I know this has been discussed so well by others. But I was curious about doing it once again.
So just ignore if you don't want to hear it again
Chevreul's salt is a peculiar salt of copper characterised by the exhibition of Two oxidation states by the same compound
That is copper exhibit both +1 and +2 oxidation state
This makes chevreul salt special.
Otherwise continue.
Looking into the history we find that
this salt was prepared the first time in 1812 by a French chemist Michel Eugene Chevreul.
Preparation of Chevreul's salt
Chevreul's salt is very easily prepared by mixing equimolar solution of Copper II sulfate and Potassium Metabisulfite
You can very easily get both these compounds
Copper sulfate is sold as a weedicide . You can get it from any agri shops.
You can also buy the potassium metabisulfite online like eBay or Amazon.
On mixing both these solution,the blue colour turns to green. Probably because there's formation of a yellow complex which along with the blue colour
of cu2+ appear as beautiful emerald green color .
Now heat the solution to a gentle boil. On increasing the temperature you see the color turns darker and darker and eventually a brick red precipitate
is formed.
Now let it cool and filter the solution to get the precipitate. Air dry the precipitate and there you have it... Chevreul's salt .
Exact mechanism is said to occur in multiple steps
Initial step
The metabisulfite gets decomposed by heat to form sulfite and sulfur dioxide
Then
The potassium sulfite react with copperII sulfate to form copper II sulfite .
Sulfur dioxide now react with copper II sulfite to form copper I sulfite and sulfur trioxide.As soon as a molecule of copper I sulfite is formed the
copper II sulfite avidly binds to it to form Copper I,II sulfite (Chevreul's salt).
Both the oxidation states can be tested using two compounds
Initially I add some dilute HCl to chevreul's salt. You immediately see a white compound formed. That is copper I chloride
( Take care not to use concentrated or excess acid
So copper II chloride can form and solution turns green)
Now add some chevreul's salt to ammonium hydroxide blue colour is obtained due to formation of tetraamine copper II complex where Copper has +2
oxidation state. A complex is also formed with +1 but it's colourless.
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