Description of experiment
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Needed compounds:
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sulphuric acid : H2SO4
ferrous ammonium sulfate hexa hydrate : Fe (NH4)2 (SO4)2 . 6H2O
ferric ammonium sulfate hydrate : Fe NH4 (SO4)2 . 12H2O
cobalt sulfate : CoSO4.7H2O
copper sulfate penta hydrate : CuSO4 . 5H2O
sodium cyanide : NaCN
sodium cyanate : NaOCN
Class:
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elem=C,N,Fe,Co,Cu
coordination
Summary:
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Cyanate ion forms complexes with many metal ions. These complexes have a strong
color and are not stable in acidic solution.
Description:
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Prepare a solution of sodium cyanate in water. Put this aside for further
experiments. This is called solution A.
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Experiment 1: Mix an excess amount of solution A with a light blue solution of
copper sulfate: A deep blue/cyan solution is obtained. The color of the
solution differs quite a lot from the royal blue, obtain from copper(II) ions
and ammonia. It has a fairly strong green hue.
Add a few drops of 20% sulphuric acid: The color changes to light blue and a
lot of bubbles of carbon dioxide are produced.
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Experiment 2: Mix an excess amount of solution A with a pink solution of cobalt
sulfate: A dark blue solution is obtained, much like the solution which is
obtained when a cobalt(II) salt is added to concentrated hydrochloric acid. The
color is slightly more blue.
Add a few drops of 20% sulphuric acid: The deep blue color disappears at once
and the liquid becomes pale pink. Bubbles of carbon dioxide are produced.
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Experiment 3: Mix an excess amount of solution A with a light brown solution of
ferric ammonium sulfate: A yellow solution is obtained, much like a solution of
potassium chromate. After a few minutes of standing the color has changed
somewhat from yellow to golden yellow.
Add a small amount of a solution of ferrous ammonium sulfate: No visible
changes occur.
Add a few drops of 20% sulphuric acid: The color of the solution changes from
deep golden yellow to a pale yellow/green color. Bubbles of carbon dioxide are
produced as well.
Add a few granules of sodium cyanide: More bubbles of gas are produced and the
liquid becomes dark blue (formation of prussian blue).