Complete and Net Ionic Equations

Core Concept

Complete and net ionic equations are used to show the detailed behavior of ions in aqueous reactions. These equations help identify which ions participate directly in the reaction and which remain unchanged.

  • Identify State Symbols: Only substances labeled as aqueous $(aq)$ can be broken into ions; solids $(s)$, liquids $(l)$, and gases $(g)$ must remain as whole molecules.

  • Cross Out Spectators: Physically draw a line through identical ions on both sides of your complete ionic equation to ensure your final net equation is accurate.

  • Distribute Coefficients: When breaking a compound like $2NaCl$ into ions, remember to apply the coefficient to both the cation and the anion ($2Na^+$ and $2Cl^-$).

  • Verify the Solid: The product of your net ionic equation should always be the insoluble precipitate you identified using your solubility rules.

Test Yourself

Assorted Multiple Choice
A constant current is passed through an electrolytic cell for 45.0 minutes, delivering a total charge of 8,100 Coulombs. How many moles of electrons were transferred during this process? (Faraday's constant = 96,485 C/mol e⁻)

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Episode

Complete and Net Ionic Equations

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Converting Molecular to Complete Ionic Equations

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Identification of Spectator Ions

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Net Ionic Equations for Precipitation Reactions

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Acid-Base Neutralization (Strong Acids and Bases)

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Predicting Products and Determining "No Reaction"

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Gas-Forming Reactions

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Assorted Multiple Choice

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Key Definitions

  1. Molecular Equation:

    • The molecular equation shows all the reactants and products in their complete, neutral forms.

    • Example: $\text{NaCl (aq)} + \text{AgNO}_3 \text{(aq)} \rightarrow \text{NaNO}_3 \text{(aq)} + \text{AgCl (s)}$

  2. Complete Ionic Equation:

    • The complete ionic equation shows all the soluble ionic compounds broken down into their individual ions.

    • Insoluble compounds, weak electrolytes, and gases are left in their molecular form.

    • Example: $\text{Na}^+ \text{(aq)} + \text{Cl}^- \text{(aq)} + \text{Ag}^+ \text{(aq)} + \text{NO}_3^- \text{(aq)} \rightarrow \text{Na}^+ \text{(aq)} + \text{NO}_3^- \text{(aq)} + \text{AgCl (s)}$

  3. Net Ionic Equation:

    • The net ionic equation shows only the ions and molecules directly involved in the reaction, excluding spectator ions (ions that appear unchanged on both sides of the equation).

    • Example: $\text{Ag}^+ \text{(aq)} + \text{Cl}^- \text{(aq)} \rightarrow \text{AgCl (s)}$

Steps for Writing Complete and Net Ionic Equations

  1. Write the Balanced Molecular Equation:

    • Start by writing the balanced chemical equation for the reaction, with all compounds in their molecular forms.

  2. Identify Soluble and Insoluble Compounds:

    • Use solubility rules to determine which compounds are soluble (aqueous, or aq) and which are insoluble (solid, or s).

    • Common Solubility Rules:

      • Compound containing Group I ions (i.e., sodium ($Na^+$), potassium ($K^+$)) are soluble.

      • Compounds containing ammonium ($NH_4^+$​) are soluble.

      • All compounds with nitrate ($NO_3^-$​) are soluble.

  3. Write the Complete Ionic Equation:

    • For all soluble ionic compounds, write them as separate ions.

    • For insoluble compounds, weak electrolytes, and gases, write them in their molecular forms.

    • Example: $\text{Na}^+ \text{(aq)} + \text{Cl}^- \text{(aq)} + \text{Ag}^+ \text{(aq)} + \text{NO}_3^- \text{(aq)} \rightarrow \text{Na}^+ \text{(aq)} + \text{NO}_3^- \text{(aq)} + \text{AgCl (s)}$

  4. Identify and Remove Spectator Ions:

    • Spectator ions are ions that appear unchanged on both sides of the equation.

    • Remove the spectator ions from the complete ionic equation to focus on the ions directly involved in the reaction.

  5. Write the Net Ionic Equation:

    • Write the remaining ions and compounds that actually participate in the reaction.

    • Example: $\text{Ag}^+ \text{(aq)} + \text{Cl}^- \text{(aq)} \rightarrow \text{AgCl (s)}$

Quick Checklist for Solving Problems

  1. Write the balanced molecular equation.

  2. Use solubility rules to identify soluble/insoluble species.

  3. Write the complete ionic equation.

  4. Cancel spectator ions.

  5. Write the net ionic equation.

  6. Verify that charges and atoms are balanced.

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