complete ionic equation
Summary
A complete ionic equation writes every strong electrolyte in a reaction as separate ions in aqueous solution, while solids, liquids, gases, and weak electrolytes stay as whole formulas. Cancelling the spectator ions, which appear unchanged on both sides, gives the net ionic equation.
Detail
Meaning: A complete (full) ionic equation shows the species actually present in solution. Start from a balanced molecular equation, then split into ions every aqueous strong electrolyte: soluble ionic salts, strong acids (HCl, HNO₃, H₂SO₄ for its first dissociation), and strong bases (group 1 hydroxides, and Ba(OH)₂, Ca(OH)₂ as dissolved). Keep as intact formulas the precipitates (s), liquids such as H₂O (l), gases (g), and weak acids or bases, which ionize only slightly.
Example: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq) becomes Ag⁺(aq) + NO₃⁻(aq) + Na⁺(aq) + Cl⁻(aq) → AgCl(s) + Na⁺(aq) + NO₃⁻(aq).
Equation: Coefficients multiply the ions in each formula, so 2 Al(NO₃)₃ gives 2 Al³⁺ + 6 NO₃⁻. Both atoms and total charge must balance.
On the MCAT: Passages on precipitation, acid-base neutralization, or solubility ask you to identify spectator ions, write the net ionic equation, or decide which species remain in solution. Use the solubility rules to decide what precipitates. Charge balance is a quick check on an answer.
Common confusion: Students split everything, including solids and weak acids. Splitting is only for aqueous strong electrolytes. For example, acetic acid stays as CH₃COOH in the equation because it is mostly undissociated. Also, the complete and net ionic equations differ: the net one omits spectator ions.
Sources
- Chemistry: The Central Science
- Chemistry
- General Chemistry: Principles and Modern Applications
Written for the MCAT and checked before it was published. For study reference only. Spotted an error? Let us know.