TEACHING LABORATORY
Chemical Reactions
VIRTUAL CHEMLAB
PERFORMANCE LABORATORY
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Challenge
The MCQ Challenge
ChemQuest
  CHEMICAL REACTIONS
 


Precipitation Reactions

Precipitation Explained

Before mixing
After mixing

Ions in Lead(II) nitrate solution:
Pb2+, NO3-

Ions in potassium iodide solution:
K+, I-
  1. lead(II) ions combine with iodide ions to form lead(II) iodide, which is insoluble.

    Pb2+ + 2I-     ----->    PbI2 (s)

    This is the precipitation reaction.

  2. potassium ions and nitrate ion remain as free, mobile ions in the solution.

    K+ (aq) and NO3- (aq)

    Potassium and nitrate ions are called spectator ions because they do not take part in the precipitation reaction.

Click on the animation to see this precipitation process. You should see the spectator ions moving about randomly during the process.

The only chemical change which occurs is the attraction of the Pb2+ and I- ions to form an insoluble ionic salt, PbI2.

 

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