Unit 3: Chemical Equations and
Stoichiometry
Net Ionic Equations
Net Ionic Equations
• For reactions taking place in water many
substances dissociate (break apart) into ions
• Spectator ions: ions that do not actually
participate in the reaction
• To write a net ionic equation you must
determine what compounds dissociate and which
do not
Net Ionic Rules
Which molecules dissociate???
• Rule 1 – Solids, liquids, and gases
– Do NOT dissociate (break apart)
• Rule 2 – Acids:
– Strong acids dissociate (break apart): HCl, HBr, HI, H2SO4,
HNO3, & HClO4
– Weak acids stay together
• Rule 3 – Bases:
– Strong bases dissociate (break apart): Group 1 and 2
hydroxides (but NOT beryllium hydroxide): LiOH, NaOH,
KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2
– Weak bases stay together
Net Ionic Rules
Which molecules dissociate???
• Rule 4 – Ionic Compounds:
– If soluble: dissociate
– If insoluble: stay together
**Use the table on p. 125 in your textbook or the chart
on your periodic table
Net Ionic Practice
•
Determine whether the following compounds dissociate in
water or not:
1.
2.
3.
4.
5.
H2SO4
FeS
KOH
Ca(NO3)2
Cu3(PO4)2
Steps to Writing Net Ionic Equations
Example: Hydrochloric acid solution and sodium hydroxide
solution yield water and dissolved sodium chloride
Step 1 – Write and balance the molecular form:
HCl (aq) + NaOH (aq)  H2O (l) + NaCl (aq)
Step 2 – Determine which molecules dissociate and rewrite in
ionic form:
H+(aq) + Cl-(aq) + Na+(aq) + OH-(aq)  H2O(l) + Cl-(aq) + Na+(aq)
Spectator ions
Step 3 – Cancel ions that appear on both sides:
H+ (aq) + OH- (aq)  H2O (l)
Net Ionic Example – WS #1
Sodium metal + water  sodium hydroxide + hydrogen gas
Net Ionic Decision Making Tree
Compound
Written in molecular form
Salt
(ionic compound
that is not an acid,
base, or oxide)
Acid (HX)
Base (XOH)
Where X is a negative ion
Where X is a positive ion
Solid, liquid,
gas, oxide
Use Solubility
Rules
Strong = break apart
Weak = keep together
Strong = break apart
Weak = keep together
Keep together
Soluble = aqueous (break apart)
Insoluble = solid (keep together)