Net Ionic Equations
Context
• Some things are soluble, some are not
• Ionic compounds dissociate into ions
• Precipitates can be formed if a
combination of ions results in an
insoluble compound
• How do we show this?
Ions in Solution
In aqueous solutions, ionic compounds dissociate into their
ions.
E.g. Sr(NO3)2(aq) → Sr2+(aq) + 2NO3-(aq)
Some combinations of ions result in a precipitate. It is these
ions ONLY that are actually reacting
Total ionic equations show all dissociated ions of soluble
ionic compounds.
Spectator ions are ions that remain in solution (do not form
a precipitate) and therefore are not involved in a chemical
reaction.
Net ionic equations show only ions involved in a chemical
reaction (I.e. spectator ions are NOT included)
An Example
The reaction between aqueous sodium chloride & silver nitrate.
Chemical Equation:
NaCl(aq) + AgNO3(aq)  NaNO3(aq) + AgCl(s)
Total Ionic Equation:
Na+(aq) + Cl-(aq) + Ag+(aq) + NO3-(aq)  Na+(aq) + NO3-(aq) + AgCl(s)
Net ionic Equation:
Ag+(aq) + Cl-(aq)  AgCl(s)
Another Example
The reaction between potassium carbonate & barium nitrate.
Chemical Equation:
K2CO3 (aq) + Ba(NO3)2(aq)  ?
K2CO3 (aq) + Ba(NO3)2(aq)  2 KNO3 (aq) + BaCO3 (s)
Total Ionic Equation:
2 K+(aq) + CO32-(aq) + Ba2+(aq) + 2NO3-(aq)  2 K+(aq) + 2NO3-(aq) + BaCO3(s)
Net ionic Equation: Ba2+ + CO32-  BaCO3(s)
• By predicting if a product will make a
precipitate, you can calculate how much
is produced
• Precipitation reactions can also be used
to test for the presence of certain ions in
an unknown solution
• This is called qualitative analysis
Qualitative Analysis
1. Solution Colour
– The identity of a metal ion can be inferred
by the colour of the aqueous solution it
forms
Ion
Solution Colour
Cu2+
blue
Co2+
pink
Ni2+
green
MnO4
purple
Alkali Metals
colourless
2. Flame Test
– The identity of a metal (atom or ion) can
be inferred by the colour of the flame
containing the metal
Metal
Flame Colour
Li+
red
Na+
yellow
K+
violet
Cu2+
Blue-green
Sr2+
red
http://www.youtube.com/watch?v=1EXr_L7Ojqg
3. Sequential Analysis
– Unknown aqueous ions can be identified
by testing the solubility, by adding ions
known to form low solubility products
– More than one test can be done in
sequence to identify more than one ion
Sequential Analysis
aqueous solution possibly
containing: Ag+, Pb2+, Sr2+ (only
possibilities)
+ NaC2H3O2 (aq)
ppt
contains: Ag+
filter
does not contain
Ag+
ppt
test
filtrate
contains: Pb2+
filter
no ppt
no ppt
ppt
+ NaCl(aq) no ppt
does not contain: Pb2+
ppt
test no ppt
filtrate
ppt
contains: Sr2+
+ Na2CO3(aq)
no ppt
does not contain:
Sr2+
Practice
• worksheet