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Hydrogen grade - 11 ncert cbse


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Hydrogen By Niraj 10 - N H 1 Hydrogen 1.00794 1s 1


Hydrogen First element in the periodic table Consists of one proton and one electron Electronic configuration is Hydrogen is placed separately placed in the periodic table due to its resemblance to alkali metals (same configuration and forms uni-positive ions, oxides, halides and sulphides) and halogens (forms uni-negative ions, high ionization enthalpies and forms hydrides, diatomic molecules and covalent compounds)   2

Isotopes of Hydrogen:

Isotopes of Hydrogen Property Hydrogen(Protium) Deuterium Tritium Relative abundance (%) 99.985 0.0156 10 -15 Relative atomic mass (g/mol) 1.008 2.014 3.016 Melting point (K) 13.96 18.73 20.62 Boiling point (K) 20.39 23.67 25 Density (g/L) 0.09 0.18 0.27 Enthalpy of fusion (kJ/mol) 0117 0.197 - Enthalpy of vaporization (kJ/mol) 0.904 1.226 - Internuclear distance (pm) 74.14 74.14 - Ionization enthalpy (kJ/mol) 1312 - - Electron gain enthalpy (kJ/mol) -73 - - Covalent radius (pm) 37 - - Ionic radius (pm) 208 - - 3

Dihydrogen - h2:

Dihydrogen - h 2 It is the most abundant element in the universe (70% of the total mass of the universe) and is the principal element in the solar atmosphere 4

Properties of Dihydrogen:

Properties of Dihydrogen Physical Properties Colourless, odourless, tasteless and combustible gas Lighter than air Insoluble in water Chemical Properties Inert at room temperature due to high H-H bond enthalpy Reacts with halogens to give hydrogen halides Reacts with oxygen to form water, this reaction is highly exothermic Reacts with dinitrogen to form ammonia It combines with many metals at a high temperature to produce corresponding hydrides Reacts with organic compounds in the presence of catalysts to give hydrogenated products, for e.g. – Hydrogenation of vegetable oils using nickel as catalyst gives edible fats 5

Preparation of Dihydrogen:

Preparation of Dihydrogen Laboratory preparation of dihydrogen It is usually prepared by the reaction of granulated zinc with dilute hydrochloric acid It can also be prepared by the reaction of zinc with aqueous alkali Commercial production of dihydrogen Electrolysis of acidified water using platinum electrodes gives dihydrogen High purity dihydrogen (>99.95%) is obtained by electrolysing warm aqueous barium hydroxide solution between nickel electrodes It is also obtained as a by- produ ct in the manufacturing of sodium hydroxide and chlorine by the electrolysis of brine solution Reaction of steam on hydrocarbons or coke at high temperature in the presence of catalyst gives dihydrogen 6

Uses of Dihydrogen:

Uses of Dihydrogen Used in the synthesis of ammonia which is then used to manufacture of nitric acid and nitrogenous fertilizers Used in the manufacture of Vanaspati fat by the hydrogenation of polyunsaturated vegetable oils like soybean, cotton seeds etc. Used in the manufacture of bulk organic chemicals, mainly methanol Widely used for the manufacturing of metal hydrides Used for the preparation of hydrogen chloride For metallurgical processes, it is used to reduce heavy metal oxides to metals Used as a rocket fuel in space research Used in fuel cells for generating electrical energy, as it doesn’t produce any pollution and releases greater energy per unit mass than any other fuels 7

Water - H20:

Water - H 2 0 Water plays a key role in the biosphere It is a crucial compound for the survival of all life forms A major part of all living organism is made up of water Human body has about 65% and some plants have as much as 95% of water The distribution of water over the earth’s surface is not uniform Estimated world water supply Source % of total water Oceans 97.33 Saline lakes and inland areas 0.008 Polar ice and glaciers 2.04 Ground water 0.61 Lakes 0.009 Soil moisture 0.005 Atmospheric water vapour 0.001 Rivers 0.0001 8

Properties of Water:

