question_answer

Account for the following in the preparation of \[{{H}_{2}}{{O}_{2}}\] from barium peroxide \[(Ba{{O}_{2}})\] and dilute \[{{H}_{2}}S{{O}_{4}}\]. (a) A thin paste of hydrated barium peroxide is used instead of anhydrous peroxide. (b) The temperature of the reaction mixture is kept at 0°C. (c) The final solution must be kept slightly acidic.

Answer:

                (a) Anhydrous \[Ba{{O}_{2}}\] is not used because the reaction with dilute\[{{H}_{2}}S{{O}_{4}}\] is highly exothermic and will accelerate the decomposition of \[{{H}_{2}}{{O}_{2}}\] into \[{{H}_{2}}O\] and \[{{O}_{2}}\]. Moreover, in this case a layer of \[BaS{{O}_{4}}\] initially formed in the reaction gets deposited over barium peroxide and any further reaction with acid does not take place. Keeping this in mind, hydrated barium peroxide \[(Ba{{O}_{2}}.8{{H}_{2}}O)\] is used. (b) The temperature of the reaction mixture is kept at 0°C because higher temperature will cause the decomposition of hydrogen peroxide. (c) The traces of \[{{H}^{+}}\] ions present in the final solution will act as inhibitor and will retard the decomposition of \[{{H}_{2}}{{O}_{2}}\].