Question

What are spectator ions ?

Answer 1

Hint: Spectator ions are present in a solution but don't take part in a solution's chemical reaction as its name suggests. When reactants dissociate into ions, some of the ions may combine to form a new compound and there are other ions that don't take part in this chemical reaction.

Complete answer:
Let us take some examples of solutions in order to understand the actual meaning of spectator ions.
The positively-charged silver cation was placed first on the reactant side of the net ionic equation, followed by the negatively-charged chloride anion. In general, if the molecular equation is appropriately balanced, the net ionic equation will be balanced by both mass and charge.
As a result, a spectator ion may be seen in the reaction of aqueous sodium carbonate and copper(II) sulphate, but it has no effect on the equilibrium.
 $ 2~Na{{+}_{(aq)}}~+~C{{O}_{3}}{{^{2-}}_{(aq)}}~+~C{{u}^{2+}}_{(aq)}~+~S{{O}_{4}}{{^{2-}}_{(aq)}}~\to \text{ }2~N{{a}^{+}}_{(aq)}~+~S{{O}_{4}}{{^{2-}}_{(aq)}}~+~CuC{{O}_{3}}_{(s)} $
Because they stay constant on both sides of the equation, 4 ions are called spectator ions. The term comes from the fact that they just "watch" how the other ions respond. They are used to balance the charges of the ions in total ionic equations. Whereas the $ C{{u}^{2+}} $ and $ C{{O}_{3}}^{2-} $ ions combine to produce a solid $ CuC{{O}_{3}} $ precipitate. Spectator ions are eliminated from a full ionic equation to create a net ionic equation in reaction stoichiometry.
 $ ~2~{{a}^{+}}_{(aq)}~+~C{{O}_{3}}{{^{2-}}_{(aq)}}~+~C{{u}^{2+}}_{(aq)}~+~{{}_{4}}{{^{2-}}_{(aq)}}~\to ~2~{{a}^{+}}_{(aq)}~+~{{}_{4}}{{^{2-}}_{(aq)}}~+~CuC{{O}_{3}}_{(s)}~ $
Hence $ ~~C{{O}_{3}}{{^{2-}}_{(aq)}}~+~C{{u}^{2+}}_{(aq)}~~\to ~~CuC{{O}_{3}}_{(s)}~ $
In a chemical equation, a spectator ion is an ion that may function as both a reactant and a product bite don't take part in the chemical reaction.

Note:
Only the Debye length is affected by the concentration of spectator ions. Potential determining ions, on the other hand, are ions whose concentrations impact both the surface potential and the Debye length (through surface chemical processes). The spectator ions in the original equation are ignored in a net ionic equation. As a result, the net reaction differs from the total ionic reaction.