With the help of suitable examples, explain the property of $\mathrm{H}_2 \mathrm{O}_2$ that is responsible for its bleaching action?
The bleaching action of hydrogen peroxide is due to the nascent oxygen which it liberates on decomposition.
$$\mathrm{H}_2 \mathrm{O}_2 \longrightarrow \mathrm{H}_2 \mathrm{O}+[\mathrm{O}]$$
The nascent oxygen combines with colouring matter, in turn, gets oxidised. Thus, the bleaching action of $\mathrm{H}_2 \mathrm{O}_2$ is due to the oxidation of colouring matter by nascent oxygen. It is used for the bleaching of delicate materials like ivory, feathers, silk, wool etc.
Colouring matter $+[\mathrm{O}] \longrightarrow$ Colourless matter
Why is water molecule polar?
Oxygen is more electronegative $(\mathrm{EN}=3.5)$ than hydrogen $(\mathrm{EN}=2.1)$ hence, $\mathrm{O}-\mathrm{H}$ bond is polar. In the water molecule, two polar $\mathrm{O}-\mathrm{H}$ bonds are present which are held together at an angle of $104.5^{\circ}$. Due to the resultant of these two dipoles, water molecule is polar and has an dipole moment of 1.84 Debye.
Why does water show high boiling point as compared to hydrogen sulphide? Give reasons for your answer.
Water show high boiling point as compared to hydrogen sulphide due to high electronegativity of oxygen ( $\mathrm{EN}=3.5$ ). Water undergoes extensive H - bonding as a result of which water exists as associated molecule.
For breaking these hydrogen bond, a large amount of energy is needed and hence the boiling point of $\mathrm{H}_2 \mathrm{O}$ is high.
In other words, due to lower electronegativity of $S(E N=2.5)$, hydrogen sulphide do not undergo H -bonding. Consequently, $\mathrm{H}_2 \mathrm{~S}$ exists as discrete molecule and hence its boiling point is much lower than that of $\mathrm{H}_2 \mathrm{O}$. Thats why $\mathrm{H}_2 \mathrm{~S}$ is a gas at room temperature.
Why can dilute solutions of hydrogen peroxide not be concentrated by heating? How can a concentrated solution of hydrogen peroxide be obtained?
Dilute solutions of $\mathrm{H}_2 \mathrm{O}_2$ cannot be concentrated by heating because it decomposes much below its boiling point.
$$2 \mathrm{H}_2 \mathrm{O}_2 \longrightarrow 2 \mathrm{H}_2 \mathrm{O}+\mathrm{O}_2$$
$1 \% \mathrm{H}_2 \mathrm{O}_2$ 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 $\mathrm{H}_2 \mathrm{O}_2$.
Why is hydrogen peroxide stored in wax lined bottles?
Hydrogen peroxide is decomposed by rough surfaces of glass, alkali oxides present in it and light to form $\mathrm{H}_2 \mathrm{O}$ and $\mathrm{O}_2$.
$$2 \mathrm{H}_2 \mathrm{O}_2 \longrightarrow 2 \mathrm{H}_2 \mathrm{O}+\mathrm{O}_2$$
To prevent this decomposition, hydrogen peroxide is usually stored in paraffin wax coated plastic or teflon bottles.