M. EBERT 



The interpretation of these curves is aided by reference to Figure 3. It 

 can be seen that at doses which are very far below those needed for equiU- 

 brium vakies it is only at low oxygen tensions that the )ield depends on 

 oxygen tension. The curves of Figure 4 represent three stages with respect 

 to equilibrium values of hydrogen peroxide. Curve 1, in the pH range 

 4-8-9-0, shows that the dose was high enough so that the hydrogen peroxide 

 yield was at its equilibrium value, and therefore proportional to oxygen 

 concentration. At pH 4-2 (curve 2) the hydrogen peroxide yield was not at 

 equilibrium, but not far below. Curve 3, at pH 0-76, was of the form which 

 indicates a yield very far below equilibrium value. The rate of formation 

 of hydrogen peroxide at pH 0-76 was independent of the dissolved oxygen 

 for all oxygen-niti'ogen mixtures containing more than 3 per cent oxygen. 



As the equilibrium values are attained only with very high doses at low 

 pH, the back reaction was studied by the decomposition of hydrogen peroxide. 



10,000 



o 



2,000 



1,000 



500 



ZOO 



100 



SO 



10 



xlO rad. 

 Figure 5. HgOg decomposition in neutral and acid solutions 



X 70^ rad. 



Figure 5 shows that the rate of decomposition of hydrogen peroxide was 

 independent of pH if oxygen was bubbled. When nitrogen alone was used, 

 the decomposition of 0-01 M hydrogen peroxide was carried to completion 

 with a dose of 4 x 10*^ rad at pH 6, whereas at pH 2 the decomposition was 

 much slower and appeared to approach equilibrium. In the reaction 

 scheme suggested the break-down of hydrogen peroxide into molecular 

 oxygen goes via the reaction 



H2O2 + O2" ->OH + OH- + O2 .... (6) 



This follows the only reaction which is pH dependent 



H02^H+ +O2- or H02 + OH-->H20+02- .... (5) 



so that at low pH the rate of reaction (6) will be much reduced and molecular 

 oxygen will therefore be lost very slowly. 



Even in acid solutions decomposition of hydrogen peroxide takes place 

 via reactions (4) and (7), but the forward reactions (2) and (3) are still able 



35 



