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Unformatted text preview: Page 1 Raffles Junior College Raffles Junior College Raffles Junior College Raffles Junior College Chemistry Olympiad Chemistry Olympiad Chemistry Olympiad Chemistry Olympiad Notes Notes Notes Notes Electrochemistry Electrochemistry Electrochemistry Electrochemistry A REDOX PROCESSES AND ELECTROLYTES 1. Oxidation is defined as (a) loss of electron(s) (b) increase in oxidation number 2. Reduction is defined as (a) gain of electron(s) (b) decrease in oxidation number 3. A redox reaction is one in which both oxidation and reduction occurs. 4. An equation for a redox reaction may be separated into two - equations: eg for the redox reaction: Cu 2+ (aq) + Zn (s) Cu (s) + Zn 2+ (aq) Oxidation - equation: Zn (s) Zn 2+ (aq) + 2e- Reduction - equation: Cu 2+ (aq) + 2e- Cu (s) 5. An oxidising agent is one which oxidises another. In a redox reaction, the oxidising agent is itself reduced (gains e- ). 6. A reducing agent is one which reduces another. In a redox reaction, the reducing agent is itself oxidised (loses e- ). 7. Electrochemistry deals with the relationship between electricity and chemical reactions . Since electricity involves the flow of electrons, electrochemistry focuses on redox reactions. 8. Some everyday examples of redox reactions: (a) rusting (b) respiration and combustion (c) batteries and cells (d) extraction of ores (eg aluminium from bauxite) (e) electroplating Page 2 Some Key Terms : Electrolyte (a) An electrolyte is a compound which will conduct an electric current and be decomposed by it when in aqueous solution or in the molten state. An electrolyte conducts electricity due to the flow of charge carried by its ions . (b) A strong electrolyte is a compound which is fully ionised when molten or in solution. All ionic compounds are strong electrolytes since they are made up of ions which become mobile in the molten or aqueous state. Some covalent compounds such as HCl and HNO 3 ionise completely in water and are also strong electrolytes. Examples of strong electrolyte: NaOH, lead(II) chloride, hydrogen chloride. (c) A weak electrolyte is a compound which only partially ionises when molten or in solution. Examples: water, aqueous ammonia, most organic acids and organic bases (d) A non-electrolyte does not ionise at all and does not conduct electricity. Examples: Most organic compounds such as hydrocarbons (eg methane, ethene, benzene), alcohols, sugars, halogenoalkanes (eg chloromethane). Electrode Potentials Important information: 1. Existence of electrode potential of a metal placed in an aqueous solution of its ions: (a) Metal atoms may lose electrons and go into solution: M (s) M n+ (aq) + ne (b) Metal ions from solution may gain electrons and form the metal: M n+ (aq) + ne M (s) (c) An equilibrium is established between the metal and its ions: M n+ (aq) + ne M (s) (d) (For a metal that is more easily oxidised) There is a (i) build up of e on the metal surface ....
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This note was uploaded on 10/12/2010 for the course C 11 taught by Professor Na during the Spring '10 term at Rappahannock Community College.
- Spring '10