Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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ammonia : NH3
periodic acid : H5IO6
iodic acid : HIO3
Class:
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elem=N,I
precipitation
redox
Summary:
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Ammonium iodate can very easily be prepared by adding a slight excess of
ammonia to a solution of iodic acid in water. The dry compound is stable, but
when it is heated, it violently decomposes, but it does not explode.
Ammonium periode can be prepared in a similar way. When ammonium periodate is
heated, then it explodes, giving a cloud of iodine.
Description:
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Dissolve some iodic acid in water: A colorless solution is obtained.
Carefully add some 12% ammonia: The ammonia does not completely mix, the
ammonia remains in the upper part of the liquid. A vague boundary layer is
formed, and crystals of solid ammonium iodate are formed in this layer (which
has a thickness of approximately 1.5 mm).
Swirl the test tube, such that the liquids completely mix: A compact
crystalline white precipitate is formed, which quickly settles at the bottom.
The colorless liquid above this precipitate easily can be decanted.
Put the wet precipitate (which has a smell of ammonia, some excess ammonia was
used) in a petri dish and put the petri dish in a warm dry place (radiator, 50
C): After a few hours a dry white solid is obtained, which easily can be
scraped off the glass and which is nicely dry. The solid is not hygroscopic at
all.
Put a SMALL amount (just a few tens of mg) of this white solid in a dry test
tube and carefully heat above a flame: Nothing seems to happen, but at a
certain moment there is a sudden strong hissing noise and the solid is gone. A
cloud of grey iodine is formed and the glass is covered with crystals of iodine
at the cooler parts.
The solid very quickly decomposes. It is not an explosion, but the
decomposition is very fast.
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Dissolve some periodic acid in water: A colorless solution is obtained.
Carefully add some 12% ammonia: The ammonia does not completely mix, the
ammonia remains in the upper part of the liquid. In the boundary layer, very
fine crystals of ammonium periodate are formed. These crystals are smaller than
the crystals, formed in the reaction with iodic acid.
Swirl the test tube, such that the liquids completely mix: A compact
powder-like white precipitate is formed, which fairly quickly settles at the
bottom. The colorless liquid above this precipitate easily can be decanted.
Put the wet precipitate (which has a smell of ammonia, some excess ammonia was
used) in a petri dish and put the petri dish in a warm dry place (radiator, 50
C): After a few hours a dry white solid is obtained, which easily can be
scraped off the glass and which is nicely dry. The solid is not hygroscopic at
all. This solid is a very fine powder, which has a finer structure than the
solid, obtained with iodic acid.
Put a SMALL amount (just a few tens of mg) of this white solid in a dry test
tube and carefully heat above a flame: Nothing seems to happen, but at a
certain moment there is a violent explosion, which might crack the test tube! A
cloud of purple iodine vapor is formed and the glass is covered with crystals
of iodine at the cooler parts.