Oxidation States - ES Flashcards
What are oxidation states
numbers which are assigned to each element in a molecule or ion by following a set of rules. They help us to see what is being oxidised and reduced
Why are oxidation states used to help redox reactions
they help us to extend the idea of redox reactions as covalent examples where complete electron transfer has not taken place but the reaction is still redox
e.g. C + O2 -> CO2
This is a redox reaction as carbon is getting oxidised but no becoming a 4+ ion as the product is a covalent molecule, we could say the carbon is getting oxidised because its oxidation state is increasing from 0 to +4
Why are oxidation states used
though many redox reactions involve complete electron transfer, sometimes (e.g. when forming covalent molecules) the transfer is not complete so oxidation states are used to work out what happened
Rules for oxidation states (O.S)
O.S of atoms in uncombined elements (Zn, O2, Cl2) = 0
For simple ions the O.S is he charge in the ion (Cl- = -1, O2- = -2, Fe2+ = +2)
Neutral molecules the O.S add up to 0
In ions the O.S add up to the overall charge on the ion
The O.S of hydrogen in all compounds (except metal hydrides) = +1
The O.S of oxygen in all compounds (except in peroxides and OF2) = -2
What is disproportionation in O.S
it is when one particular element is simultaneously oxidised and reduced
