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Starter w.c. 31.10.11. In the following redox reactions use oxidation numbers to explain what has been oxidised and what has been reduced: N 2 + 3H 2 2NH 3 3Mg + 2Fe(NO 3 ) 3 3Mg(NO 3 ) 2 + 2Fe MnO 2 + 4HCl MnCl 2 + Cl 2 + 2H 2 O. Answers
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Starter w.c. 31.10.11 In the following redox reactions use oxidation numbers to explain what has been oxidised and what has been reduced: N2 + 3H2 2NH3 3Mg + 2Fe(NO3)3 3Mg(NO3)2 + 2Fe MnO2 + 4HCl MnCl2 + Cl2 + 2H2O
Answers N2 + 3H2 2NH3 0 0 -3 +1 Nitrogen reduced: oxidation number decreases from 0 in N2to -3 in NH3; hydrogen oxidised: oxidation number increases from 0 in H2 to +1 in NH3 3Mg + 2Fe(NO3)3 3Mg(NO3)2 + 2Fe 0 +3 +5 -2 +2 +5 -2 0 Iron reduced: oxidation number decreases from +3 in Fe(NO3)3to 0 in Fe; magnesium oxidised: oxidation number increases from 0 in Mgto +2 in Mg(NO3)2
Answers c. MnO2+ 4HCl MnCl2 + Cl2 + 2H2O +4 -2 +1 -1 +2 -1 0 +1 -2 Manganese reduced: oxidation number decreases from +4 in MnO2to +2 in MnCl2; chlorine oxidised: oxidation number increases from -1 in HClto 0 in Cl2