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Wize University Chemistry Textbook > Chemical Reactions

Net Ionic Equations

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Three Ways to Write Out Chemical Reactions

There are 3 different ways to write out a chemical reaction.

1) Molecular Reaction

This is the way we are most familiar with!

H2​SO4​(aq) + 2NaOH(aq) → 2H2​O(l) + Na2​SO4​(aq)

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2) Complete Ionic Equation

To write the complete ionic equation, we need to look at the molecular reaction and identify which of the molecules can dissociate into ions. Then write out the equation with all of the ions.

Wize Tip
Things that won't dissociate include: solids, liquids, gases, weak acids, weak bases, and combinations of ions that we said are insoluble (from the solubility chart)

Things that will dissociate include: strong acids, strong bases, and combinations of ions that we said are soluble (from the solubility chart)



Next, since we figured out all the molecules that dissociate and balanced the equations, we just put all the ions into the equation so they replace the aqueous molecules:

2H+(aq) + SO42-(aq) + 2Na+(aq) + 2OH-(aq) → 2H2O(l) + 2Na+(aq) + SO42-(aq)

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3) Net Ionic Equation:

For this equation, we just take the complete ionic equation and cross anything out that appears in equal quantities on both sides so that we are left with the net equation.

Complete Ionic Equation:
2H+(aq) + SO42-(aq) + 2Na+(aq) + 2OH-(aq) → 2H2O(l) + 2Na+(aq) + SO42-(aq)





2H+(aq) + 2OH-(aq) --> 2H2O(l)

and this can be further simplified to get the net ionic equation:
H+(aq) + OH-(aq) --> H2O(l)


Wize Tip
When we talk about ionic equations, you may see the term spectator ions used. Spectator ions are the ions that remain unchanged on both sides of the reaction. In this case, the spectator ions are SO42- and Na+.


checklist
Mark Yourself Question
  1. Grab a piece of paper and try this problem yourself.
  2. When you're done, check the "I have answered this question" box below.
  3. View the solution and report whether you got it right or wrong.

Practice: Three Ways to Write Chemical Reactions

Write the molecular, complete ionic and the net ionic equations for the following reaction:

Pb(NO3)2 (aq) + Na2SO4 (aq) → PbSO4 (s) + 2NaNO3 (aq)


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Relating Net Ionic Equations to Ionization of Acids and Bases

Part 1

HCl(aq) +NaOH(aq) →NaCl(aq) + H2O(l)HCl_{\left(aq\right)}\ +NaOH_{\left(aq\right)}\ \rightarrow NaCl_{\left(aq\right)}\ +\ H_2O_{\left(l\right)}

This is a molecular reaction between a (strong/weak)
strong
acid and a (strong/weak)
strong
base.

Review: What type of reaction is this?
Neutralization reaction


If we were asked for the Net Ionic Equation (NIE), then we would need to see which species in the reaction can fully dissociate into ions.

Will HCl(aq) fully dissociate?
Yes because strong acids fully dissociate.

Will NaOH(aq) fully dissociate?
Yes because strong bases fully dissociate.

Will NaCl(aq) fully dissociate?
Yes because it is a compound that has a group 1 ion in it (Na+), which makes it soluble and it will fully dissociate.

Will H2O(l) fully dissociate?
No because liquids do not dissociate.

Now we can write out the Complete Ionic Equation:

H+(aq)+Cl−(aq)+Na+(aq)+OH−(aq)→Na+(aq)+Cl−(aq)+H2O(l)H^+(aq)+Cl^-(aq)+Na^+(aq)+OH^-(aq)\rightarrow Na^+(aq)+Cl^-(aq)+H_2O(l)

Finally, we just cross out anything that appears in equal amounts on both sides to get NIE:


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Part 2


Now what about if we were asked to write the NIE for this reaction between a
Weak
Acid and
Strong
Base:

Review: What type of reaction is this?
Neutralization reaction

Will KOH fully dissociate?
Yes
Will HNO2 fully dissociate?
No
Will KNO2 fully dissociate?
Yes
Will H2O(l) fully dissociate?
No

So let's write out our Complete Ionic Equation:
(only change the species that can fully dissociate into ions, leave things that cannot fully dissociate as they are!)

Now just cross out what appears on both sides to get the NIE:



Extra Practice
Writing Molecular and Net Ionic Equations
Write the balanced net ionic equations (NIE) and molecular equations (ME) for the following. Show all your work. Be sure to show the states in the final equations as well as the charges on any ions.
A. NaCl (aq) + Pb(NO3)2 (aq) →
ME:
Consider the following unbalanced equation:
Zn (s) + NO3− (aq) + H+ (aq) → Zn2+ (aq) + NH4+ (aq) + H2O (l)
Write the net ionic and complete molecular reaction
Net Ionic Equations
Write the balanced net ionic equation (NIE) and molecular equation (ME) for the following. Show all your work. Be sure to show the states in the final equations as well as the charges on any ions.
(NH4)3PO4(aq) + Zn(NO3)2(aq) →
Consider the following unbalanced equation:
Zn (s) + NO3− (aq) + H+ (aq) → Zn2+ (aq) + NH4+ (aq) + H2O (l)
Write the net ionic and complete molecular reaction
Net Ionic and Complete Molecular Equation
Consider the following unbalanced reaction:
KMnO4 (aq) + FeSO4 (aq) + H2SO4 (aq) → Fe2(SO4)3 (aq) + MnSO4 (aq) + K2SO4 (aq) + H2O (l)
Write the balanced net ionic and complete molecular equation
Acid Base Reaction
Consider the following acid base reaction: H3PO4 (aq) + 3NaOH (aq) → Na3PO4 (aq) + 3H2O (l)
Write the complete and net ionic equation.
Predicting Net Ionic Equation
Write the molecular, complete ionic and the net ionic equations for the following reactions, if a reaction occurs.
1. Pb(NO3)2 (aq) + Na2SO4 (aq) →
2. NaCl (aq) + (NH4)2CO3 (aq) →
Chemical reactions: Spectator ions
(a) Write the net ionic equation for the reaction that occurs when aqueous solutions of Na2S and Cu(NO3)2 are mixed.
(b) What are the spectator ions in this reaction?
Periodic Trends: Reactions with Water
When lithium reacts with water the product(s) is(are):
Predicting Net Ionic Equation
Write the molecular, complete ionic and the net ionic equations for the following reaction:
1. Pb(NO3)2 (aq) + Na2SO4 (aq) → PbSO4 (s) + 2NaNO3 (aq)
What is the net ionic equation for the following chemical reaction?
2 Na3PO4 (aq) + 3 CaCl2 (aq) --> 6 NaCl (aq) + Ca3(PO4)2 (s)