Chemistry

Hydrogen

What do you understand by word “Hydrogen” ? Session opener What do you understand by word “Hydrogen” ? Hydrogen in Greek means Water producer

Session Objectives

Session objective Position of Hydrogen in periodic table Isotopes of hydrogen Methods of preparation, properties and uses of dihydrogen. Hydrides Water — physical and chemical properties Hardness of water and methods to remove it. Heavy water

Session objective 9. preparation, properties and uses of hydrogen peroxide. 10.Hydrogen economy 11.Uses of hydrogen as a fuel 12.Hydrazone

Session opener Hydrogen in Greek means “water producer”

Position of Hydrogen in Periodic Table lightest element known having atomic number 1. Dihydrogen The position of hydrogen is anomalous in periodic table Alkali metals Halogens In modern periodic table it is located in first group.

Resemblance with alkali metals 1. Electronic configuration 2. Electropositive character H+, Na+, K+ etc. 3. Oxidation state: +1

Resemblance with halogens 1. Electronic configuration: Both contain one electron less than the nearest noble gas configuration 2. Non-metallic character: Typical non-metals. 3. Atomicity: Diatomic molecules.

4. Formation of similar types of compounds i. Halides: CCl4, SiCl4, GeCl4 ii. Hydrides: CH4, SiH4, GeH4 5. Oxidation state: –1

Isotopes of hydrogen

Methods for commercial production of dihydrogen 1. Electrolysis of water 2. By partial oxidation of hydrocarbons

Methods for commercial production of dihydrogen 3. Water gas shift reaction

By Lane process (1) Oxidation stage (2) Reduction stage

Bosch process CO2 dissolves + H2 is collected

Laboratory preparation of hydrogen Zn + dil H2SO4 ZnSO4 + 2H2O + SO2 Chemical properties:- Not very reactive due to high bond dissociation energy (435.88 kJ mol-1 at 298.2 K)

Ask yourself? Can we use concentrated sulphuric acid and pure zinc in the preparation of dihydrogen? (a) Conc. H2SO4 cannot be used because it acts as oxidizing agent also and gets reduced to SO2. (b) Pure Zn is not used because it is non-porous and reaction will be slow. The impurities in Zn help in constitute of electrochemical couple and speed up reaction.

Chemical properties (i) Combustion:- It burns with pale blue flame 2H2 (g) + O2 (g) 2H2O(l) (ii) Reaction with nitrogen 3H2 (g) + N2 (g) 2NH3 (g) (iii) Reaction with oxygen

Chemical properties (iv) Reaction with metals Reactive metals like Na, K, Ca, Li Metals like Pt, Pd, Ni form interstitial hydrides by absorbing large volume of hydrogen. Such hydrogen is called ‘occluded hydrogen’ (v) Reaction with metal oxides:- Hydrogen reduces oxides of less active metals to corresponding metal

Ortho and para hydrogens At room temp. 75% 25% stability less stable more stable Different physical properties Similar chemical properties.

Atomic hydrogen Highly reactive. Half life period is 0.3 sec. Nascent hydrogen The hydrogen produced in contact with the substance to be reduced is known as ‘nascent hydrogen’. It is very reactive form of hydrogen Better reducing agent than ordinary dehydrogen.

Structure of water Gaseous state Solid state

Structure of ice

Hard water Contains dissolved salts of bicarbonates, sulphates and chlorides of calcium and magnesium. Hard water does not produce lather with soap solution. Soft water Soft water is free from bicarbonates, sulphates and chlorides of calcium and magnisum. It produce lather with soap solution easily. e.g., distilled water, rain water

Types of hardness The hardness of water is of two types (i)Temporary hardness • due to presence of soluble bicarbonates of calcium and magnesium. • can be removed by simple boiling. (ii)Permanent hardness • due to presence of chlorides and sulphates of calcium and magnesium. • requires treatment of water to remove this type hardness.

