Question

What is a net ionic equation? What species are shown in such an equation, and which species are not shown?

Short answer

A net ionic equation is a simplified version of a chemical equation that only shows the species involved in the actual chemical reaction, focusing on the reactive species and eliminating spectator ions. Spectator ions are the ions that do not participate in the chemical reaction and remain unchanged, while reactive species directly participate in the reaction and form new products. To write a net ionic equation, first write the balanced molecular equation, then dissociate strong electrolytes into ions, discard spectator ions, and finally write the balanced net ionic equation using the remaining reactive species. For example, the net ionic equation for the reaction between sodium chloride (NaCl) and silver nitrate (AgNO3) is: Cl^- (aq) + Ag^+ (aq) -> AgCl (s).

Step-by-step solution

Definition of a Net Ionic Equation

A net ionic equation is a simplified version of a chemical equation that only shows the species involved in the actual chemical reaction. The purpose of writing a net ionic equation is to focus on the species that contribute to the reaction, eliminating the spectator ions that do not participate in the reaction. In other words, it showcases the species that change during the reaction but leaves out the ones that remain unchanged.

Spectator Ions Versus Reactive Species

It is important to understand the difference between strong and weak electrolytes to determine which species appear in the net ionic equation. A strong electrolyte, like a soluble ionic salt, dissociates completely in water, becoming ions in solution. These ions can be further divided into two types: 1. Spectator ions – These are the ions that do not participate in the chemical reaction, remaining unchanged throughout the process, and hence are not included in the net ionic equation. 2. Reactive species – These are the ions that directly participate in the chemical reaction, leading to the formation of a new product, and are included in the net ionic equation. Weak electrolytes generally do not dissociate completely in water, and their ions typically remain bonded together in solution. Therefore, weak electrolytes are usually not included in net ionic equations.

How to Write a Net Ionic Equation

To write a net ionic equation, follow these steps: 1. Write the balanced molecular equation. 2. Identify and dissociate all strong electrolytes, writing the constituents as ions. 3. Discard the spectator ions to obtain only the reactive species. 4. Write the balanced net ionic equation using the remaining reactive species.

Example of a Net Ionic Equation

Let's consider the following reaction between sodium chloride (NaCl) and silver nitrate (AgNO3): NaCl (aq) + AgNO3 (aq) -> NaNO3 (aq) + AgCl (s) Step 1: The molecular equation is already balanced: NaCl (aq) + AgNO3 (aq) -> NaNO3 (aq) + AgCl (s) Step 2: Dissociate strong electrolytes into ions: Na^+ (aq) + Cl^- (aq) + Ag^+ (aq) + NO3^- (aq) -> Na^+ (aq) + NO3^- (aq) + AgCl (s) Step 3: Discard spectator ions, which in this case are Na^+ and NO3^-: Cl^- (aq) + Ag^+ (aq) -> AgCl (s) Step 4: Write the balanced net ionic equation: Cl^- (aq) + Ag^+ (aq) -> AgCl (s) Hence, the net ionic equation for the reaction between sodium chloride and silver nitrate is: Cl^- (aq) + Ag^+ (aq) -> AgCl (s)