Redox
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What it a redox reaction
Where oxidation and reduction occurs at same time
Oxidation is … Reduction is …
Oxidation is loss of electrons Reduction is gain of electrons
How do you know if something is being oxidised
The oxidation number increased Eg Fe2+ —> Fe3+
Write the half equation for Fe2+ oxidised into Fe3+
Fe2+ —> Fe3+ + e-
How do you know something is being reduced
Oxidation number decreases Eg Cr2O7^2- has ox number of +6 Cr3+ has oxidation number of 3+ Cr2O7^2- ~~~> Cr3
Balance Cr2O7^2- ~~~> Cr3
14H^+ + Cr2O7^2- + 6e- ~~~> 2Cr3 + 7H2O
Steps to balance redox
1) find ox n.o 2) find what’s being ox and red 3) write out ox and red equations 4) balance elements other than hydrogen and oxygen 5) balance oxygen with H2O 6) balance hydrogen with H+ 7) find overall charges 8) Add e- to balance charges 9) add coefficient by multiplying to get same number of e- 10) cancel like terms 11) combine half equations
What is disproportination
Atoms of the same element can both be oxidised and reduced
State in terms of electrons the meaning of oxidising agent
Electron acceptor
Oxidation number for uncombined element
Always 0 Eg Cl2 Fe O2
Ox number for ions
Always the same as the ions charge Eg Cl- = -1 Ca2+ = +2
Ox number for group 1
Always +1
Ox number for group 2
Always +2
Ox number for aluminium
Always 3+ Eg al2o3
Hydrogen
Always +1 Except in metal hydrides eg NaH where it’s -1
Ox number jn chlorine
Always -1 Unless if in compound with F and O - it would have postive value Eg in cl has a value of +3 in ClF3
Ox number in fluorine
Always -1
Ox number of oxygen
Always -2 Unless in peroxides where it’s -1 EG in H2O2 it’s -1 Peroxide means for every oxygen And +2 in OF
Group 7 Elements have an oxidation state of -1 unless
They are in a compound w fluorine. Here they have an ox state of +1