Do you know? Temporary hardness is also called carbonate hardness Permanent hardness is also called non-carbonate hardness

Softening of water The process of removal of Ca2+ and Mg2+ ions from water is called softening of water. Removal of temporary hardness:- (M = Ca or Mg) Clark’s method or calcium hydroxide method

Removal of permanent hardness (i) By washing soda (Na2CO3.10H2O) treatment

Removal of permanent hardness ii)By using inorganic cation exchanger (permutit method or Zeolite method): The zeolite can be regenerated by treatment with sodium chloride solution.

Removal of permanent hardness (iii) By organic ion exchanger: Cation exchanger

Anion exchanger

Hydrogen peroxide Methods of preparation 2. From Barium peroxide Barium sulphate is filtered off leaving behind H2O2.

3. By electrolysis of 50% H2SO4 At cathode At Anode H2O2 distills first leaving behind the H2SO4 which is recycled.

4. By auto oxidation of 2-ethylanthraquinol The H2O2 obtained by this method is further concentrated by distillation under reduced pressure.

Oxidising properties

Oxidising properties

Reducing properties

Reducing properties

Acidic properties It reacts with alkalies and decomposes carbonates. Uses of hydrogen peroxide 1. For bleaching silk, wool, hair and leather 2. As rocket fuel 3. Dilute solution is sold in name ‘perhydrol’

Do you know? H2O2 is stored in the bottles lined with wax because… The rough glass surface causes the decomposition of hydrogen peroxide.

Volume strength of hydrogen peroxide (solved example 1) Calculate the percentage strength of a 10 volume H2O2 solution. 10 volume hydrogen peroxide means that 1 ml of such a solution of hydrogen peroxide on heating will produce 10 ml of oxygen at N.T.P. 2(2 + 32) gm 22.4L at N.T.P. = 68 gm or 22400 cm3 at N.T.P.

Solution But 10 ml of O2 at N.T.P. are produced from 1 ml of 10 volume H2O2 solution. = 0.03035 gm

Volume strength of hydrogen peroxide (solved example 2) Calculate the normality of 30 volume of H2O solution: 2(2 + 32) gm 22.4L = 68 gm 22.4 L of O2 is produced from = 68 gm of H2O2 68 parts by weight 32 parts by weight

Solution 32 parts by weight of oxygen is obtained from = 68 parts by weight of H2O2

Structure of hydrogen peroxide

Illustrative example Calculate the normality of 30 volume of H2O solution: Solution: 2(2 + 32) gm 22.4 L = 68 gm 22.4 L of O2 is produced from = 68 gm of H2O2 = 91.07 gm/mL

solution 68 parts by weight 32 parts by weight 32 parts by weight of oxygen is obtained from = 68 parts by weight of H2O2 parts by weight of oxygen is obtained from =

Heavy Water (D2O) Was discovered by Urey in 1932. Ordinary water contains one part of heavy water in 600 parts of it. Used as moderator in nuclear reactions. Used as tracer in study of mechanism of physiological process. Used in preparation of deuterium compounds.

Hydrogen economy (Hydrogen as fuel) With advancement of science and technology we realise in order to make our lives comfortable fossil fuels are depleating at an alarming rate and will be exahausted soon. The electricity cannot be stored to run automobiles. It is not possible to store and transport nuclear energy. Hydrogen is another alternative source of energy and hence called as ‘hydrogen economy’. Hydrogen has some advantages as fuel

Hydrogen economy (Hydrogen as fuel) Available in abundance in combined form as water. On combustion produces H2O. Hence pollution free. H2-O2 fuel cell give more power. Excellent reducing agent. Therefore can be used as substitute of carbon in reduction for processes in industry.

Obstacles in hydrogen economy Transportation: Hydrogen gas is explosive and hence it is difficult to store and transport. Formation of hydrogen from H2O: The cheaper production of the hydrogen is basic requirement of hydrogen economy which is not possible now. The main aim and advantage of hydrogen economy is to transmit energy in four of hydrogen.

Thank you