What this calculator does
A net ionic equation strips a chemical reaction down to only the ions that actually change. Pick two soluble ionic compounds, and this calculator swaps their anions, balances the resulting equation, applies the standard solubility rules to work out which product (if any) precipitates out, then cancels the spectator ions, the ones that stay dissolved and unchanged on both sides, to leave the net ionic equation.
The usual first step is the complete ionic equation, which writes every soluble compound as its separate ions in solution, while any solid stays written as a compound. The net ionic equation is what is left once the spectator ions, the ones doing nothing but sitting in solution before and after, are removed from that complete ionic equation.
The formula
The two reactant cations swap anion partners, and each new compound’s formula is found by cross-balancing the charges, the same method used for any ionic compound. The resulting equation is balanced by finding the smallest whole-number coefficients that conserve every ion. Each product is then checked against the standard solubility rules: if exactly one product is insoluble, it precipitates out and the ions that formed it are the ones kept in the net ionic equation, while the ions left fully dissolved on both sides are the spectator ions and are removed.
| Term | Meaning |
|---|---|
| Complete ionic equation | The reaction written with every soluble compound split into its dissolved ions, and every insoluble compound left as a solid formula. |
| Spectator ion | An ion that appears unchanged, still dissolved, on both sides of the equation, and takes no real part in the reaction. |
| Precipitate | The insoluble solid that forms and drops out of solution when two of the ions present combine. |
The inputs explained
| Field | What to enter |
|---|---|
| Reactant 1 cation | The positive ion in the first reactant compound. |
| Reactant 1 anion | The negative ion paired with it in the first reactant compound. The pairing must already be soluble, since it needs to be dissolved to react. |
| Reactant 2 cation | The positive ion in the second reactant compound. |
| Reactant 2 anion | The negative ion paired with it in the second reactant compound, also assumed soluble. |
When to use it
Identifying a precipitation reaction
Mixing two clear solutions and getting a cloudy precipitate is a double-displacement reaction; the net ionic equation shows exactly which two ions combined to form the solid that came out.
Working through a chemistry problem set
Net ionic equation questions ask for the complete equation, the ionic equation, and the net ionic equation as separate steps; this calculator produces all three so each stage can be checked.
Predicting whether mixing two solutions does anything at all
Not every pairing of soluble compounds produces a reaction. When both possible products are also soluble, nothing precipitates and there is no net ionic equation to write, which is itself a useful thing to confirm.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
Which anion partners with silver to form a precipitate?
Silver nitrate as one reactant, paired against sodium salts of different anions, shows which combinations precipitate and which stay dissolved.
| Anion paired with sodium | Precipitate formed | Net ionic equation |
|---|---|---|
| Chloride | AgCl (Silver chloride) | Ag+ + Cl- -> AgCl(s) |
| Bromide | AgBr (Silver bromide) | Ag+ + Br- -> AgBr(s) |
| Iodide | AgI (Silver iodide) | Ag+ + I- -> AgI(s) |
| Sulfate | Ag2SO4 (Silver sulfate) | 2 Ag+ + SO4^2- -> Ag2SO4(s) |
| Carbonate | Ag2CO3 (Silver carbonate) | 2 Ag+ + CO3^2- -> Ag2CO3(s) |
| Acetate | None; both possible products are soluble | No reaction: every ion stays dissolved, so there is no net ionic equation to write |
Does the spectator cation change the net ionic equation?
The same silver-plus-chloride precipitation reaction, run against chloride salts of three different spectator cations.
| Spectator cation (reactant 2) | Net ionic equation | Spectator ions |
|---|---|---|
| Sodium | Ag+ + Cl- -> AgCl(s) | Sodium (Na+) and Nitrate (NO3-) |
| Potassium | Ag+ + Cl- -> AgCl(s) | Potassium (K+) and Nitrate (NO3-) |
| Ammonium | Ag+ + Cl- -> AgCl(s) | Ammonium (NH4+) and Nitrate (NO3-) |
Questions
What is a net ionic equation?
It is a chemical equation showing only the ions that actually combine to form a new product, usually a precipitate, with the spectator ions, the ones that stay dissolved and unchanged throughout, left out entirely.
What is a spectator ion?
An ion that is present in solution before and after the reaction, in exactly the same dissolved form, without taking part in forming the precipitate. It balances charge in the full equation but contributes nothing to the actual chemical change.
Why do some pairs of soluble compounds produce no net ionic equation?
A reaction only has a net ionic equation if a precipitate, gas or other genuine change occurs. If swapping the anions between two soluble compounds produces two more soluble compounds, nothing has actually changed chemically, even though the ions are technically mixed together, so there is nothing to write beyond noting that no reaction occurs.
How is this different from just balancing the full molecular equation?
The full molecular equation is accurate but includes ions that never really do anything. The net ionic equation is the same reaction with that extra detail stripped away, leaving only the two ions that actually combine, which is usually what a chemistry problem is really asking for.
To check the solubility of a specific ion pairing on its own, use the solubility rules calculator. To work out the correct formula of either the reactant or product compounds by charge alone, see the ionic compound formula calculator.