What is Oxidation?
The Process of electron loss.
What is Oxidation?
The Process of electron gain.
What are the rules for assigning oxidation numbers?
- All uncombined elements have an oxidation number of zero
- The oxidation numbers of the elements in a compound add up to zero
- The oxidation number of a monoatomic ion is equal to the ionic charge
- In a polyatomic ion (CO32-) the sum of the individual oxidation numbers of the elements adds up to the charge on the ion
- Several elements have invariable oxidation numbers in their common compounds.
eg . Zn, Cl2, O2, Ar all have oxidation numbers of zero
In NaCl Na= +1 Cl= -1 Sum = +1 -1 = 0
e.g. Zn2+ = +2 Cl- = -1
e.g. in CO32- C = +4 and O = -2 sum = +4 + (3 x -2) = -2
What is the oxidation number of Group 1 metals?
+1
What is the Oxidation number of Group 2 metals?
+2
What is the Oxidation number for Al?
+3
What is the Oxidation number for H?
+1 (except in metal hydrides where it is –1 eg NaH)
What is the Oxidation number for F?
-1
What is the Oxidation number of Cl, Br, and I?
–1 except in compounds with oxygen and fluorine
What is the Oxidation number of 0?
-2 except in peroxides (H2O2 ) where it is –1 and in compounds with fluorine.
What is the Oxidation number of Fe in FeCL3?
Using rule 5, Cl has an O.N. of –1
Using rule 2, the O.N. of the elements must add up to 0
Fe must have an O.N. of +3
in order to cancel out 3 x –1 = -3 of the Cl’s
What does a reduction half equation show?
A reduction half equation only shows the parts of a chemical equation involved in reduction. The electrons are on the left
What does an Oxidation half equation show?
An oxidation half equation only shows the parts of a chemical equation involved in oxidation.
The electrons are on the right
What is a reducing agent?
Electron donors
What is an oxidising agent?
Electron acceptors
What does an oxidising agent do?
An oxidising agent (or oxidant) is the species that causes another element to oxidise. It is itself reduced in the reaction.
What does a reducing agent do?
A reducing agent (or reductant) is the species that causes another element reduce. It is itself oxidised in the reaction.
How do you write half equations?
- Work out oxidation numbers for element being oxidised/ reduced
- Add electrons equal to the change in oxidation number For reduction add e’s to reactants
For oxidation add e’s to products - check to see that the sum of the charges on the reactant side equals the sum of the charges on the product side
If the substance that is being oxidised or reduced contains a varying amount of O then the half equations are balanced by adding…
H+, OH- ions and H2O.
What must there be to combine half equations?
To combine two half equations there must be equal numbers of electrons in the two half equations so that the electrons cancel out
