228 Artctl.t~riccc Chhiccc Aclct. 69 ( 1974) 228-230 c’. Elscvicr Scientific Publishing Company. Amsterdam - Printed in The Ncthcrhmds

SHORT COMMUNICATION

The decomposition of hydrogen peroxide in alkaline solution

0. A. OHLWEILER and J. 0. MEDITSCH Imsrir~rro tic QII~I~I~CYJ. UFRGS. Porro Alegw (Brctsil)

(Rcccivcd 28th June 1973)

Hydrogen peroxide is often used as an oxidizing agent in alkaline medium. The excess can be decomposed by boiling the alkaline solution, particularly in the presence of platinized platinum, but prolonged boiling is necessary to destroy the last traces of hydrogen peroxide. In a micromethod for the determination of chromium’, to overcome this prolonged boiling period, chlorine water was added, followed by potassium cyanide to remove the excess of chlorine. More frequently, the decomposition of hydrogen peroxide is hastened by the addition of appropriate catalysts. Feigl er (11. ‘, for instance, oxidized chromium(III) in alkaline solution with hydrogen peroxide. and removed the excess of peroxide by boiling with some nickel salt (5 ml of 5’%, nickel nitrate solution). The catalytic action of osmium tetroxide is much better, mere .traces being needed to destroy the hydrogen peroxide at room temperature in a few minute$.

In the work described here, the decomposition of hydrogen peroxide in alkaline solution was examined in relation to a procedure for the determination of silica in silicates, in which the sample melt from a boron trioxide-lithium carbonate fusion is dissolved in dilute hydrochloric acid containing hydrogen peroxide4; the peroxide serves to convert any titanium(IV) to the perhydroxy complex, thus preventing its interference. After the removal of interferences by ion exchange, the excess of hydrogen peroxide must be destroyed before the final stages of the analysis4. Some methods of solving this practical problem are compared below. The observations may be useful in other cases.

A sample solution was prepared by mixing 1 ml of perhydrol with 1 I of distilled water. A 50 ml aliquot was acidified with 20 ml of 1.5 M sulfuric acid and then titrated with co. 0.1 N potassium permanganate solution. This titration value was used for comparison to establish the relative amounts of hydrogen peroxide destroyed by the methods studied.

For each test, a 50-m] aliquot of the hydrogen peroxide solution was treated with 1 g of sodium hydroxide, and the particular decomposition method was applied. Then the solution was acidified with 25 ml of 1.5 M sulfuric acid and titrated with 0.1 N potassium permanganate solution.

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The solution of osmium(VIII) employed as catalyst was the usual 0.25% osmium tetroxide in 0.05 M sulfuric acid; 2 drops were used for the test.

The ultrasonic generator had the following characteristics: operation fre- quency. 20 kHz; cavitation bath, 16 cm diameter. 10 cm height; power density in the cavitation bath, 2 W cm- ‘.

The results obtained with the different decomposition treatments for hydrogen peroxide are shown in Table I. It can be seen that decomposition of hydrogen peroxide by simple heating on a water bath is slow; a considerable portion remains undecomposed after 1 h. The relative amount destroyed depends on the time of heating, but also varies with the particular glassware used. The effect of ultrasonics at a power density of 2 W cmd2 is very small.

TABLE I

DECOMPOSITION OF HYDROGEN PEROXIDE IN ALKALINE SOLUTION

Hating on :I water bilth

Action of ultrasonics Leaving in platinum dish ut room tcmpcroturc Leaving in platinum dish with application or ultrasonics Heating in platinum dish on u water bath Addition of 0~0, and waiting iIt room tcmpcraturc Addition of 0~0, and application of ultrasonics Addition of 0~0, and hating on wutcr bath

---

30 69.0 60 93.4 90 86.8 15 1.8

I.5 72.6

10 79.2 10 96.X I5 97.9 2 99.0 5 100 I 99.6 1.5 100

2 100 --. -

A large part of the hydrogen peroxide can be decomposed simply by allowing the solution to stand in a platinum dish at room temperature for a reasonable period of time. The decomposition is catalysed by contact with the walls of the platinum dish. The rate of decomposition increases appreciably with simultaneous application of ultrasonics and, more notably, with heating of the solution.

The decomposition of hydrogen peroxide is extraordinarily accelerated by the catalytic effect of osmium tetroxide, only traces of which are needed. At room temperature, 5 min suffices for complete decomposition. Further experiments showed that solutions 5 times richer in hydrogen peroxide are still completely decom- posed at room temperature in the course of 5 min. Occasionally, no evolution of gaseous bubbles is observed; since the solution does not consume permanganate,

230 SHORT COMMUNICATION

the oxygen presumably forms a supersaturated solution and in fact, the application of ultrasonics to the solution after 5 min causes a prompt effervescence. The rate of decomposition in the presence of osmium tetroxide is significantly increased by the simultaneous application of ultrasonics or heat. The addition of more than 2 drops of osmium tetroxide solution can also be used to accelerate the decompo- sition

REFERENCES

1 E. S. Schulek and M. S. Szakzlcs, Acttc Chim. Acutl. Sci. Hurry., 4 (1954) 457. 2 F. Fcigl. K. Klanfcr and L. Wcidcnfcld, Z. Amrl. Cl~em.. 80 ( 1930) 5. 3 J. H. van dcr Meulcn. Rec. Trcrr:. Chiut. Pay-Bas. 58 (1939) 553. 4 0. A. Ohlwcilcr. J. 0. Mcditsch, S. Santos and J. A. Odcrich. Ard. Chirn. Actct. 68 (1974) 225.