Ionic Equation Practice Problems- Writing Net Ionic Equations

What Are Ionic Equations?

When chemicals dissolve in water, they break apart into ions. Ionic equations show these species explicitly instead of hiding them as complete compounds. This matters because the actual chemical reaction happens between individual ions, not neutral molecules.

Most students struggle with ionic equations because they don't understand what actually exists in solution. Once you see the ions, writing the equation becomes straightforward.

The Three Types of Equations You Need to Know

Molecular Equation

The molecular equation shows complete formulas as if everything stayed intact. It's useful for describing what you dump into the beaker, but it hides what's really happening.

Example: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)

Complete Ionic Equation

Break apart all soluble compounds into their ions. This is where you see everything floating around in solution.

Example: Ag⁺(aq) + NO₃⁻(aq) + Na⁺(aq) + Cl⁻(aq) → AgCl(s) + Na⁺(aq) + NO₃⁻(aq)

Net Ionic Equation

Remove spectator ions—the ones that don't participate. What's left is the actual reaction.

Example: Ag⁺(aq) + Cl⁻(aq) → AgCl(s)

How to Write Net Ionic Equations: Step by Step

Here's the process. Follow it exactly every time and you'll never mess up.

1. Write the balanced molecular equation first. Get your formulas correct.
2. Identify all soluble compounds using solubility rules. These break into ions.
3. Write the complete ionic equation by splitting everything that dissolves.
4. Identify spectator ions—ions that appear on both sides unchanged.
5. Cancel spectator ions from both sides.
6. Write the net ionic equation with what remains.

Solubility Rules You Must Memorize

You can't do this without knowing what dissolves. Here are the basics:

• All nitrates, acetates, and most alkali metal salts are soluble
• All chlorides, bromides, and iodides are soluble except Ag⁺, Pb²⁺, and Hg₂²⁺
• All sulfates are soluble except Ba²⁺, Pb²⁺, Ca²⁺, and Sr²⁺
• All hydroxides are insoluble except those of alkali metals and Ba²⁺
• All carbonates, phosphates, sulfides, and sulfites are insoluble except those of alkali metals

Practice Problem 1: Precipitation Reaction

Problem: Write the net ionic equation when aqueous solutions of barium chloride and sodium sulfate are mixed.

Step 1 - Molecular equation:

BaCl₂(aq) + Na₂SO₄(aq) → BaSO₄(s) + 2NaCl(aq)

Step 2 - Complete ionic equation:

Ba²⁺(aq) + 2Cl⁻(aq) + 2Na⁺(aq) + SO₄²⁻(aq) → BaSO₄(s) + 2Na⁺(aq) + 2Cl⁻(aq)

Step 3 - Identify spectators: Na⁺ and Cl⁻ appear on both sides

Step 4 - Net ionic equation:

Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)

Practice Problem 2: Acid-Base Neutralization

Problem: Write the net ionic equation for the reaction between hydrochloric acid and sodium hydroxide.

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

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

Net ionic:

H⁺(aq) + OH⁻(aq) → H₂O(l)

This is the universal net ionic equation for any strong acid reacting with any strong base.

Practice Problem 3: Gas Formation

Problem: Write the net ionic equation when sodium carbonate reacts with hydrochloric acid.

Molecular: Na₂CO₃(aq) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + CO₂(g)

Complete ionic: 2Na⁺(aq) + CO₃²⁻(aq) + 2H⁺(aq) + 2Cl⁻(aq) → 2Na⁺(aq) + 2Cl⁻(aq) + H₂O(l) + CO₂(g)

Net ionic:

CO₃²⁻(aq) + 2H⁺(aq) → H₂O(l) + CO₂(g)

Practice Problem 4: Single Replacement

Problem: Write the net ionic equation when zinc metal is placed in copper(II) sulfate solution.

Molecular: Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

Complete ionic: Zn(s) + Cu²⁺(aq) + SO₄²⁻(aq) → Zn²⁺(aq) + SO₄²⁻(aq) + Cu(s)

Net ionic:

Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)

Note that solid metals don't break into ions. They stay as atoms.

Common Mistakes That Will Cost You Points

• Forgetting to balance charges — your ions must add up correctly on both sides
• Breaking apart insoluble compounds — solids and gases don't dissociate
• Forgetting states of matter — (s), (l), (g), (aq) matter and are required
• Including spectator ions — if it appears unchanged on both sides, remove it
• Writing incorrect formulas — if your starting formulas are wrong, nothing else matters

Quick Reference: Comparing Equation Types

Getting Started: Your Working Method

When you sit down to write a net ionic equation, use this checklist:

1. Write the molecular equation and balance it
2. Mark each compound as soluble or insoluble
3. Write the complete ionic form
4. Circle or highlight ions on the left and right
5. Cross out species appearing identically on both sides
6. Write what's left as your net ionic equation
7. Check that charges and atoms balance

Do this every single time. Speed comes with practice, not with skipping steps.

Why Net Ionic Equations Matter

You need this skill for several reasons. In the lab, net ionic equations tell you what precipitate to expect and why. In exams, they're testing whether you understand what actually happens in solution versus what just looks like it's happening.

The net ionic equation isolates the chemistry. It shows you the reaction without the noise. Master this and you'll understand reactions at a level most students never reach.