(aq) + 2ē → H 2(g) • Direction depends on the other half cell • An arbitrary potential 0. 00 V is assigned to these half reactions. 2015 -16

Foundation Year Program Standard hydrogen electrode • SHE consists of a platinum electrode dipped into a 1. 00 M acid solution surrounded by hydrogen gas at 1 atm pressure and 25 o. C. • Platinum metal is inert and does not participate in the redox reaction. 2015 -16

Foundation Year Program Standard hydrogen electrode • At anode (-ve): Zn(s) → Zn 2+(aq) + 2ē • At cathode (+ve): 2 H+(aq) + 2ē → H 2(g) • Net reaction: Zn(s) + 2 H+(aq) → Zn 2+(aq) + H 2(g) 2015 -16

Foundation Year Program Increasing E° 2015 -16

Foundation Year Program Standard reduction potential • When two half-cells are connected to make a Galvanic cell, the one with the larger standard reduction potential (greater tendency to undergo reduction) gains electrons from the half-cell with the lower standard reduction potential, which is therefore forced to undergo oxidation. 2015 -16

Foundation Year Program Standard reduction potential Zn(s) → Zn 2+(aq) + 2ē (oxidized) Cu 2+(aq) + 2ē → Cu(s) (reduced) Zn(s) + Cu 2+(aq) → Zn 2+(aq) + Cu(s) 2015 -16

Foundation Year Program Standard cell potential • The standard cell potential represents the difference between standard reduction potentials of half-cells. or 2015 -16

Foundation Year Program Standard cell potential Zn(s) → Zn 2+(aq) + 2ē (oxidized) Cu 2+(aq) + 2ē → Cu(s) (reduced) 2015 -16

Foundation Year Program Standard cell potential • Greater the value of cell potential higher the energy produced by cell. → The choice of electrode substance determines the property of electrochemical cell, hence the performance of battery. 2015 -16

Foundation Year Program Applications of electrochemistry: Electroplating • The process of coating an electrically conductive object with a thin layer of metal using an electrical current. • Used to give a metal particular properties or for aesthetic reasons: Ø abrasion and wear resistance Ø the production of jewellery 2015 -16

Foundation Year Program Electroplating 2015 -16

Foundation Year Program Electroplating/Silver Plating a Spoon • At anode (+ve), actual silver metal Ag(s) → Ag+(aq) + e- • At cathode (-ve), spoon: Ag+(aq) + e- →Ag(s) 2015 -16

Foundation Year Program Applications of electrochemistry: The chloralkali industry • Produces chlorine and sodium hydroxide through the electrolysis of the raw material brine (a saturated solution Na. Cl that is obtained from natural salt deposits). 2 Na. Cl(aq) + 2 H 2 O(l) ==> H 2(g) + Cl 2(g) + 2 Na. OH(aq) 2015 -16

Foundation Year Program The chloralkali industry 2015 -16

Foundation Year Program The chloralkali industry • At anode (+ve): 2 Cl−(aq) → Cl 2(g) + 2 e • At cathode (-ve): 2 H 2 O(l) + 2 e− → H 2(g) + 2 OH−(aq) • Overall: 2 Cl−(aq) + 2 H 2 O(l) → Cl 2(g) + H 2(g) + 2 OH−(aq) 2015 -16

Foundation Year Program The products THREE major products formed during this electrolysis: • Hydrogen gas • Chlorine gas • Sodium hydroxide in aqueous solution In many modern industrial chemistry plants some of these products are further reacted ‘on site’ to form other useful chemicals. 2015 -16

Foundation Year Program Use of products of chloralkali industry Chlorine is used: Water purification Disinfectant Paper production Medicine Sodium hydroxide is used: Soap & cleaning agents Rayon Purify bauxite 2015 -16

Foundation Year Program Applications of electrochemistry: Extraction of metals 2015 -16

Foundation Year Program Applications of electrochemistry: Protection from corrosion Electrochemical Corrosion of Iron 2015 -16

Foundation Year Program Applications of electrochemistry: Protection from corrosion Cathodic Protection 2015 -16

Foundation Year Program Applications of electrochemistry: Green synthesis of organic compounds Electrosynthesis of organic compounds are more ecologically friendly and cheaper alternatives to traditional chemical reactions. 2015 -16

Foundation Year Program Applications of electrochemistry: Batteries 2015 -16

Foundation Year Program Battery of new era https: //www. youtube. com/watch? v=Du. BS-p 2 ty. OU 2015 -16