Explain with example how oxidation number helps us to balance a chemical reaction ?
Explain with example how oxidation number helps us to balance a chemical reaction ?
Before we will get to explanation very important disclaimer: oxidation numbers don't exist. They were invented to help in charge accounting needed when balancing redox reaction equations, but they don't refer to any real life chemical concept.
The general idea behind the oxidation numbers (ON) method for balancing chemical equations is that electrons are transferred between charged atoms. These charges - assigned to individual atoms - are called oxidation numbers, just to remind you that they don't reflect real structure of the reagents.
There are several simple rules used for assigning oxidation numbers to every atom present in any compound:
- First of all, charged mono atomic ion has oxidation number equal to its charge. Thus Na+ has oxidation number +1, Fe3+has oxidation number +3, F- has oxidation number of -1 and S2- has oxidation number of -2.
- Second rule says that the oxidation number of a free element is always 0. Thus oxidation number of solid, metallic Cu is 0, oxidation number of O in O2 is 0, the same holds for S in S8 and so on.
- Oxygen in almost all compounds has oxidation number -2.
- Hydrogen in almost all compounds has oxidation number +1.
- Some elements usually have the same oxidation number in their compounds:
- alkali metals - Li, Na, K, Rb, Cs - oxidation numbers are +1
- alkaline earth metals - Be, Mg, Ca, Sr, Ba - oxidation numbers are +2
- halogens (except when they form compounds with oxygen or one another) - oxidation numbers are -1 (always true for fluorine)
- Last rule says that the charge of the ion or molecule equals sum of oxidation numbers of all atoms.
There are some exceptions to the rules 3 and 4 - for example oxygen in peroxides has oxidation number of -1, it is also not -2 in compounds with fluorine (where F is always -1), hydrogen in hydrides has oxidation number -1.
Before we will get to explanation very important disclaimer: oxidation numbers don't exist. They were invented to help in charge accounting needed when balancing redox reaction equations, but they don't refer to any real life chemical concept.
The general idea behind the oxidation numbers (ON) method for balancing chemical equations is that electrons are transferred between charged atoms. These charges - assigned to individual atoms - are called oxidation numbers, just to remind you that they don't reflect real structure of the reagents.
There are several simple rules used for assigning oxidation numbers to every atom present in any compound:
- First of all, charged mono atomic ion has oxidation number equal to its charge. Thus Na+ has oxidation number +1, Fe3+has oxidation number +3, F- has oxidation number of -1 and S2- has oxidation number of -2.
- Second rule says that the oxidation number of a free element is always 0. Thus oxidation number of solid, metallic Cu is 0, oxidation number of O in O2 is 0, the same holds for S in S8 and so on.
- Oxygen in almost all compounds has oxidation number -2.
- Hydrogen in almost all compounds has oxidation number +1.
- Some elements usually have the same oxidation number in their compounds:
- alkali metals - Li, Na, K, Rb, Cs - oxidation numbers are +1
- alkaline earth metals - Be, Mg, Ca, Sr, Ba - oxidation numbers are +2
- halogens (except when they form compounds with oxygen or one another) - oxidation numbers are -1 (always true for fluorine)
- Last rule says that the charge of the ion or molecule equals sum of oxidation numbers of all atoms.
There are some exceptions to the rules 3 and 4 - for example oxygen in peroxides has oxidation number of -1, it is also not -2 in compounds with fluorine (where F is always -1), hydrogen in hydrides has oxidation number -1.
