edited by GEORGE L. GILBERT
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A Versatile Kinetics Demonstration Submitted by: Paul T. R u d a Clevrland Hill Schools Cheektowaga, New York Checked by: George Virtes Wnrd Mdoille H.S. Setauket, New York The oxidation of tartaric acid by hydrogen peroxide in the presence of a cohalt chloride catalyst provides a reaction that can he used in a variety of kinetics demonstrations. Solution Preparation (Sinzle
(Stock ~olution) 25g/300ml83.3g/ l000ml 20ml30?6/ lOOml30%/ RU*)
1) Potassium Sodium Tartrate KNaC4H40r;4H20(aq) 2) 6% H , A ( a d
(USE CAUTION I N HANDLING T H E 30% H202) Note: The 3096 hydrogen peroxide is a danger and you may wish to utilize a 6% solution that is available commercially. It is known as 20 volume hydrogen peroxide and is available as a hair care product. An example is Clairoil Clairoxide Liquid Developer. 3) CoCla (aq) 1.0g/25ml 10g/250ml Procedure Prepare two beakers, one as a control. 1) In a 600-1000 ml beaker mix a ) 300 ml of potassium sodium tartrate (aq) h) 100 ml of the 6% H z 0 2 (aq) 2) Cover with a watch glass and heat on a hot plate to desired temperature (.50-7O0C). 3) Remove from the heat and add the catalyst to one of the beakers. Cover and ohserve. Take precautions in case the beaker should overflow. T h e reaction is very vigorous a t higher temperatures. Utilization 1) Cntalysis. This reaction shows, in a dramatic way, the effect a catalyst has on the rate of reaction. The reaction is very slow until the catalyst is added. The evolution of C02 (g) is slow even at. higher temperatures. 2) Artiuated Compl~x.The demonstration clearly shows the role of an activated complex in a reaction mechanism. The catalyst is pink. When it is added to the reaction mixture the Tested Demonstrations is a monthly feature designed to present lecture demonstrations and experiments in a format convenient.for classroom use. Readers interested in either suhmitting or checking demonstrations shoold contact the column editor. An outline of format reqniremmts was given on page 166 of the March 197fi issue of This .lournnl. ~~
652 1 Journal of Chemical Education
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cohalt forms a green complex with the tartrate. The reaction is mostvi~orousa t this point. As the tartrate isoxidized, the activated complex is destroyed and the catalyst is reformed. At this point the mixture regains its pink color. 3) TheEffect of Tempernture on Renction Rate. Thisdemonstration can be used to show this relationship by timing the pink green pink change. The timer is started upon addition of thr cat,alyst and is stopped when the catalyst is regenerated. The times range from approximately 100 sec a t 50-C to 30 sec a t 70%.
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References Thompron. .Jon, roirirodo Science Teaehsrs Associnfinn Neuislelfer, 20,[8]. (May 1876). D~roo,laliui. The Seirnee Teacher. 41. (11 (January (19741.
