A solid-solid reaction
Demonstration
This is a very quick demonstration showing that two solids can react together. White lead
nitrate and white potassium iodide react to make yellow lead iodide.
Lesson organisation
This demonstration is very quick and will take no more than 2 minutes.
Chemicals
Lead nitrate (TOXIC, DANGEROUS FOR THE ENVIRONMENT), 20g
Potassium iodide, 20g
Refer to Health & Safety and Technical notes section below for additional information.
Apparatus
For one demonstration:
Eye protection
A small screw-top jar
Balance
Weighing boats or similar, 2
Health & Safety and Technical notes
Read our standard health & safety guidance [1]
Wear eye protection and wash hands after the demonstration.
Lead nitrate, Pb(NO3)2(s), (TOXIC, DANGEROUS FOR THE ENVIRONMENT) - see
CLEAPSS Hazcard.
Potassium iodide, KI(s) - see CLEAPSS Hazcard.
1 The resulting solid mixture from the demonstration should be retained in a sealed container for
professional disposal.
Procedure
a Weigh out equal masses of both compounds. These are then in approximately the
stoichiometric ratio. Between 10 g and 20 g of each is suitable.
b Mix the solids in a screw topped jar and shake for several seconds. The yellow colour of lead
iodide will be seen.
c Make a little more of the mixture and place it quickly into a beaker containing a little water. The
reaction will be much more rapid.
Teaching notes
The demonstration might have more impact if the jar is opaque and the yellow product can be
poured out and shown to the unsuspecting audience. Have a white background available.
Point out that for a reaction ot occur, particles of the reactants must meet. This is much easier in
solution (where the particles are free to move) than in the solid state.
The reaction is:
Pb(NO3)2(s) + 2KI(s) → 2KNO3(s) + PbI2(s)
All of these compounds are white except lead iodide, which is yellow.
Lead ethanoate can be substituted for lead nitrate, but the reaction is much slower.
The experiment Diffusion in liquids [2] is a class practical using the same compounds but as
solutions.
Health & Safety checked April 2008
Source URL: http://www.nuffieldfoundation.org/practical-chemistry/solid-solidreaction
Links:
[1] http://www.nuffieldfoundation.org/node/1634/
[2] http://www.nuffieldfoundation.org/node/2907