Ncert Solutions Chemistry Class 11th

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Hydrogen peroxide cannot be concentrated by heating as it can cause bumps on heating. It can be extracted with water and concentrated to ~30% (by mass) by distillation under reduced pressure. It can be further concentrated to ~85% by careful distillation under low pressure. The remaining water can be frozen out to obtain pure H₂O₂.

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Water has a significantly higher boiling point than hydrogen sulphide because of the presence of strong hydrogen bonds between water molecules, which are absent in hydrogen sulphide due to the lower electronegativity of sulfur compared to oxygen; this means more energy is required to separate water molecules, resulting in a higher boiling point. 

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Water molecules are polar because in the gas phase water is a bent molecule with a bond angle of 104.5°, O-H bond length of 95.7 pm. Oxygen is more elsectronegative  (EN = 3.5 ) than hydrogen (EN= 2.1 ) hence, O-H bond is polar . In the water molecule, two polar O-H nonds area present which are held together at an angle of 104.5 . Due to the resultant of these two dipoles, water molecule is polar and has an dipole moment of 1.84 Debye.

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H₂O₂ decomposes slowly on exposure to light.

2H₂O₂→ 2H₂O+2O₂

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.

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(i) Oxidising action in acidic medium:

2Fe²⁺ (aq)+2H⁺ (aq)+H₂O₂ (aq) → 2Fe³⁺ (aq)+2H₂O (l)

PbS (s)+4H₂O₂ (aq) → PbSO₄ (s)+4H₂O (l)

(ii) Reducing action in acidic medium:

2MnO₄^-+6H⁺+5H₂O₂ → 2Mn²⁺+8H₂O+5O₂

HOCl+H₂O₂ → H₃O⁺+Cl^-+H₂O

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H₂O₂ structure in gas phase, dihedral angle is 111.50. H₂O₂ structure in solid phase at 110 k, dihedral angle is 90.20.

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Heavy water can be used as a moderator in nuclear reactors and in exchange reactions for the study of reaction mechanisms. It can be prepared by exhaustive electrolysis of water or as a by-product in some fertilizer industries.

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Hydrogen economy (Hydrogen as fuel):

(i) The electricity cannot be stored in automobiles. It is not possible to store and transport nuclear energy. Hydrogen is an alternative source of energy and hence called the 'hydrogen economy". Hydrogen has some advantages as fuel.

(ii) Available in abundance in combined form as water.

(iii) On combustion produces H₂O. Hence, pollution free.

(iv) H₂O₂ fuel cells give more power.

(v) Excellent reducing agent. Therefore, it can be used as a substitute of carbon in reduction for processes in industry.

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In sodium the last shell electron is in 3s₁ after losing that electron, it can acquire the configuration of Ne. Whereas in hydrogen, the electron is in s-orbital.

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Because of ionization enthalpy, hydrogen resembles more with halogens, is 520 kJ mol^-1, F is 1680 kJ mol^-1and that of His 1312 kJ mol^-1. Like halogens, it forms a diatomic molecule, combining with elements to form hydrides and a large number of covalent compounds.