Why is hydrated barium peroxide used in the preparation of hydrogen peroxide instead of anhydrous barium peroxide ?

Explanation

(a) If anhydrous barium perioxide is used in the preparation of `H_(2)O_(2)` , the `BaSO_(4)` formed during the reaction forms an insoluble protective coating on the surface of solid barium peroxide . This prevents
`BaO_(2) (s) + H_(2)SO_(4)(aq) to BaSO_(4) (s) + H_(2)O_(2) (aq)`
further action of the acid and utlimately the reaction stops. If, however, hydrated barium peroxide (in the form of thin paste) is used, the water of crystallization does not allow `BaSO_(4)` to deposit on the surface of `BaO_(2)` and the reaction goes to completion.
(b) The aqueous solution of `H_(2)O_(2)` prepared by the action of dil. `H_(2)SO_(4)` on hydrate `BaO_(2)` has impurities of heavy metal ions like `Ba^(2+),Pb^(2+), ` etc. These catalyse the decomposition of `H_(2)O_(2)` . Therefore, `H_(2)O_(2)` prepared by the action of dil. `H_(2)SO_(4)` on hydrated `BaO_(2)` does not have good keeping qualities . If, however, phosphoric acid is used, the impurities of heavy metal ioins are precipitated as insoluble phosphates. As a result, the resulting solution of `H_(2)O_(2)` has good keeping qualities.
(c) Oxidising agent : `2 Cr(OH)_(3) + 4NaOH + 3H_(2)O_(2) to 2Na_(2)CrO_(4) + 8H_(2)O`
Here, `Cr^(3+)` gets oxidised to `Cr^(6+)`
Reducing agent : `2K_(3)[Fe(CN)_(6)]+2KOH + H_(2)O_(2) to 2K_(4)[Fe(CN)_(6)]+2H_(2)O+O_(2)`
Here, `Fe^(3+)` gets reduced to `Fe^(2+)`.