Topic 10 and 19 – Oxidation and Reduction
Anode: Where oxidation takes place. In electrolysis, it is the + electrode and anions are attracted here.
Cathode: Where reduction takes place. In electrolysis, it is the – electrode and cations are attracted here.
Electrolysis: Passage of electric current through an electrolyte. Amount of discharge is affected by: 1) current; 2) charge on ion, 3) duration of electrolysis.
Electrolyte: A substance which does not conduct electricity when solid, but does when molten or in aqueous solution and is chemically decomposed in the process.
Electrolytic cell: Used to make non-spontaneous redox reactions occur by providing energy in the form of electricity from an eternal source.
Electroplating: A process of coating one metal with a thin layer of another metal, by electrolysis.
Half cell: A metal in contact with an aqueous solution of its own ions.
Oxidation number: Ox. no. of:a) elements: 0; b) ion: its charge; c) oxygen: -2 (except in peroxides, -1); d) hydrogen: +1 (except metal hydrides, -1); e) fluorine: -1.
Oxidation: The loss of e-, the gain of oxygen, the loss of hydrogen or the increase in oxidation number.
Oxidizing agent: A substance that readily oxidizes other substances. Oxidizing agents are thus reduced. The higher the oxidation number, the better an oxidizing agent it is, generally.
Reactivity: A measure of the readiness of a substance to gain or lose e.. The stronger the reducing agent or oxidizing agent, the more reactive it is.
Redox reaction: A reaction in which there is a transfer of e-, i.e. reduction and oxidation occurring simultaneously.
Reducing agent: A substance that readily reduces other substances. Reducing agents are thus oxidized.
Reduction: The gain of e-, the loss of oxygen, the gain of hydrogen or the decrease in oxidation number.
Salt bridge: Allows the free movement of ions in a voltaic cell. Paper dipped in a saturated solution of KNO3 is an example of a salt bridge.
Shorthand notation: For a voltaic cell. Example: Cu(s)/Cu2+(aq) || H+(aq) / H2(g)
Standard conditions: 298 K, 1 atm, 1.0 M.
Standard electrode potential: Measuring a potential cannot be done as this interferes with the system being investigated. However, the electrode potential of one half cell can be compared against another half-cell, by convention, the hydrogen half-cell, which is arbitrarily given a value of 0 V.
Standard electromotive force: Difference between the two standard electrode potentials of the two half cells. Ecell
Standard hydrogen electrode: Arbitrarily assigned a potential of zero. Electrode consists of an inert metal such as platinum dipped into a 1 M solution of HCl, where hydrogen gas at 1 atm flows in. Platinum black, a very finely divided platinum, catalyzes the electrode equilibrium.
Voltaic cell: Two different half-cells connected together to enable to e- transferred during the redox reaction to produce energy in the form of electricity. The e- are produced at the half-cell that is most easily oxidized.