Description of experiment
Below follows a plain text transcript of the selected experiment.
Needed compounds:
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copper sulfate penta hydrate : CuSO4 . 5H2O
cobalt sulfate : CoSO4.7H2O
nickel sulfate : NiSO4 . 6H2O
chrome alum : KCr(SO4)2 . 12H2O
vanadyl sulfate : VOSO4.5H2O
sulphuric acid : H2SO4
Class:
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elem=S,V,Cr,Co,Ni,Cu
coordination
Summary:
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When hydrated sulfate-salts are heated, which only loose water, then their
properties strongly change. The color changes, but also the solubility
properties change a lot. The sulfate salts loose water easily, but no acid
(H2SO4 or SO3).
Description:
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Heat the following chemicals, until absolutely no water is produced anymore:
1) vanadyl sulfate
2) chrome alum
3) nickel sulfate
4) cobalt sulfate
5) copper sulfate
All of these chemicals are hydrated sulfates.
The result is as follows:
1) blue --> light blue
2) dark purple --> dark green
3) bright blue/green --> light yellow with a green tinge
4) red/brown --> purple
5) bright blue --> very pale blue, almost white
On prolonged heating, no acid fumes of H2SO4 or SO3 could be observed. The
temperatures, required to obtain these are much higher and are not reached in
this experiment.
The hydrated solids all dissolve in water easily. The dissolving of some of the
material in a large excess of water only takes minutes, especially with some
shaking.
When the dehydrated solids are added to water then all of them dissolve
noticeably more slowly, except the copper sulfate.
1) The vanadyl sulfate dissolves very slowly and only partially. The liquid
becomes bright blue and clear and a white precipitate remains. Even after days,
the precipitate still is not dissolved.
When the liquid is acidified with sulphuric acid, such that the acid
concentration is appr. 0.5 mol/l, then the white solid still does not
dissolve, even after several days of exposure to the acidic solution.
2) The chrome alum becomes insoluble. The liquid remains colorless and a green
solid remains at the bottom of the test tube.
3) The nickel sulfate finally dissolves completely, giving a totally clear
solution, but it takes a few days, before all is dissolved. The solution is
light green, as expected for a nickelous solution.
4) The cobalt sulfate slowly dissolves, but it takes a very long time. After
several hours, the purple solid has dissolved and the liquid is bright
red/rose.
5) The copper sulfate immediately becomes blue again and dissolves quickly.