Hydrogen and Its Compounds

INTRODUCTION Hydrogen is the lightest element and also the lightest gas in the periodic table. It is the lightest non-metal. It is the simplest element in periodic table having only 1e –, 1p & no neutron. Electronic configuration of H is 1s1 Number of e– = 1 Number of orbital = 1 Number of shells = 1 Number of subshell =1 It is discovered by Henry Cavendish & it was called inflammable element. The name hydrogen was given by Lavoisier HYDROGEN Hydro (Water) Gene (Producer) or generator means according to Lavoisier the gas which produce water on burning with oxygen. H2 + 1 O2  H 2O 2 Order of Abundance of H Hydrogen is the most abundant element in the universe (70% of the total mass of the universe.) Order of abundance of H Universe > Sun atm > Earth The planet Jupiter & Saturn consist mainly of H2. Similarly about half the mass of the sun & some other stars is made up of hydrogen. In Sun's atmosphere & in universe, It is found in atomic form. While in earth it is generally found in molecular form. At Sun, the stratosphere is made up of H (atomic hydrogen) & they undergoes fusion & converted into He nuclei & this reaction is exothermic so lot of amount of energy is liberated. It is the ninth element on earth in order of abundance. Earth does not posses enough gravitational force to retain live hydrogen molecule i.e. why it is not found in earth atmosphere in atomic form. Hydrogen is the most reactive elements in atomic form but it is less reactive in molecular form because of very high bond dissociation energy due to 1s -1s overlapping. POSITION OF H2 IN PERIODIC TABLE Hydrogen is the first element of Periodic table but still it could not be assigned a proper position either in Mendeleef periodic table or in Modern periodic table because of following reasons. It may kept in 1st/IA or 17th/VIIA group due to following reason. Resembles with 1st / IA Alkali metals. (i)  ELECTRONIC CONFIGURATION : Like alkali metals hydrogen also has only one electron in outer most shell. H = 1s1 K = 4s1  Li = 2s1  Na = 3s1 Rb = 5s1 ns1 HYDROGEN AND ITS COMPOUNDS (ii) (iii) (iv) ELECTROPOSITIVE CHARACTERS : Like alkali metals hydrogen also have the tendency to loose one electron to form cation. Ex. Na  Na+ + e– H  H+ + e– (Proton) OXIDATION NUMBERS : Like alkali metals hydrogen can also exhibit the oxidation number of +1 in most of its compound. Ex. Na+Cl– K+Cl H+ Cl– = +1 REACTION WITH ELECTRONEGATIVE ELEMENTS (NON-METALS) : Like alkali metals H also reacts with Oxygen, Sulphur, Halogens to form oxides, sulphides and halides respectively. gives O   H2O, like Na2O, K2O gives S    H2S, like Na2S, K2S gives with halogen    (v) HX, like NaX, KX LIBERATIONAT CATHODE 2Na+ Cl 2Na electrolysis    + Cl2 (liberated at cathode)(liberated at anode) 2H+ (vi) Cl– electrolysis    (H2 + Cl2) like alkali metals H also get liberated at cathode on electrolysis. REDUCING NATURE : Like alkali metals H2 also have reducing nature. CuO + H2 Cu + H2O Due to resembling of these properties with alkali metals H can be placed in IA/group/alkali metals group. Resembles with halogen/ VIIA/17th (i) ELECTRONIC CONFIGURATION Electronic configuration of halogen H 1s1  ns2np5 both these requires one electron to attain the stable configuration of their nearest inert gas.  2 e less than H 1s1  1  He (1s )  6 e less than F 2p5  1  Ne (2p )  6 e less than Cl  3p5  1  Ar (3p ) (ii) ELECTRONEGATIVE CHARACTER : Both halogen & Hydrogen has the tendency to gain one e–. F + e– F— H + e– H– i.e. why both will act as electronegative species. (iii) IONIZATION POTENTIAL : Ionization potential of hydrogen is almost similar to halogen. (iv) OXIDATION NUMBER : Both halogen & hydrogen can exhibit –1 oxidation number. Hydrogen in metal hydride shows –1 oxidation state. NaH Na+ + H– NaCl Na+ + Cl– (v) DIATOMIC MOLECULE : Both halogen & hydrogen have the tendency to exist as diatomic molecule. Ex. F2, Cl2 Br2, I2 & H2. (vi) LIBERATION AT ANODE : Whenever Alkali metals halides & hydrides undergoes electrolysis, both halogen and hydrogen will liberate at anode. 2Na+ Cl– 2Na + Cl2 (anode) 2Na+ H– 2Na + H2 (anode) (vii) REACTION WITH HIGHLY ELECTROPOSITIVE METALS : Hydrogen reacts with highly electropositive element (i.e. s-block elements) & forms their hydrides like their halides. 