1) Assign the Oxidation Numbers
The Oxidation Number (ON) of an element is its charge. It is the number of electrons an element contains. This would be our basis on whether the element gained or lost electrons in chemical reactions. We can say that an element is in its Oxidation State when the element already has a specific ON.
Unlike with our previous examples, not all equations would already reveal the ON of each element. In actuality, equations would only be presented as is and we will be the ones assigning the ON. In order to properly delegate the ON of the elements or compounds, the following rules should be followed and observed. It is a general rule that the charges or the ON should be multiplied …show more content…
The reactant under Reduction (RedHrxn) is the one that gains electrons and therefore decreases in oxidation number, whilst in contrary Oxidation (OxHrxn) is where the reactant loses electrons causing an increase in oxidation number.
Using the Redox equation we assigned ON to, let’s find out the Half-reactions:
Mg0 + H+1Cl-1 Mg+2Cl2-1 + H20 First, scout out for the Spectator ion so that we can already cross it out of our equation. Seeing the Cl did not change at all, we can automatically say that it will not undergo either process. All we have now is Mg and H. To distinguish the two half-reactions, let’s use the mnemonics as a guide:
OIL RIG= “Oxidation Is Loss” and “Reduction Is Gain”
LEO = “Loss of Electrons is Oxidation” and GER = “Gain of Electrons is Reduction”
LEORA = “Losing Electrons is Oxidation… Reducing Agent”
GEROA = “Gaining Electrons is Reduction… Oxidising Agent In the equation, Mg’s charge changed from 0 to +2 whilst as for H, it changed from +1 to 0. From there, we can already see that it’s Mg who lost electrons and will therefore undergo Oxidation. Or in another perspective, H gained an electron so it will undergo Reduction.
OxHrxn: Mg0 Mg+2 RedHrxn: H+1 H20
3) Balance the number of atoms for each