Redox Titration Lab - R e d o x R e a c t i ons OXID A TION...

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Redox Reactions OXIDATION AND REDUCTION 11.1 At the end of this worksheet you should know 1. An oxidising agent is a substance, which accepts electrons; a reducing agent is a substance, which donates electrons. 2. Oxidising and reducing agents can be identified in redox reactions. OXIDATION Oxidation is defined as a loss of electrons. e.g. iron rusting When iron metal is exposed to oxygen in the air the iron combines with the oxygen to form iron (II) oxide and further reacts to form iron(III) oxide Fe => Fe 2+ + 2e Fe 2+ => Fe 3+ + e REDUCTION Reduction is defined as a gain of electrons. e.g. Formation of copper from copper (II) oxide When hydrogen gas is passed over heated copper (II) oxide, the copper (II) oxide is reduced to copper metal. Cu 2+ + 2e => Cu Redox Redox reactions are a combination of reduction and oxidation, which occur simultaneously. e.g. Displacement of hydrogen from acidic solution with magnesium. Mg + 2H + => Mg 2+ + H 2 Redox Red Oxid OXIDISING AND REDUCING AGENTS An oxidising agent is an electron acceptor. An oxidising agent is reduced during a redox reaction. A reducing agent is an electron donor. A reducing agent is oxidised during a redox reaction. Al(s) + CuCl 2(aq) => AlCl 3(aq) + Cu(s) 2Al (s) + 3Cu 2+ => 2Al 3+ + 3Cu (s) Redox Cu 2+ + 2e => Cu (s) Red Al (s) => Al 3+ + 3e Oxid The reducing agent is ………………………………. The oxidising agent is ………………………………….. Note The spectator ions in the above reaction were…………………………………………….. Consider the cell opposite Zn (s) + Sn 2+ (aq) => Zn 2+ (aq) + Sn (s) Redox Red Oxid The reducing agent is ………………………………. The oxidising agent is ………………………………….. Redox equations 11.2 At the end of this worksheet you should know that 1. Ion-electron equations can be written for oxidation and reduction reactions. Zn(s) Sn(s) Zn 2+ (aq) Sn2 + (aq)
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2. Ion-electron equations can be combined to give redox equations 3. Given reactant and product species, ion electron equations, which include H+ (aq), and H 2 O [l] can be written. WRITING A BALANCED REDOX EQUATION In order to write a balanced redox equation for a reaction we have to i) write the ion-electron equation for the oxidation. ii) write the ion-electron equation for the reduction. iii) balance the number of electrons gained and lost. iv) add the oxidation and reduction reactions together. e.g. when magnesium is added to a solution of iron(III) nitrate the magnesium displaces the iron(III) ions from solution to form iron and magnesium nitrate. The ion-electron equation for the oxidation is:- The ion-electron equation for the reduction is:- To balance the number of electrons gained and lost we must multiply the oxidation reaction by 3 and the reduction reaction by 2 then add them together giving:- In the examples we have looked at so far the oxidation and reduction reactions have always been relatively easy to write in balanced form. However consider the reaction between acidified potassium dichromate solution and tin(II) chloride solution in which tin(II) ions are oxidised to tin(IV) ions and dichromate ions reduced to chromium(III) ions.
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