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Oxidation of tartraric acid catalysed by cobalt

In this experiment is shown , that hydrogen peroxide itself very slowly oxidises tartraric acid, but adding a small amount of a cobalt-salt, in this case cobalt chloride hexahydrate will give a vigorous reaction.
 
Needed equipment:
-test tube
 
Chemicals:
-6% hydrogen peroxide (dilute 1 volume 30% hydrogen peroxide with 4 volumes of water)
-A tartrate, preferably potassium sodium tartrate or other dibasic tartrate but I used tartraric acid
-A cobalt(II)-salt (e.g. cobalt chloride hexahydrate, cobalt sulfate heptahydrate or cobalt nitrate hexahydrate)
 
Safety:
-6% hydrogen peroxide is an irritant. In case the 6% solution is prepared from concetrated (30-35%) hydrogen peroxide one must take care as Hydrogen peroxide at this concentration is corrosive.
-Cobalt salts are quite toxic and are possibly mild carcinogens by inhalation.
-It's best to not heat over about 70-80C as the reaction may become so vigorous that the liquid foams out of the test tube.
 
Experiment:
 
Prepare a (approx 5%) solution of potassium sodium tartrate (or react 1 eq. tartraric acid with 2 eq. NaOH). Also prepare a 6% solution of hydrogen peroxide. Add about 1,5 volume ( I used about 4mL) of the tartrate solution to 1 part hydrogen peroxide solution (about 3mL). heat to 70C. No visible reaction is observed. Add a small amount (approx 50-100mg) of cobalt chloride hexahydrate (or an other suitable cobalt salt) dissolved in a mL of water. After a short delay a vigorous reaction is observed, wich becomes more and more vigorous. The solution becomes green. A lot of gas is evolved.
 

YouTube Video

 
The temperature is determing the violence of the reaction. At room temperature, the reaction is a lot slower.
 
I wanted to determine whether the gas is just oxygen (decomposition of hydrogen peroxide by cobalt/tartrate complex) or if there's a large quantity of carbon dioxide present (oxidation of tartratic acid).
This was done by bubbling the gas in a NaOH/CaCl2-solution (I do not own any Ca(OH)2 or Ba(OH)2.8H2O. This yeilded a good amount of precitipate (CaCO3) indicating production of carbon dioxide by the cobalt-catalysed reaction.
 
Discussion
 
It is said that cobalt forms a peroxo-complex (brown) in the presence of hydrogen peroxide, wich is the oxidised (by hydrogen peroxide) to a superoxo-complex.
The complex is 2 cobalt(III)-ions linked by a superoxo-group. Both cobalt(III)-ions are coordinated to both 2 tartrate-ions as well, and they also share one tartrate-ion.
This complex oxidises the tartrate.
 
The netto reaction goes as follows:
 
-OOCCH(OH)CH(OH)COO- + 3 H2O2 --Co(II)--> 2 CO2 + 2 HCOO- + 4 H2O
 
A very good reference, wich also explains the structure of the complex:
 
 
 
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