To write a net ionic equation, follow these steps:
Start with a balanced chemical equation for the reaction in question. Ensure that the equation is balanced in terms of both atoms and charges.
Rewrite the balanced equation, explicitly indicating the physical states of the reactants and products (solid, liquid, gas, or aqueous solution) using appropriate symbols: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous.
Identify any strong electrolytes among the reactants and products. Strong electrolytes are substances that dissociate completely into ions when dissolved in water. They include strong acids, strong bases, and soluble ionic compounds.
Write the complete ionic equation by representing the strong electrolytes as their respective dissociated ions. Leave any weak electrolytes or insoluble substances in molecular form.
Identify the spectator ions, which are ions that are present on both sides of the equation and do not participate in the reaction.
Write the net ionic equation by eliminating the spectator ions. Include only the species that undergo a chemical change.
Here's an example to illustrate the process:
Let's consider the reaction between sodium chloride (NaCl) and silver nitrate (AgNO₃) to form silver chloride (AgCl) and sodium nitrate (NaNO₃):
Step 1: Write the balanced chemical equation: NaCl(aq) + AgNO₃(aq) → AgCl(s) + NaNO₃(aq)
Step 2: Rewrite the equation with state symbols: NaCl(aq) + AgNO₃(aq) → AgCl(s) + NaNO₃(aq)
Step 3: Identify strong electrolytes: NaCl(aq) and AgNO₃(aq) are strong electrolytes.
Step 4: Write the complete ionic equation: Na⁺(aq) + Cl⁻(aq) + Ag⁺(aq) + NO₃⁻(aq) → AgCl(s) + Na⁺(aq) + NO₃⁻(aq)
Step 5: Identify spectator ions: Na⁺(aq) and NO₃⁻(aq) are spectator ions.
Step 6: Write the net ionic equation: Cl⁻(aq) + Ag⁺(aq) → AgCl(s)
The net ionic equation is Cl⁻(aq) + Ag⁺(aq) → AgCl(s). This equation represents the essential chemical change occurring in the reaction, eliminating the spectator ions.