Transcript Reactions in Aqueous Solutions

9.1 Net Ionic Equations and
Qualitative Analysis
Learning Goals …
… write an ionic and net ionic equation
… use qualitative analysis (flame test, solution colour
and solubility) to identify ions in a solution
Let’s take a closer look at the reaction between
NaCl (aq) + AgNO3 (aq) 
NaNO3 (aq) + AgCl (s)
What actually happened?
Cl- (aq) + Ag+ (aq)  AgCl (s)
SPECTATOR
IONS
The Na+ and NO3- are still in the solution
A chemical equation written without the spectator ions is
called a net ionic equation. A net ionic equation includes
only those ions or compounds that undergo chemical
change.
TYPES OF EQUATIONS
i.
Balanced Chemical equation
ii.
Ionic equation
iii.
Net ionic equation
Zinc
+
chloride
sodium

phosphate
i.3ZnCl2 (aq) + 2 Na3PO4(aq) 
zinc
+
phosphate
sodium
chloride
Zn3(PO4)2 (s) + 6 NaCl(aq)
ii. 3Zn+2(aq) + 6Cl-(aq) + 6Na+(aq) + 2PO4-3(aq)  Zn3(PO4)2(s) +
6Na+(aq) + 6Cl-(aq)
iii.
3Zn+2(aq) + 2PO4-3(aq) Zn3(PO4)2(s)
Spectator ions: Na+ and Cl-
Now you try one …
Lead (II) + sodium
nitrate
sulfide
i.
Pb(NO3)2 (aq) +

Lead (II)
sulfide
+ sodium
nitrate
Na2S(aq)  PbS(s) + 2 NaNO3(aq)
ii. Pb+2(aq) + 2 NO3-(aq) + 2Na+(aq) + S-2(aq) 
PbS (s) +
2Na+(aq) + 2NO3-(aq)
iii. Pb+2(aq) + S-2(aq) PbS(s)
Spectator ions:
Na+ and NO3-
Qualitative Analysis
• Qualitative Analysis identifies a substance in a sample by
observation of physical and chemical properties.
• You can often identify whether a cation ion is in a sample
by observing one or more of the following:
• Flame Test results
• solution colour
• precipitates formed with select aqueous solutions.
• Qualitative analysis can tell you what ions are present in a
solution.
1. Flame Test
Uses the colour that a sample produces in a flame to
identify the metal ion in the sample
Flame Colours of Some Metals
Ion
Li+
Na+
K+
Cs+
Ca2+
Sr2+
Cu2+
Pb2+
Colour
Crimson Red
Yellow-orange
Purple
Blue
Red-orange
Bright red
Bluish-green
Bluish-white
Fast forward video file to 25 seconds in…
2. Colours of Ions in Solution
Uses the colour of a solution to identify the metal ion
in the sample
Ion
Cr2+
Cu2+
Cr3+
Cu+
Fe2+
Ni2+
Fe3+
Co2+
Mn2+
Pb2+
Colour
blue
green
Pale yellow
Pink
Bluish-white
3. Precipitate Formation
Uses the solubility properties of ions to identify an unknown
ion. We can add a known reactant to a solution and observe
whether a precipitate forms.
Let’s say we wanted to precipitate Pb2+ out of a water
sample…
Let’s look at our Solubility Table …
Lead (II) ions can be precipitated with sulfate ions to yield
solid lead (II) sulfate.
Pb2+ + SO42-  PbSO4 (s)
We can filter off the precipitate and separate it out of the
solution.
SO42- could be obtained from a solution of Na2SO4 (we would
need a nonreactive cation)
Ex)
An ion in solution forms a yellow precipitate when
sodium iodide, NaI (aq), is added to the
solution. The precipitate produces a blue-white
colour when it is heated in a flame. What metal
ion might be present in the solution?
According to the Solubility Rules,
iodides are soluble except if it contains Pb2+, Ag+, and
Hg+ and Hg22+. So the ion must be one of these four.
We can then look to the flame test results to narrow the
ion down.
Pb2+ has a blue-white flame so this must be the ion
present.
CAN I …
… write an ionic and net ionic equation
… use qualitative analysis (flame test and solubility) to
identify ions in a solution
HOMEWORK
p410 #5-10
p414 #12-14
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Flame Colours of Some Metals
Ion
Li+
Na+
K+
Cs+
Ca2+
Sr2+
Cu2+
Pb2+
Colour
Crimson Red
Yellow-orange
Purple
Blue
Red-orange
Bright red
Bluish-green
Bluish-white
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