Question

Can you describe the advantages involved in expressing double displacement reactions with net ionic equations rather than with total ionic equations?

Answer 1

The advantage of net ionic equations is that they show only those species that are directly involved in the reaction.

Explanation:

Consider the reaction between silver nitrate and sodium chloride.

AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)

The ionic equation is

Ag⁺(aq) + NO₃⁻(aq) + Na⁺(aq) + Cl⁻(aq) → AgCl(s) + Na⁺(aq) + NO₃⁻(aq)

The net ionic equation is

Ag⁺(aq) + Cl⁻(aq) → AgCl(s)

The net ionic equation tells us that only the Ag⁺ ions and the Cl⁻ ions are needed to form AgCl.

The Na⁺ and NO₃⁻ ions are there only to balance the charges. They do not take part in the reaction. They just watch as spectators while the Ag⁺ and Cl⁻ ions do their thing. That's why we call them spectator ions.

The net ionic equation tells us that all we need to prepare AgCl is a source of Ag⁺ ions and of Cl⁻ ions. We don't have to use just AgNO₃ and NaCl.

We can another soluble silver salt as a source of Ag⁺ ions, such as silver acetate.

We can use any soluble chloride as a source of Cl⁻ ions, such as KCl, CaCl₂, or HCl.

Any combination of these will form a white precipitate of AgCl by the same net ionic reaction.