A procedure of…

By Zachary James

…Chevreul’s Salt

Chevreul's Salt is a little-known copper compound that is quite easy to prepare, and has a few very interesting properties.

This experiment only requires two materials: copper sulfate and sodium metabisulfite. The former is sold at hardware stores as root killer for plumbing, and the latter is commonly found on eBay (since it is used by gold recovery people).

STEPS

The Complete Procedure(to be honest, I actually just copied this from the internet)

Step 1

First, make two solutions:• 2.4g CuSO4 · 5H2O in 25mL distilled water

• 2.0g Na2S2O5 in 10mL distilled water

_______________________________________This yielded a light blue solution and a colorless one. Combing the two solutions together creates a

e emerald one.

Step 2• Next, the solution needs to be

boiled for several minutes. The solution steadily darkens, and once it reaches boiling temperature a brick red solid precipitates. It is a very nice crystalline precipitate that easily and quickly settles to the bottom of the test tube. This is Chevreul's Salt - Cu3(SO3)2 · 2H2O.

My yield was 1 gram of dark brick red crystalline powder.

Chevreul's salt is interesting for two reasons. One is its color. Just about all copper compounds are green or blue in color, and there are very few exceptions to that. So it's neat to see copper in a color like this. Second is the fact that it is a mixed valence compound. Take a look at the formula for the salt above - you'll notice that the charge only balances if some of the copper atoms are in the +1 state and some are in the +2 state! I.E. there is a +4 charge divided over 3 copper atoms. Perhaps a more descriptive formula for this compound is CuSO3·Cu2SO3·2H2O.

That’s it.But go to the next slide for testing.

Testing

Copper I mixtureFirst, I wanted to show that Chevreul's

Salt does indeed have both copper(I) and a copper(II) behaviors. The first test (left picture below) was to take a small spatula-full and add dilute hydrochloric acid. This precipitates copper(I) chloride as a white solid. I used dilute acid here because CuCl can redissolve in excess acid.

Copper II mixtureThe second test (right picture

below) was to add a similar amount to concentrated ammonia solution. This dissolves the salt and changes color to a deep blue. This is the commonly-seen ammonia complex with copper(II): hexaaminecopper(II).

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