Precipitation Reactions
Experiment 7
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Lab #7 Precipitation Reactions
Goals of the Lab
 Learn
about Precipitation Reactions
 Understand ions in a solution
 Identify new compounds formed in a
reaction
 Write equations for reactions
 Complete
 Net
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Ionic
Lab #7 Precipitation Reactions
Aqueous solutions: Ions dissolved in water

Barium Nitrate

Ba(NO3)2
3

Ba2+ + 2 NO3-
Sodium Sulfate
Na2SO4

Lab #7 Precipitation Reactions
2Na+ + SO42-
Add the 2 aqueous solutions together:
 The
ions are able to intermingle
 There may be an attraction, that results in a
reaction (energetically favorable)
 Possible Reactions include
Formation of a gas
 Formation of water

 Formation
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of a Precipitate (ppt.)
Lab #7 Precipitation Reactions
How do I know what formed??
In reaction A you started with Barium Nitrate and
Sodium Sulfate
There is a reaction as evidenced by the white
precipitate
 What is it?
Barium Sulfate OR Sodium Nitrate?

You must do some detective work
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Lab #7 Precipitation Reactions
Barium Sulfate OR Sodium Nitrate?

Is there any place else that
BaSO4 could have formed?

Is there any place else
where NaNO3 could have
formed?
YES
Yes
In Reaction B
In Reaction G
What happened in each reaction?
If an ion pair forms a ppt. in one reaction, assume they will get
together any chance they get!
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Lab #7 Precipitation Reactions
The ‘intermingling’ has caused a
Other ‘non-reacting’ ions remain
reaction
soluble…. Still in solution

The barium ions and
the sulfate ions have an
attraction to each other,
they form a solid
compound and “fall”
out of solution as a
precipitate
Lab #7 Precipitation
Reactions
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Data Analysis
Reaction
A
Solution Pairs
Yielding
Precipitates
Formulas of
Possible
Precipitates
Reasons for Choice of
Precipitate
Ba(NO3)2
NaNO3
Na2SO4
BaSO4
In rxn B, Ba2+ and
SO42- formed a ppt.
when mixed.
In rxn G, Na+ and NO3were both present with
no ppt. formed.
B
Lab #7 Precipitation
Reactions
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Complete and
Net Ionic Equations
Lab #7 Precipitation
Reactions
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Lab #7 Precipitation Reactions
Sometimes parts of the equation do nothing
but sit and watch.
Spectators
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Lab #7 Precipitation Reactions
Complete ionic vs. net ionic
Sodium sulfate + Barium Chloride react to form Solid barium sulfate
and Sodium chloride
2 Na+ (aq) + SO42- (aq) + Ba2+ (aq) + 2 Cl- (aq) 
BaSO4 (s) + 2 Na+ (aq) + 2 Cl- (aq)
NaCl is a strong electrolyte, so it does not combine to form a solid
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Lab #7 Precipitation Reactions