`color{green}("𝐈𝐭 𝐜𝐚𝐧 𝐛𝐞 𝐩𝐫𝐞𝐩𝐚𝐫𝐞𝐝 𝐛𝐲 𝐭𝐡𝐞 𝐟𝐨𝐥𝐥𝐨𝐰𝐢𝐧𝐠 𝐦𝐞𝐭𝐡𝐨𝐝𝐬:")`

(i) Acidifying barium peroxide and removing excess water by evaporation under reduced pressure gives hydrogen peroxide.

`color{red}(BaO_2 . 8 H_2O(s) + H_2SO_4 (aq) → BaSO_4(aq) +H_2O_2 (aq) +8H_2O(l))`

(ii) Peroxodisulphate, obtained by electrolytic oxidation of acidified sulphate solutions at high current density, on hydrolysis yields hydrogen peroxide.

`color{red}(2HSO_4^(-)(aq) oversettext(Electrolysis)→ HO_3SOOSO_3H (aq) oversettext(Hydrolysis)→ 2HSO_4^(-) (aq) + 2H^(+)(aq) + H_2O_2(aq))`

This method is now used for the laboratory preparation of `color{red}(D_2O_2)`

`color{red}(K_2S_2O_8(s) +2D_2O(I) → 2KDSO_4(aq) +D_2O_2(l))`

(iii) Industrially it is prepared by the autooxidation of 2-alklylanthraquinols.

`color{red}(text(2 ethylanthraquinol) underset(H_2//Pd) overset(O_2(air))⇄ H_2O_2 + text{(Oxidised product)})`

`color{green}(★)` In this case `color{red}(1% H_2O_2)` is formed. It is extracted with water and concentrated to `color{red}(~30%)` (by mass) by distillation under reduced pressure. It can be further concentrated to `color{red}(~85%)` by careful distillation under low pressure. The remaining water can be frozen out to obtain pure `color{red}(H_2O_2)`.

`color{green}(★)` In the pure state `color{red}(H_2O_2)` is an almost colourless (very pale blue) liquid.

`color{green}(★)` Its important physical properties are given in Table 9.4.


`color{green}(★)` `color{red}(H_2O_2)` is miscible with water in all proportions and forms a hydrate `color{red}(H_2O_2.H_2O)` (mp 221K).

`color{green}(★)` A `color{red}(30%)` solution of `color{red}(H_2O_2)` is marketed as `color{red}("100 volume")` hydrogen peroxide. It means that one millilitre of `color{red}(30% H_2O_2)` solution will give `color{red}("100 mL")` of oxygen at STP. Commercially marketed sample is `color{red}(10 V)`, which means that the sample contains `color{red}(3% H_2O_2).`

`color{green}(★)` Hydrogen peroxide has a non-planar structure. The molecular dimensions in the gas phase and solid phase are shown in Fig 9.3

`color{green}(★)` It acts as an oxidising as well as reducing agent in both acidic and alkaline media. Simple reactions are described below.


`color{green}("(𝐢) 𝐎𝐱𝐢𝐝𝐢𝐬𝐢𝐧𝐠 𝐚𝐜𝐭𝐢𝐨𝐧 𝐢𝐧 𝐚𝐜𝐢𝐝𝐢𝐜 𝐦𝐞𝐝𝐢𝐮𝐦")`

`color{red}(2Fe^(2+) (aq) + 2H^(+)(aq) + H_2O_2 (aq) → 2Fe^(3+) (aq) + 2H_2O(l))`

`color{red}(PbS(s) + 4H_2O_2 (aq) → PbSO_4 (s) + 4H_2O (l))`


`color{green}("(𝐢𝐢) 𝐑𝐞𝐝𝐮𝐜𝐢𝐧𝐠 𝐚𝐜𝐭𝐢𝐨𝐧 𝐢𝐧 𝐚𝐜𝐢𝐝𝐢𝐜 𝐦𝐞𝐝𝐢𝐮𝐦")`

`color{red}(2MnO_4^(-) + 6 H^(+) + 5H_2O_2 → 2Mn^(2+) + 8H_2O + 5O_2)`

`color{red}(HOCl + H_2O_2 → H_3O^(+) + Cl^(-) + O_2)`

`color{green}("(𝐢𝐢𝐢) 𝐎𝐱𝐢𝐝𝐢𝐬𝐢𝐧𝐠 𝐚𝐜𝐭𝐢𝐨𝐧 𝐢𝐧 𝐛𝐚𝐬𝐢𝐜 𝐦𝐞𝐝𝐢𝐮𝐦")`

`color{red}(2Fe^(2+) + H_2O_2 → 2Fe^(3+) + 2 OH^(-))`

`color{red}(Mn^(2+) + H_2O_2 → Mn^(4+) + 2 OH^(-))`

`color{green}("(𝐢𝐯) 𝐑𝐞𝐝𝐮𝐜𝐢𝐧𝐠 𝐚𝐜𝐭𝐢𝐨𝐧 𝐢𝐧 𝐛𝐚𝐬𝐢𝐜 𝐦𝐞𝐝𝐢𝐮𝐦")`

`color{red}(I_2 + H_2O_2 + 2 OH^(-) → 2I^(-) + 2H_2O+O_2)`

`color{red}(2MnO_4^(-) +3H_2O_2 → 2MnO_2 + 3O_2+2H_2O +2 OH^(-))`

`color{green}(★)` `color{red}(H_2O_2)` decomposes slowly on exposure to light.

`color{red}(2H_2O_2 (l) → 2H_2O(l) + O_2(g))`

`color{green}(★)` In the presence of metal surfaces or traces of alkali (present in glass containers), the above reaction is catalysed. It is, therefore, stored in wax-lined glass or plastic vessels in dark. Urea can be added as a stabiliser. It is kept away from dust because dust can induce explosive decomposition of the compound.

`color{green}(★)` Its wide scale use has led to tremendous increase in the industrial production of `color{red}(H_2O_2).`

`color{green}(★)` `color{green}("𝐒𝐨𝐦𝐞 𝐨𝐟 𝐭𝐡𝐞 𝐮𝐬𝐞𝐬 𝐚𝐫𝐞 𝐥𝐢𝐬𝐭𝐞𝐝 𝐛𝐞𝐥𝐨𝐰:")`

(i) In daily life it is used as a hair bleach and as a mild disinfectant. As an antiseptic it is sold in the market as perhydrol.

(ii) It is used to manufacture chemicals like sodium perborate and per-carbonate, which are used in high quality detergents.

(iii) It is used in the synthesis of hydroquinone, tartaric acid and certain food products and pharmaceuticals (cephalosporin) etc.

(iv) It is employed in the industries as a bleaching agent for textiles, paper pulp, leather, oils, fats, etc.

(v) Nowadays it is also used in Environmental (Green) Chemistry. For example, in pollution control treatment of domestic and industrial effluents, oxidation of cyanides, restoration of aerobic conditions to sewage wastes, etc.