Balancing Equations - Acidic and Basic Solutions

When we take in account reactions that are acidic or basic, we must consider the hydrogen ion and hydroxide ion. The overall approach regarding balancing these equation is very similar to a simple reaction, however, few more steps are required.

1. Write the unbalanced equation that show the formulas of the given reactants and products.
2. Balance the atoms other than oxygen and hydrogen.
3. Balance the atoms of Oxygen by adding water.
4. Balance the hydrogen atoms by adding hydrogen ions. (At this point, if we are dealing with an acidic solution, balance the charges by adding the electrons.)
5. If we are dealing with a basic solution: Add to both sides, the same number of hydroxide ions as the number or hydrogen ions present.
6. Add the hydrogen and hydroxide ions on the same side to form water.
7. Cancel and water molecule present on both sides of the reaction.
8. Balance the charges by adding the electrons.

Redox Reactions

Law of Conservation of Energy:

No energy is created, nor destroyed, it is transformed or transferred.

Yes, and in a chemical reaction? aren't there like several exchange of electrons?

If each atom or ion of a chemical reaction is oxidized, that another must be reduced. When this happens we have a redox reaction.

Redox reactions are not a type of reaction, like formation, or decomposition. 

Actually, all the types of reactions may be redox reactions.

To understand this concept better let's use this simple single-replacement reaction:

Zn(s)+CuSO4(aq)=Cu(s)+ZnSO4(aq)

Lets take away the spectators, which, in this case are the SO4 ions.

You obtain 

Zn(s) + Cu+2(aq) = Cu(s)+Zn+2 

As you see, Zinc lost electrons, it became positive, thus got oxidized. Copper, gained two electrons, since it was a cation and became a single atom. Therefore it was reduced. 

Well, we know that the electrons ran away from Zn to Cu, so what do we do about it?

Zinc is called the reducing agent, the one that donated electron, and the one the underwent oxidation, while copper is the oxidizing agent, the one that accepeted electrons, undergoes reduction.

Reduction

So, do you remember that little law of thermodynamics? What was it?

Energy is never created, or destroyed, it is always transformed...

...or transferred. 

When one atom, ion, or molecule, loses a electron, this little particle cannot just run around the environment. He needs a place to stay, a house. And what kind of house am i talking about?

Another atom, ion, or molecule.

Yes, they must gain the electrons that were lost by other elements that got oxidated. 

If oxidation is the loss of electrons, than, the gain of them is called reduction.

Oxidation

Okay! So, now let's look a little bit forward onto chemical reaction.

Our first topic is Oxidation.

Back in the days, chemists believed that oxidation was any reaction that occurred between any atom or compound with a molecular oxygen. 

However, after many and many years of study and analysis, it was learned that same reaction between atoms or compounds with other elements have similarities with those reaction involving oxygen. 

So the scientist came out with another definition for oxidation, which is the loss of electrons by an atom or an ion.

For example, when Mg(s) reacts with Cl2(g), our little buddy Magnesium atom loses electrons, becoming a cation. We can say, therefore, that Magnesium got oxidised.