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Net Ionic Equations

Write molecular, complete ionic and net ionic equations; check atoms, charge and states.

AP Chemistry Topic 4.2 · CED printed p. 79 / PDF p. 86. This teaching, practice and feedback were added for the AP edition; original author material remains separately traceable.

Before you start

An equation can describe a physical process too: H2O(l) → H2O(g) preserves identity while changing phase. For dissolution, NaCl(s) → Na+(aq) + Cl−(aq) shows separated, hydrated ions, not floating NaCl molecules. State labels tell you which representation is appropriate; they are part of the explanation.

For a chemical reaction, change coefficients until every element has the same atom count on both sides. Do not edit subscripts: changing H2O to H2O2 changes the substance. Charge is a second independent check. An equation may conserve atoms but still create net charge, so count both. Balanced coefficients describe relative numbers or moles of chemical units, not relative masses.

A molecular equation records reagent formulas. A complete ionic equation separates dissolved strong electrolytes into ions. Keep solids, liquids, gases, and weak acids or bases as intact species; writing every aqueous formula as free ions would falsely claim complete ionization. Cancel a spectator only when the same species, charge, phase, and amount occur on both sides. The net ionic equation focuses on the actual change. For a weak acid neutralized by hydroxide, HA(aq) + OH−(aq) → A−(aq) + H2O(l), HA stays together on the left.

Let's work through it

Given that AgCl is sparingly soluble, represent mixing AgNO3(aq) and NaCl(aq).

  1. Molecular: AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq). The sodium and nitrate salts stay dissolved.
  2. Complete ionic: Ag+ + NO3− + Na+ + Cl− → AgCl(s) + Na+ + NO3−, with (aq) on every free ion.
  3. Cancel Na+ and NO3−. Net ionic: Ag+(aq) + Cl−(aq) → AgCl(s). Check: one Ag and one Cl each side, and total charge zero each side.

Try it from memory

Pause & retrieve

Try it before you peek.

Write your answer and the reason from memory. Then compare with the worked answer. Your self-assessment is a study decision, not an automatically graded score.

Question 1 of 20 self-assessed

Question 1

Why is AgCl(s) not split into Ag+(aq) and Cl−(aq)?

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Retrieval 1

Why is AgCl(s) not split into Ag+(aq) and Cl−(aq)?

Worked answer and reason

The observed solid consists of an ionic lattice. Splitting it into aqueous ions would erase the precipitation being represented.

Physical state determines whether ions are separate in solution.

Retrieval 2

Write vaporization of ethanol, C2H5OH.

Worked answer and reason

C2H5OH(l) → C2H5OH(g). Its composition stays fixed.

Physical processes still have symbolic representations.

Catch the tempting mistake

All aqueous substances split completely into ions.
Aqueous means dissolved. Weak acids and bases mostly retain molecular identity, so preserve them in a net ionic equation.
Changing a subscript is a valid way to balance atoms.
Subscripts identify species; coefficients change how many units participate.

Put it to work

Give the chemical reason as well as the calculation. Worked solutions are on a separate page.

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For the teacher
  • Require state labels and a separate charge sum.
  • Use a weak acid next to a strong acid to check that students understand dissociation.

Unit planning and formative guidance →

Source objectives and scope

Source edition: ap-chemistry-ced-fall2024-local-b5dfe867. See this topic in the course outline →

4.2.A
Represent changes in matter with a balanced chemical or net ionic equation: i. For physical changes. ii. For given information about the identity of the reactants and/or product. iii. For ions in a given chemical reaction.
4.2.A.1
All physical and chemical processes can be represented symbolically by balanced equations.
4.2.A.2
Chemical equations represent chemical changes. These changes are the result of a rearrangement of atoms into new combinations; thus, any representation of a chemical change must contain equal numbers of atoms of every element before and after the change occurred. Equations thus demonstrate that mass and charge are conserved in chemical reactions.
4.2.A.3
Balanced molecular, complete ionic, and net ionic equations are differing symbolic forms used to represent a chemical reaction. The form used to represent the reaction depends on the context in which it is to be used.
Science references for this teaching
Glossary and deeper reading · 7 refreshers

These editorial refreshers supplement the reading. Definitions and examples are added guidance; original source wording and recorded answers remain in their original context.

  • Mole

    A mole is an amount of substance containing exactly 6.02214076 × 10²³ specified entities. The entities can be atoms, molecules, ions, or formula units, so the counted entity must be named. For example, one mole of oxygen molecules contains two moles of oxygen atoms.

    Read more: Moles and Molar Mass →

  • Molarity

    Molarity is the amount of a solute in moles divided by the final solution volume in liters. It describes concentration rather than the total amount of solute. For example, 0.10 mole dissolved to make 0.50 liter of solution gives a molarity of 0.20 mole per liter.

    Read more: Solutions and Mixtures →

  • Molecular formula

    A molecular formula gives the actual number of each kind of atom in a molecule. It can be a whole-number multiple of the empirical formula. For example, glucose has molecular formula C₆H₁₂O₆ and empirical formula CH₂O.

    Read more: Elemental Composition of Pure Substances →

  • Ideal gas law

    The ideal gas law relates pressure, volume, amount, and absolute temperature in an idealized gas model. It treats particles as having negligible volume and no intermolecular attractions. For example, at fixed amount and temperature, doubling the container volume halves the ideal gas pressure.

    Read more: Ideal Gas Law →

  • Ion

    An ion is an atom or group of atoms with a net electric charge. Ordinary ion formation changes electron count without changing the element's proton count. For example, a sodium atom losing one electron becomes a sodium ion with charge +1.

    Read more: Valence Electrons and Ionic Compounds →

  • Electrolyte

    An electrolyte forms mobile ions when dissolved and can allow a solution to conduct electric current. Strong and weak electrolytes differ in the extent to which dissolved species form ions under the stated conditions. For example, dissolved sodium chloride supplies sodium and chloride ions to water.

    Read more: Representations of Solutions →

  • Weak acid or base

    A weak acid or base reacts only partially with water and establishes an equilibrium. Its equilibrium constant describes strength, while analytical concentration describes how much was prepared per volume. For example, acetic acid leaves both acid molecules and its conjugate base in water.

    Read more: Weak Acid and Base Equilibria →

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