CHE 121
Writing Net Ionic Equations
1. Decide the type of reaction.
2. Predict the products.
3. Write the balanced molecular equation.
Rev. FA2015
4. Write the ionic equation
5. Eliminate spectator ions
6. Write the net ionic equation.
Example: Calcium hydroxide and hydrocyanic acid (HCN) solutions are mixed.
1. Calcium hydroxide is a base. HCN is an acid, so this is a neutralization reaction.
2. A neutralization reaction produces a salt plus water (usually). Acid + Base " Salt + Water
Writing the balanced equation starts with writing correct formulas. Calcium hydroxide is a base, but also an ionic
compound. The ion formed by calcium is Ca2+ (from the periodic table) and hydroxide is OH-. The formula is Ca(OH)2.
The salt formed will be the cation from the base (Ca2+) with the anion from the acid (CN-)
Ca(OH)2 (aq) + 2 HCN (aq) " Ca(CN)2 (aq) + 2 H2O (l)
3. To write net ionic equations you must be able to identify strong electrolytes.
a. Strong electrolytes are written as dissociated ions. Strong electrolytes are: soluble ionic compounds, strong
acids, strong bases. (Memorize the list of strong acids!)
Ca(OH)2 is a strong base (also a somewhat soluble ionic salt) and therefore a strong electrolyte. Write the
ions and numbers of ions in the compound: Ca2+ (aq) + 2 OH- (aq)
Ca(CN)2 is a soluble ionic compound and therefore a strong electrolyte. Write the ions and numbers of ions
in the compound: Ca2+ (aq) + 2 CN- (aq)
b. Molecular formulas are written for weak electrolytes and non-electrolytes.
i. Weak electrolytes are: weak acids and weak bases (i.e. ammonia, amines, any acid not on the strong
acid list).
HCN is a weak electrolyte because it is a weak acid. It is written exactly as it appeared in
the molecular equation: 2 HCN (aq)
ii. Non-electrolytes are covalent compounds that do not dissociate in water (i.e. ethanol or glucose).
H2O is a non-electrolyte because it is a covalent compound. (Due to autoionization it
could also be considered a weak electrolyte, but there is very little dissociation.) It is
written exactly as it appeared in the molecular equation: 2 H2O
4. Write the ionic equation:
Ca2+ (aq) + 2 OH- (aq) + 2 HCN (aq) " Ca2+ (aq) + 2 CN- (aq) + 2 H2O (l)
5. Spectator ions are the ions that appear on both sides of the equation: Ca2+ is the only spectator ion in this equation.
Ca2+ (aq) + 2 OH- (aq) + 2 HCN (aq) " Ca2+ (aq) + 2 CN- (aq) + 2 H2O (l)
6. Write the net ionic equation (NIE): 2 OH- (aq) + 2 HCN (aq) " 2 CN- (aq) + 2 H2O (l) can be simplified to
OH- (aq) + HCN (aq) " CN- (aq) + H2O (l)
Write the molecular and net ionic equations.
1. Solid aluminum is placed in a solution of copper (II) chloride. Type of reaction? ___________________________
Molecular equation:
Strong electrolytes? _________________________
Ionic Equation:
Spectator ions? ____________________________
NIE:
2. Solutions of sodium carbonate and calcium nitrate
are mixed.
Molecular equation:
Type of reaction? ____________________________
Strong electrolytes? _________________________
Ionic Equation:
Spectator ions? ____________________________
NIE:
3. Solid copper is placed in a solution of hydrobromic acid.
Molecular equation:
Type of reaction? ____________________________
Strong electrolytes? _________________________
Ionic Equation:
Spectator ions? ____________________________
NIE: