Papa Smurf's Chemistry Lessons

Balancing Ionic Equations :) 

In some cases chemists prefer to use ionic equations instead of the normal equation. Ionic equations are simpler than the full equations that show the full formulae of the compound.

As a first example I will use zinc granules that react with aqueous copper(II) sulfate to produce copper metal and a red-brown deposit of zinc sulfate. The full equation for this is: Zn(s) + CuSO4(aq) -> ZnSO4(aq) + Cu(s).

During this reaction copper ions Cu²⁺ are converted into copper atoms by gaining 2 electrons and Zn atoms are converted into Zn²⁺ ions by losing 2 electrons. The sulphate ions remain unchanged; they are spectator ions. However, the ionic equation does not show the ions that remain unchanged. It therefore provides a shorter equation which focuses our attention on the change that is taking place: Zn(s) + Cu²⁺(aq) --> Zn²⁺(aq) + Cu(s).

In an ionic equation we must balance an overall charge on the ions on each side of the equation. Notice that the charge on each side of this ionic equation is 2+. Ensure that the charges are balanced before balancing the number the number of atoms of each element.

The reaction of  Cu²⁺(aq) with Zn(s) involves transfer of electrons. It is known as REDOX. Redox is a reaction which involves reduction and oxidation processes. Ionic equations are often used for redox reactions. Chemists also prefer to use ionic equations for PRECIPITATION. Precipitate is an insoluble solid formed when two solids react, e.g. white silver chloride formed when silver nitrate is added to sodium chloride solution.  For example, when sodium hydroxide is added dropwise to copper(II) sulfate a pale blue precipitate of copper(II) hydroxide,             Cu(OH)₂(s), is formed. The full equation is: CuSO₄(aq) + 2NaOH(aq) à Cu(OH)₂(s) + Na₂SO₄(aq).

The ionic equation is: Cu²⁺(aq) + 2OH^-(aq) à Cu(OH)₂(s).

Both sodium ions, Na⁺(aq), and sulfate ions, SO₄^2-(aq), are spectator ions, meaning they are unchanged and can be omitted.