Hydrogen Peroxide in Cleansing Antiseptics John D. Worley St. Norbert College, DePere, WI 541 15 An experiment suggested by O'Connor and others in a recent article suggests the use of a simple gas collection apparatus for the determination of hicarhonate in Alka-Seltzer".' Our students have carried out this experiment with excellent results and always enjoy :he practical aspects of the exercise. For our own articular interests. and because we wanted to involve an oxidation-reduction reaction, we have modified O'Connor's ~ r o c e d u r esliehtlv " .and have aoolied .. the "eas collection apparatus to a different purpose. There are a number of cleansine antise~ticson the market which are used as mouthwash a&or foi treatment of cold sores (canker sores). The active ingredient in most of these preparations is hydrogen peroxide. The vehicle is usually carbamide peroxide, an inclusion comoound of urea and HnO,>. in a glycerol base. Upon contact with'the saliva the decomposes to water and oxygen. The oxygen effervescence gives a mechanical cleansing action. For our experiment we used Marion Laboratory's Gly-Oxide', which we obtained from a local drugstore. The bottle's label indicates that the preparation contains 10% carbamide peroxide in a glycerol base. Our interest was to determine the peroxide content by measuring the volume of oxygen released when the peroxide was oxidized by permanganate. ~
~
~~~~
Procedure We used a 125-ml Erlenmeyer flask containing a stirring bar. We added 50 ml of standard potassium permanganate (1.8995 X 10W M ) and 50 ml of 2 M sulfuric acid. A small polyethylene cap of the type used for closing weighing vials was accurately weighed to the nearest 0.1 mg. About 15 drops of the Gly-Oxide" preparation were placed in the center well of the cap and the mass determined by difference. The cap was carefully lowered through the neck of the Erlenmeyer flask by means of tweezers. The system was closed, checked for leaks, and the initial vvlume noted on the 50-ml buret. Temperature and barometric pressure were recorded. After these preliminaries, the stirring motor was turned on high. The cap's contents were mixed with the permanganate-acid solution and the reaction commenced. The reaction reauired a~oroximatelv .. 15 min to reach eouilibrium. There are no safetv hazards associated m i 1 1 1 I I I ~ , rpcrlmrm ~ - . I tr .,..a.r.,,rc n u i r c H~mtvcr, sludrnr. . n d d . t h v x \ . l w ~ ~ r nth.,r 1 4i.unwnlratcd nrroxides should he handled with great care, particularly when they are to he mixed with a strong oxidizing agent such as permanganate. ~
~~
~
~
' Peck, L., Irgolic, K., and O'Connor, R., J. CHEM.EDUC., 57, 517 (1980).
"The Merck index." 8th Ed., Merck and Go., inc., Rahway, NJ: 1968, p.
1095.
Ramette, R., "Chemical Equilibrium and Analysis," Addison-Wesley Publishing Co.. Reading, MA, 1981 p. 24 (problem 15).
678
Journal of Chemical Education
Discussion Trials were made by three persons with each person making two determinations. The data are illustrated by the following table. The molecular weight of carhamide peroxide is 94 g/ Exoerimental Data Mass Giy-Oxidea (1) Mass Gly-Oxidea(2)
Percent Peroxide (1) Percent Peroxide (2) Avg.
0.5228 g 0.6465 g 10.61 10.10 10.36 f 0.26
0.6831 g 0.6797 g 9.33 10.19 9.78 0.43
*
0.7022 g 09100 g 10.03 9.72
9.88 i 0.16
mole.2 We have assumed a 1:l relationship between the urea and the Hz02 and that the peroxide is oxidized by permanganate according to the equation,
-
6H+ t 533202 + 2MnOp-' 502 + 2Mnt2 t 8HaO This method also works verv well usine commercial HqO? samples. The aqueous peroxide solutionscan he titratedhi; rectlv with permanpanate to provide a check on the gas collection method. A s a n example, a sample taken from our stockroom refrigerator hearing the Mallinckrodt label was titrated. The bottle's label inaicated that it was a 30% hy weight aqueous solution of HzOz.Four drops (0.1160g) of the peroxide solution were added to a 125-ml Erlenmeyer flask. After adding 100 ml of 1M sulfuric acid, titration with standard potassium permanganate required 22.70 ml of 1.8995 X 1 0 V M permanganate solution. The percent hydrogen peroxide was determined to be 31.6%. The experiment was repeated using the gas collection method nreviouslv described. Four d r o ~ of s the ~ e r o x i d esolution were weighed into a polyethylene cap equipped with a small elass cover of the tvoe used for meltine ooint determinations. The mass of thk'peroxide solutionkas 0.1229 g. The can was added to a flask containine 50 ml ~ermaneanate solution and 50 m12 M sulfuric acid. The vol;me of oxygen evolved was 27.65 ml a t 22OC. This volume of oxveen .- corresponds to a %Hz02 of 30.6%. Glv-Oxidea cannot be checked hv titration with permanganate because it contains a glycerol base which is siowly oxidized by the permanganate and no sharp endpoint can he obtained.
Acknowledgment I thank Professor David Klopotek for helpful discussions on the nature and structure of carbamide neroxide. Students Jay McCormick and Tom Londo carried out two of the three trials in connection with the Glv-Oxidea determinations. The hydrogen peroxide experiment was inspired by a problem from Professor Richard Ramette's new book."
