Net Ionic Equations
Introduced| English |
|---|
| net ionic equation/net aɪˈɒnɪk ɪˈkweɪʒn/ |
| spectator ions/spekˈteɪtə ˈaɪɒnz/ |
Cutting a reaction to its core
- Mix two clear solutions and a solid suddenly appears.
- But most of the dissolved ions just drift by, unchanged.
- Only a few actually take part in the change.
- We can strip an equation down to just those.
Three ways to write it
- The molecular equation shows whole compounds.
- The complete ionic equation splits every dissolved ionic compound into ions.
- The net ionic equation 净离子方程式 keeps only the ions that react.
Which species is split into ions in the complete ionic equation?
Only dissolved (aqueous) ionic compounds are written as ions.
Spectator ions cancel
- Spectator ions 旁观离子 appear unchanged on both sides.
- Cancel them, just like identical terms in algebra.
- What remains is the net ionic equation.
A spectator ion is one that...
Spectators do not change, so they cancel out.
After cancelling spectator ions, what remains is the ____ ionic equation.
The leftover reacting ions form the net ionic equation.
The real change
- The net ionic equation shows only the species that actually change.
- For a precipitate, it is the two ions that join to form the solid.
- It captures the true chemistry, stripped of clutter.
Write a net ionic equation
Strip a reaction down to the ions that actually react.
A solid precipitate is written as separate ions in the net ionic equation.
Only aqueous ions split; a solid stays as one whole formula.
A correct net ionic equation must balance both atoms and charge.
Both mass and charge are conserved.
$\text{AgNO}_3 + \text{NaCl} \to \text{AgCl} + \text{NaNO}_3$.
- $\text{Na}^+$ and $\text{NO}_3^-$ are spectators, so cancel them.
- Net ionic equation: $\text{Ag}^+ + \text{Cl}^- \to \text{AgCl}$.
For $\text{Ag}^+ + \text{NO}_3^- + \text{Na}^+ + \text{Cl}^- \to \text{AgCl} + \text{Na}^+ + \text{NO}_3^-$, the net ionic equation is...
$\text{Na}^+$ and $\text{NO}_3^-$ are spectators; only Ag and Cl react.
Only aqueous (dissolved) ionic compounds split into ions -- solids, liquids, and gases stay whole. Spectator ions are identical on both sides, so cancel only those. And the net ionic equation must still balance in both atoms and charge.
A net ionic equation strips a reaction to the ions that actually change. Split aqueous ionic compounds into ions, cancel the spectator ions that are identical on both sides, and keep the rest -- like $\text{Ag}^+ + \text{Cl}^- \to \text{AgCl}$. The result must balance atoms and charge.