Session objective 1.Position of Hydrogen in periodic table 2.Isotopes of hydrogen 3.Methods of preparation, properties and uses of dihydrogen. 4.Hydrides 5.Water — physical and chemical properties 6.Hardness of water and methods to remove it. 7.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 In modern periodic table it is located in first group. Alkali metals Halogens lightest element known having atomic number 1. Dihydrogen The position of hydrogen is anomalous in periodic table
Resemblance with alkali metals 1. Electronic configuration H +, Na +, K + etc. 3. Oxidation state: +1 2. Electropositive character
Resemblance with halogens Both contain one electron less than the nearest noble gas configuration Typical non-metals. Diatomic molecules. 1. Electronic configuration: 2. Non-metallic character: 3. Atomicity:
4. Formation of similar types of compounds i. Halides: CCl 4, SiCl 4, GeCl 4 ii. Hydrides: CH 4, SiH 4, GeH 4 5. Oxidation state: –1
Methods for commercial production of dihydrogen 2. By partial oxidation of hydrocarbons 1. Electrolysis of water
Methods for commercial production of dihydrogen 3. Water gas shift reaction
By Lane process (2) Reduction stage (1) Oxidation stage
Bosch process CO 2 dissolves + H 2 is collected
Laboratory preparation of hydrogen Zn + dil H 2 SO 4 ZnSO 4 + 2H 2 O + SO 2 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. H 2 SO 4 cannot be used because it acts as oxidizing agent also and gets reduced to SO 2. (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 2H 2 (g) + O 2 (g) 2H 2 O(l) 3H 2 (g) + N 2 (g) 2NH 3 (g) (ii) Reaction with nitrogen (iii) Reaction with oxygen
Chemical properties 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’ (iv)Reaction with metals Hydrogen reduces oxides of less active metals to corresponding metal (v)Reaction with metal oxides:-
Ortho and para hydrogens At room temp. 75%25% stability more stable less stable Different physical properties Similar chemical properties.
Atomic hydrogen Highly reactive. Half life period is 0.3 sec. 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. Nascent hydrogen
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 is free from bicarbonates, sulphates and chlorides of calcium and magnisum. It produce lather with soap solution easily. Soft water e.g., distilled water, rain water
Types of hardness due to presence of soluble bicarbonates of calcium and magnesium. can be removed by simple boiling. The hardness of water is of two types (i)Temporary hardness due to presence of chlorides and sulphates of calcium and magnesium. requires treatment of water to remove this type hardness. (ii)Permanent 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 Ca 2+ and Mg 2+ ions from water is called softening of water. (M = Ca or Mg) Removal of temporary hardness:- Clark’s method or calcium hydroxide method
Removal of permanent hardness (i) By washing soda (Na 2 CO 3.10H 2 O) 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
Acidic properties It reacts with alkalies and decomposes carbonates. 1.For bleaching silk, wool, hair and leather 2.As rocket fuel 3.Dilute solution is sold in name ‘perhydrol’ Uses of hydrogen peroxide
Do you know? H 2 O 2 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 H 2 O 2 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 cm 3 at N.T.P.
Solution But 10 ml of O 2 at N.T.P. are produced from 1 ml of 10 volume H 2 O 2 solution. = 0.03035 gm
Volume strength of hydrogen peroxide (solved example 2) Calculate the normality of 30 volume of H 2 O solution: 2(2 + 32) gm 22.4L = 68 gm 22.4 L of O 2 is produced from = 68 gm of H 2 O 2 68 parts by weight32 parts by weight
Solution 32 parts by weight of oxygen is obtained from = 68 parts by weight of H 2 O 2
Illustrative example Calculate the normality of 30 volume of H 2 O solution: Solution: 2(2 + 32) gm 22.4 L = 68 gm 22.4 L of O 2 is produced from = 68 gm of H 2 O 2 = 91.07 gm/mL
solution 68 parts by weight32 parts by weight 32 parts by weight of oxygen is obtained from = 68 parts by weight of H 2 O 2 parts by weight of oxygen is obtained from =
Heavy Water (D 2 O) 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 H 2 O. Hence pollution free. H 2 -O 2 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 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. Transportation: Hydrogen gas is explosive and hence it is difficult to store and transport. Formation of hydrogen from H 2 O: