Net Ionic Equation Example- How to Write It
What the Hell Is a Net Ionic Equation?
Let's cut the crap. A net ionic equation shows exactly what's happening in a chemical reaction — the ions that actually change, stripped of the spectators.
That's it. The stuff that doesn't participate? Gone.
You're expected to write these because it tells you the real chemistry happening. Not the circus. Just the main act.
The Three Types of Equations You Need to Know
Most textbooks throw all three at you. Here's the breakdown so you stop confusing them:
Molecular Equation
This is the full equation with complete formulas. Every compound written as if it were a single unit.
Example: Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(s) + 2KNO₃(aq)
Looks clean. Tells you almost nothing about what's actually moving around in solution.
Complete Ionic Equation
Now you break apart all the soluble compounds into their ions. This is where you see everything.
Example: Pb²⁺(aq) + 2NO₃⁻(aq) + 2K⁺(aq) + 2I⁻(aq) → PbI₂(s) + 2K⁺(aq) + 2NO₃⁻(aq)
See those ions that appear on both sides? Those are spectator ions. They show up, watch the drama, and leave unchanged.
Net Ionic Equation
You remove the spectators. What's left is the actual reaction.
Example: Pb²⁺(aq) + 2I⁻(aq) → PbI₂(s)
This tells you lead ions react with iodide ions to form solid lead iodide. That's the chemistry.
How to Write a Net Ionic Equation: Step by Step
Stop guessing. Here's the actual process:
Step 1: Write the Balanced Molecular Equation
Start here. Get your reactants and products correct. Balance it properly.
Example: AgNO₃(aq) + NaCl(aq) → AgCl(s) + NaNO₃(aq)
Step 2: Split Everything Into Ions
Only split compounds that are aqueous (aq). Solids, liquids, and gases stay intact.
Ag⁺(aq) + NO₃⁻(aq) + Na⁺(aq) + Cl⁻(aq) → AgCl(s) + Na⁺(aq) + NO₃⁻(aq)
Step 3: Identify and Cancel Spectator Ions
Look for ions that appear on both sides unchanged. These are your spectators. Cancel them out.
Na⁺ and NO₃⁻ appear on both sides. Gone.
Step 4: Write What's Left
Whatever remains is your net ionic equation.
Result: Ag⁺(aq) + Cl⁻(aq) → AgCl(s)
That's it. Four steps. No magic.
Common Net Ionic Equation Examples
Here are solid examples with explanations. Study these until you can do them in your sleep.
Example 1: Precipitation Reaction
Reaction: Sodium sulfate + barium chloride
Molecular: Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)
Complete Ionic: 2Na⁺(aq) + SO₄²⁻(aq) + Ba²⁺(aq) + 2Cl⁻(aq) → BaSO₄(s) + 2Na⁺(aq) + 2Cl⁻(aq)
Net Ionic: Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)
Barium sulfate is insoluble. That's what precipitates out.
Example 2: Gas Formation
Reaction: Hydrochloric acid + sodium carbonate
Molecular: 2HCl(aq) + Na₂CO₃(aq) → H₂O(l) + CO₂(g) + 2NaCl(aq)
Complete Ionic: 2H⁺(aq) + 2Cl⁻(aq) + 2Na⁺(aq) + CO₃²⁻(aq) → H₂O(l) + CO₂(g) + 2Na⁺(aq) + 2Cl⁻(aq)
Net Ionic: 2H⁺(aq) + CO₃²⁻(aq) → H₂O(l) + CO₂(g)
Carbonic acid forms briefly, then decomposes into water and CO₂ gas. The net ionic shows this directly.
Example 3: Neutralization Reaction
Reaction: Hydrochloric acid + 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 for any strong acid-strong base neutralization. Memorize it.