Properties of Water Colourless and tasteless liquid Molecular mass – 18 g/mol High freezing point – 273K High boiling point – 373K High heat of vaporisation – 40.66 kJ/mol High heat of fusion – 6.01 kJ/mol Compare to other liquids, water has higher specific heat, thermal conductivity, surface tension, dipole movement, dielectric constant etc. Amphoteric in nature, acts as acid as well as a base Dissolves many ionic compounds and some covalent and ionic compounds are hydrolysed in water 9

Structure of Water:

Structure of Water 10

Structure of Ice:

Structure of Ice 11

Hard and Soft Water:

Hard and Soft Water Hard Water Soft Water Soluble salts of calcium and magnesium are present in the water Soluble salts of calcium and magnesium are absent in the water It does not give lather with soap It gives lather with soap It forms scum when reacting with soap It doesn’t form scum when reacting with soap 12

Hardness of Water:

Hardness of Water The hardness of water is of two types:- Temporary Hardness Due to the presence of magnesium and calcium hydrogen carbonate It can be removed by boiling or by Clark’s method, adding calculated amount of lime to hard water which precipitates out calcium carbonate and magnesium hydroxide Permanent hardness Due to the presence of soluble salts of magnesium and calcium in the form of chlorides and sulphates in water It can be removed by:- Treating the water with washing soda Calgon’s method, adding sodium hexametaphosphate(Na 6 P 6 O 18 ) commercially called as calgon to hard water Ion-exchange method Synthetic resin method 13

Hydrogen Peroxide - H2O2:

Hydrogen Peroxide - H 2 O 2 It is an important chemical used in pollution control treatment of domestic and industrial effluents 14

Properties of H2O2 :

Properties of H 2 O 2 It is almost a colourless (very pale blue) liquid It is miscible with water and forms a hydrate A 30% solution of is marketed as ‘100 volume’, which means that one millilitre of 30% of will give 100 ml of oxygen at STP It acts as oxidising and reducing agent in acidic and alkaline media   15

Structure of H2O2:

Structure of H 2 O 2 H 2 O 2 structure in gas phase H 2 O 2 structure in solid phase at 110K 16

Storage of H2O2:

Storage of H 2 O 2 H 2 O 2 decomposes slowly on exposure to light. The reaction - In the presence of metal surface, the above reaction is catalysed Therefore, it is 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   17

Uses of H2O2:

Uses of H 2 O 2 It is used as hair bleach and as a mild disinfectant It is used to manufacture chemicals like sodium perborate and per-carbonate, which used in high quality detergents It is used as an antiseptic for washing wounds, teeth and ears under the name perhydrol It is used in the synthesis of hydroquinone, certain food products like tartaric acid It is used in the industries as bleaching agent for paper, pulp, leather, oils, fats etc. It is used to make pharmaceuticals It is used for restoring the colour of lead paintings It is used for restoring the colour of lead paintings Nowadays it is used in environment chemistry like pollution control of domestic and industrial effluents, oxidation of cyanides, restoration of aerobic conditions to sewage wastes etc. 18

Heavy Water – d2o:

Heavy Water – d 2 o It is 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 Its molecular mass is of 20 g/mol Its melting point is 276.8 K and boiling point is 374.4 K Its density is 1.1059 g/cm 3 It is used for the preparation of other deuterium compounds, for example :-   19

Dihydrogen as a fuel:

Dihydrogen as a fuel Dihydrogen releases large quantities of heat on combustion From the table below it is clear that dihydrogen releases more energy than petrol Also pollutants in combustion of dihydrogen will be less than petrol The only pollutant of dihydrogen is dinitrogen Tanks of metal alloy are used for storage of dihydrogen in small quantities Nowadays, dihydrogen is used in fuel cells for generation of electric power Energy released on combustion in kJ Dihydrogen (in gaseous state) Dihydrogen (in liquid) LPG CH 4 gas Octane (in liquid state) Per mole 286 285 2220 880 5511 Per gram 143 142 50 53 47 Per litre 12 9968 25590 35 34005 20

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