7 Oxidation, reduction and redox reactions

process of electron loss

electron acceptors so they gain electrons

process of electron gain

electron donors so they lose electrons

Oxidation Is the Loss of electrons Reduction Is the Gain of electrons

donate electrons

accept electrons

addition of oxygen loss of hydrogen

loss of oxygen addition of hydrogen

ions that dont undergo any change to their oxidation number

uncombined elements have oxidation state of 0 the sum of all oxidation states in a compound is 0 since all compounds are electrically nutreal elements just bonded to identical atoms like O2 and H2 have oxidation state of 0 the oxidation state of a simple ion like Na+ is the same as its charge in compound ions,the overall oxidation state is just the charge hydrogen = +1 (except in metal hydrides eg.NaH where it is -1) group 1 = always +1 group2 = always +2 group3 = 3+ group 5 = 3- group6 = 2- group7 = 1- Aluminium = always +3 oxygen = -2 (except in peroxides where it is -1, and the compound OF2 where it is +2) fluorine= always -1 chlorine= -1 (except with fluorine and oxygen where it has positive values)

the charge on an atom if it were a simple ion

hydrogen has an oxidation state of +1 ,make N your x (x) +(+1 x 3)=0 x+3=0 x= -3

x +(-2)=0 x=2+

2x+(-10)=0 2x=10 x= 5+

2x+ (-6)=0 2x=6 x=3+

x+(4)(+1)=+1 x+4=+1 x=-3

x + (4)(-2)=-2 x=+6

x + 4(2-)=-3 x=+5

1+x+(-6)=0 x+(-6)=-1 x=+5

• write down the species before and after a reaction • balance any atoms apart from oxygen and hydrogen(these will be dealt with later) • balance any oxygens with H20 • balance any hydrogens with H+ ions • balance charges with electrons (e −)

Fe2+ —> Fe3+ Fe2+ —> Fe3+ + e − MnO4- —> Mn2+ MnO4- —> Mn2+ + 4H2O MnO4- +8H+ —>Mn2+ +4H20 5e − + MnO4- + 8H+ —> Mn2+ + 4H2O (Fe2+ —> Fe3+ + e −) x5 5Fe2+ —-> 5Fe3+ + 5e − 5e − + MnO4- + 8H+ —> Mn2+ + 4H2O the electrons cancel out and you get 5Fe2+ + MnO4- +8H+ —>Mn2+ +4H20 + 5Fe3+