Solubility Rules: Your Non-Negotiable Reference
You need to know which compounds are soluble and which aren't. This determines what splits into ions and what stays solid.
| Compound Type | Solubility | Exceptions |
|---|---|---|
| Group 1 ions (Na⁺, K⁺, etc.) | Always soluble | None |
| NH₄⁺ salts | Always soluble | None |
| Nitrates (NO₃⁻) | Always soluble | None |
| Acetates (CH₃COO⁻) | Usually soluble | Ag⁺ salts |
| Chlorides, bromides, iodides | Usually soluble | Ag⁺, Pb²⁺, Hg₂²⁺ |
| Sulfates (SO₄²⁻) | Usually soluble | Ba²⁺, Pb²⁺, Ca²⁺ |
| Carbonates (CO₃²⁻) | Usually insoluble | Group 1, NH₄⁺ |
| Hydroxides (OH⁻) | Usually insoluble | Group 1, Ca²⁺, Ba²⁺, Sr²⁺ |
| Sulfides (S²⁻) | Usually insoluble | Group 1, NH₄⁺, Group 2 |
| Phosphates (PO₄³⁻) | Usually insoluble | Group 1, NH₄⁺ |
Strong vs Weak Electrolytes: Don't Skip This
Weak electrolytes don't fully dissociate. You cannot split them completely into ions like strong electrolytes.
Strong Electrolytes — split completely:
- Strong acids (HCl, HBr, HI, HNO₃, H₂SO₄, HClO₄)
- Strong bases (NaOH, KOH, LiOH, Ba(OH)₂, Ca(OH)₂)
- All soluble ionic compounds
Weak Electrolytes — do NOT split completely:
- Weak acids (CH₃COOH, HF, H₂CO₃)
- Weak bases (NH₃, amines)
- Insoluble compounds
- Water
If you split a weak electrolyte completely, your net ionic equation will be wrong. Period.
Practice Problems to Test Yourself
Try these before checking the answers. No peeking.
Problem 1
Write the net ionic equation for: FeCl₃(aq) + NaOH(aq) →
Hint: Iron(III) hydroxide is insoluble.
Answer: Fe³⁺(aq) + 3OH⁻(aq) → Fe(OH)₃(s)
Problem 2
Write the net ionic equation for: HCl(aq) + Ca(OH)₂(aq) →
Answer: 2H⁺(aq) + Ca(OH)₂(s) → Ca²⁺(aq) + 2H₂O(l)
Wait — that's not fully simplified. Let's redo it properly:
Complete ionic: 2H⁺(aq) + 2Cl⁻(aq) + Ca²⁺(aq) + 2OH⁻(aq) → Ca²⁺(aq) + 2Cl⁻(aq) + 2H₂O(l)
Net ionic: H⁺(aq) + OH⁻(aq) → H₂O(l)
Problem 3
Write the net ionic equation for: K₂SO₄(aq) + Ba(NO₃)₂(aq) →
Answer: Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s)
Common Mistakes That Will Cost You Points
These errors show up constantly. Stop making them.
- Splitting insoluble compounds: AgCl(s) stays as AgCl(s). You don't write Ag⁺ + Cl⁻.
- Forgetting to balance: Charges must balance. If your equation has a +3 charge on one side and +2 on the other, it's wrong.
- Including weak electrolytes as ions: Acetic acid doesn't fully dissociate. Write it as CH₃COOH, not CH₃COO⁻ + H⁺.
- Not canceling properly: Check that you're canceling the same ion in the same state. NO₃⁻(aq) cancels NO₃⁻(aq), not NO₃⁻(solid).
- Writing state symbols wrong: (aq) for dissolved, (s) for precipitate, (g) for gas, (l) for liquid. These matter.
Quick Reference: Common Net Ionic Equations
| Reaction Type | Net Ionic Equation |
|---|---|
| Any strong acid + strong base | H⁺ + OH⁻ → H₂O |
| Any soluble silver salt + halide | Ag⁺ + X⁻ → AgX(s) |
| Barium salt + sulfate | Ba²⁺ + SO₄²⁻ → BaSO₄(s) |
| Carbonate + strong acid | CO₃²⁻ + 2H⁺ → H₂O + CO₂(g) |
| Ammonia + strong acid | NH₃ + H⁺ → NH₄⁺ |
| Metal + acid | Metal + 2H⁺ → Metal²⁺ + H₂(g) |
Final Word
Net ionic equations aren't complicated. They're tedious. There's a difference.
Learn your solubility rules. Learn which compounds are strong electrolytes. Follow the four steps. Check your work.
That's the entire process. No shortcuts. No tricks. Just practice until you can do it without thinking.