Description of experiment
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Needed compounds:
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hydrochloric acid : HCl
sodium sulfite : Na2SO3
hydrogen peroxide : H2O2
sodium bicarbonate : NaHCO3
copper sulfate penta hydrate : CuSO4 . 5H2O
Class:
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elem=Cu
precipitation
redox
Summary:
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Copper (II) salts give a cyan precipitate with bicarbonates. The color of
this precipitate is the same as the color of commercially available basic
copper carbonate.
This precipitate reacts with hydrogen peroxide, forming a dark green/brown
compound. With sulfite it also reacts, forming a brownish compound, which
on acidification dissolves, forming a light yellow/brown clear liquid.
Description:
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Add a solution of sodium bicarbonate to a solution of copper sulfate: A cyan
precipitate is formed. This precipitate does not appear instantaneously, it
takes a few seconds, before the liquid becomes completely opaque. There is
no visible effervescence of the liquid, but one can clearly hear a soft
hissing/bubbling noise, due to formation of many tiny bubbles. This gas
is carbon dioxide.
Split the liquid with the cyan precipitate in two parts.
Add some hydrogen peroxide (appr. 10% by weight) to one part of the liquid
with precipitate: The precipitate becomes dark green/brown. The liquid starts
bubbling fairly vigorously. After standing for a few hours, there still is
slow evolution of a gas, the precipitate has become dark brown.
Add a solution of sodium sulfite to the other part of the liquid with the
cyan precipitate: The precipitate changes color, it becomes green/yellow/
brown.
Add some hydrochloric acid: The liquid becomes clear and light yellow/brown.
A lot of gas is evolved (CO2, due to the bicarbonate).
Heat the liquid: No visible changes, except that some gas is expelled from
the liquid.