Describe the preparation of Hydrogen peroxide and write its physical properties.

(N/A) $(i)$ Acidifying barium peroxide and removing excess water by evaporation under reduced pressure gives hydrogen peroxide.
$BaO_{2} \cdot 8H_{2}O_{(s)} + H_{2}SO_{4_{(aq)}} \longrightarrow BaSO_{4_{(s)}} + H_{2}O_{2_{(aq)}} + 8H_{2}O_{(l)}$
$(ii)$ Peroxodisulphate,obtained by electrolytic oxidation of acidified sulphate solutions at high current density,on hydrolysis yields hydrogen peroxide.
$2HSO_{4_{(aq)}}^{-}$ $\xrightarrow{\text{Electrolysis}} HO_{3}SOOSO_{3}H_{(aq)}$ $\xrightarrow{\text{Hydrolysis}} 2HSO_{4_{(aq)}}^{-} + 2H_{(aq)}^{+} + H_{2}O_{2_{(aq)}}$
This method is now used for the laboratory preparation of $D_{2}O_{2}$.
$K_{2}S_{2}O_{8_{(s)}} + 2D_{2}O_{(l)} \longrightarrow 2KDSO_{4_{(aq)}} + D_{2}O_{2_{(l)}}$
$(iii)$ Industrially,it is prepared by the auto-oxidation of $2$-alkylanthraquinols.
(2-ethyl anthraquinol) $\underset{\text { Oxidation }}{\stackrel{\text { Reduction }}{\rightleftharpoons}} H _2 O _2+$ (Oxidised product)
In this case,$1\%$ $H_{2}O_{2}$ is formed. It is extracted with water and concentrated to $\sim 30\%$ (by mass) by distillation under reduced pressure.
It can be further concentrated to $\sim 85\%$ by careful distillation under low pressure. The remaining water can be frozen out to obtain pure $H_{2}O_{2}$.
In the pure state,$H_{2}O_{2}$ is an almost colourless (very pale blue) liquid.
$H_{2}O_{2}$ is miscible with water in all proportions and forms a hydrate $H_{2}O_{2} \cdot H_{2}O$ ($mp$ $221 \ K$).
Physical Properties of Hydrogen Peroxide:

Property	Value
Melting point/$K$	$272.4$
Density (liquid at $298 \ K$)/$g \ cm^{-3}$	$1.44$
Boiling point (extrapolated)/$K$	$423$
Viscosity $(290 \ K)$/centipoise	$1.25$
Vapour pressure $(298 \ K)$/$mmHg$	$1.9$
Dielectric constant $(298 \ K)$	$70.7$
Density (solid at $268.5 \ K$)/$g \ cm^{-3}$	$1.64$
Electrical conductivity $(298 \ K)$/$\Omega^{-1} cm^{-1}$	$5.1 \times 10^{-8}$