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Net Ionic Equations

In this lesson you will master writing full ionic and net ionic equations.

 

Key Objectives:

  1. Explain which compounds fully dissociate in solution.

  2. Write full ionic and net ionic equations.

  3. Identify spectator ions in reactions.

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Prerequisite Knowledge:

  1. Be able to identify whether compounds are ionic or covalent.

  2. Recognize the formulas for simple acids.

  3. Understand the meaning of (s), (l), (g), and (aq) symbols.

  4. Know the oxidation states (charges) for monatomic ions and common polyatomic ions.

What are Ionic & Net Ionic Equations?

Ionic and Net Ionic equations are used to represent the actual state of particles both before and after a reaction occurs.  Specifically, they show whether each reactant and product is dissociated into separate ions, or whether each molecule remains whole or undissociated.

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Which Compounds Dissociate?

Dissolving Ionic Compounds

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Some ionic compounds like NaCl dissolve in water.  In this case, their state of matter is labeled as aqueous or (aq).

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When these ionic compounds are in their dissolved state, they dissociate into separate ions.  For example, when table salt (NaCl) dissolves the positive Na⁺ ions separate from the negative Cl⁻ ions.  Each ion is then surrounded by water molecules that help keep the ions apart as shown below.

Therefore, soluble ionic compounds, like salt dissolved in water, could be written with the individual ions separated from one another.

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NaCl (aq) → Na⁺(aq) + Cl⁻(aq)

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Dissolving Covalent Compounds

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Covalent compounds can also dissolve in water.  However, these compounds do not dissociate into separate particles.  For example, sugar can dissolve, but it stays intact as a glucose molecule (C₆H₁₂O₆) rather than separate carbon, oxygen and hydrogen atoms.  

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An Important Exception:  Dissolved Acids

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In general covalent compounds do not dissociate into ions.  However, covalent compounds which are acids are exceptions to the rule.  You will recognize that a compound is an acid in a reaction because its formula will usually start with H.  For example, the following compounds are all acids:  HCl, HF, HNO₃, and HC₂H₃O₂.  

 

The amount of dissociation of an acid in water depends on whether it is "strong" or "weak."  The terms strong acid and weak acid have nothing to do with how deadly the acid is or concentrated the acid may be.  Instead, the terms strong and weak refer to the extent to which the compound dissociates.

 

Strong acids dissociate 100% or completely into ions.

Weak acids mostly stay intact and do NOT dissociate 100%.

How do you know if an acid should be labeled as strong or weak? In later lessons, you will examine how the chemical structure of an acid determines its strength.  But for now, you will simply need to memorize a list of the seven most common strong acids.  These are the ones that dissociate 100% in water.  The list is below.

Here is a way to remember the seven strong acids:  Cl-I-Br-ClO-ClO-NO-SO         

In your general chemistry course, if you identify a compound as being an acid but it is not one of the seven listed above, then categorize it as a weak acid.

Writing Ionic & Net Ionic Reactions

An ionic equation shows whether the compounds are dissociated into ions or not.  

 

The steps for creating an ionic equation are simple.

STEP 1     SPLIT UP ANY STRONG ACID INTO ITS IONS
STEP 2     SPLIT UP IONIC COMPOUNDS THAT ARE AQUEOUS (aq)
STEP 3     LEAVE EVERYTHING ELSE ALONE!

An example of this process is shown below for a precipitation reaction.

Example One  

 

Write the full ionic and net ionic equations for the reaction shown below.

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HCl (aq) + NaOH (aq) → NaCl (aq) + H₂O(l)

Answer

Ionic Equation:

H⁺(aq) + Cl⁻(aq) + Na⁺(aq) + OH⁻ (aq) → Na⁺(aq) + Cl⁻ (aq) + H₂O(l)

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Net Ionic Equation:

H⁺(aq) + OH⁻ (aq) →  H₂O(l)

Video & Written Solutions

List of Strong Acids

HCl

HI

HBr

HClO₄

HClO₃

HNO₃

H₂SO₄

Example Two

 

Write the full ionic and net ionic equations for the reaction shown below.

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HF (aq) + NaOH (aq) → NaF (aq) + H₂O(l)

Answer

Ionic Equation:

HF (aq) + Na⁺(aq) + OH⁻ (aq) → Na⁺(aq) + F⁻ (aq) + H₂O(l)

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Net Ionic Equation:

HF (aq) + OH⁻ (aq) → F⁻ (aq) + H₂O(l)

Video & Written Solutions

List of Strong Acids

HCl

HI

HBr

HClO₄

HClO₃

HNO₃

H₂SO₄

Example Three

 

Write the full ionic and net ionic equations for the reaction shown below.

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NaHCO₃ (s) + HC₂H₃O₂ (aq) → NaC₂H₃O₂ (aq) + CO₂ (g) + H₂O(l)

Answer

Ionic Equation:

NaHCO₃(s) + HC₂H₃O₂ (aq) → Na⁺ + C₂H₃O₂⁻ (aq) + CO₂ (g) + H₂O(l)

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Net Ionic Equation:

NaHCO₃(s) + HC₂H₃O₂ (aq) → Na⁺ + C₂H₃O₂⁻ (aq) + CO₂ (g) + H₂O(l)

Video & Written Solutions

List of Strong Acids

HCl

HI

HBr

HClO₄

HClO₃

HNO₃

H₂SO₄

Example Four

 

Write the full ionic and net ionic equations for the reaction shown below.

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Cu (s) + 2 AgNO₃ (aq) → 2 Ag (s) + Cu(NO₃)₂ (aq)

Answer

Ionic Equation:

Cu (s) + 2 Ag⁺ (aq) + 2 NO₃⁻ (aq) → 2 Ag (s) + Cu²⁺ (aq) + 2 NO₃⁻  (aq)

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Net Ionic Equation:

Cu (s) + 2 Ag⁺ (aq) → 2 Ag (s) + Cu²⁺ (aq)

Video & Written Solutions

List of Strong Acids

HCl

HI

HBr

HClO₄

HClO₃

HNO₃

H₂SO₄

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Explore the Intro lessons in each unit​

  • Formula Weights & Mass Percentages

  • Lewis Sructures

  • Ionic Compounds & Lattice Energy

  • Introduction to Kinetics

  • The Concept of Equilibrium

  • Acid-Base Properties

  • The Common Ion Effect

  • Solubility and Solubility Product

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