2Na + H2 2NaH 2Na + Cl2 2NaCl This reaction shows oxidising character of hydrogen. (viii) FORMATION OF COVALENT COMPOUND : Both Hydrogen & halogen on reaction with non metals to form covalent compounds like. CH4, NH3, H2O CCl4, NCl3, Cl2O Conclusion : The position of hydrogen is still in controversy & no proper position is assigned to H in periodic table i.e. why it is also called notorious or rogue elements. ISOTOPES OF HYDROGEN There are 3 isotopes of H2 Symbol Protium or Deuterium/ ordinary hydrogen Heavy hydrogen 1 H1 H2 1 H2/1D2 D2 Tritium 1 H3/1T3 T2 Property Protium or ordinary hydrogen Deuterium or heavy hydrogen Atomic number Mass number Exact atomic mass 1 1 1.008123 1 2 2.0142 1 3 3.0170 Symbol 1 1H 2 1 3 1 Molecular formula No. of protons in the nucleus No. of neutrons in the nucelus No. of electron Electronic configu. Relative abundance Stability H2 D2 T2 1 1 1 Nil 1 1s1 99.984% Stable 1 1 1s1 0.016% Stable 2 1 1s1 10–15 % Unstable(Radioactive) H or 21 D Tritium H or 31 T HYDROGEN AND ITS COMPOUNDS Properties H2 D2 T2 M.P. – 2590C – 254.30C – 252.40C B.P. – 252.60C – 249.30C – 248.00C Bond length (H– H) 74 pm 74 pm 74 pm Bond energy (H—H) 436.0 KJ mol–1 443.3 KJ mol–1 446.9 KJ mol–1 Heat of fusion & vaporisation Minimum H Nascent hydrogen > Molecular hydrogen (c) BASED ON NUCLEAR SPIN (NUCLEAR ISOMERS) (i) Ortho hydrogen – The molecular form of hydrogen having same spin of proton is called ortho hydrogen. HYDROGEN AND ITS COMPOUNDS (ii) Para hydrogen – The molecular form of hydrogen having opposite spin of proton is called para hydrgen. In ortho hydrogen spin of proton is same, so they will repel each other & because of this repulsion, internal energy of ortho hydrogen increases. So ortho hydrogen has more internal energy. Stability of ortho & para hydrogen Stability of ortho & para hydrogen depends upon temperature condition. At low temp : para hydrogen is more stable than ortho hydrogen while at high temp ortho hydrogen is more stable than para hydrogen. At 25°C At –253°C/20K Ortho 75% 0 Para 25% 100% KEY POINTS (i) (ii) We can obtain 100% pure para hydrogen at low temp but can't ortho because at high temp parahydrogen will dissociate into atomic hydrogen. Ortho & Para hydrogen differs only in physical properties but have same chemical properites. METHOD OF PREPARATION (i) FROM ACIDS : The metal which are placed about H2 in electrochemical series react with dil acids they liberate H2. Ex. Fe + H2SO4 FeSO4 + H2 (dil) Cu + H2SO4 × (No reaction) Lab preparation : When impure Zn reacts with dil H2SO4 it forms H2 Zn + H2SO4 ZnSO4 + H2 (impure) (dil) Ex. Why we use impure Zn. Ans. Because the rate of reaction with pure Zn is very slow. (2) BY ALKALIES : Only (Be, Zn, Al, Sn, Pb, Si) (Amphoteric metal) react with boiling NaOH or KOH they evolve H2. Zn + 2NaOH Na2ZnO2 + H2 (sodium zincate) 2Al + 2NaOH + 2H2O NaAlO2 + 3H2 (sodium meta aluminat e) Sn + 2NaOH + H2O Na2SnO3 + 2H2 (sodium stannate) Pb + 2NaOH + H2O Na2PbO3 + 2H2 (sodium plumbate) Si + 2NaOH + H2O Na2SiO3 + 2H2 (sodium silicate) Be + 2NaOH Na2BeO2 + H2 (sodium beryliate) (3) FROM WATER All the metals which are placed above than H2 when react with water the evolve H2. Zn + H2O ZnO + H2 Three type of water is used (i) Cold water : The temperature of cold water is 7 to 25°C this water is used for highly reactive metals. Such as Li, K, Ba, Sr, Ca, Na, means alkali metals of alkaline earth metals. The reaction with alkali metals are vigorous to minimum the rate of reaction these metals are used in the form of amalgam. 2Na(Hg) + H2O 2NaOH + H2 (ii) Hot water : The temperature of hot water is 25°C to 90°C. This water is used for reactive metals, such as Mg, Al, Mn, Zn, Cr. (iii) Steam : The temperature of steam is more than 100°C. This form of water is used for very less reactive metals like Fe, Cd, Co, Ni, Sn, Pb. Condition for best yield of H2 (4) (i) Cold water With highly reactive metals. (ii) Hot water With reactive metals (iii) Steam With less reactive metals. ON IONIC HYDRIDE Whenever ionic hydride reacts with water then form H2. CaH2 + 2H2O Ca(OH)2 + H2 (Hydrolith) NaBH4 + H2O NaBO2 + 4H2 METHOD TO PREPARE PURE HYDROGEN 1. ELECTROLYSIS OF WATER : To prepare pure hydrogen we use impure water (i.e. having 15-20% solution of alkali or acid) 4H2O l 4H+ + 4OH– at cathode 4H+ + 4e– 2H2 at anode 4OH– 2H2O + O2 + 4e– The SO4–2 or K+ ion present in acid or alkali does not move towards anode or cathode as their discharge potential is higher than of OH– ions or H+ ions respectively. 2. BY REACTION OF MAGNESIUM WITH DIL. H2SO4 Mg + H2SO4 MgSO4 + H2 3. B REACTION OF NAH WITH WATER NaH + H2O NaOH + H2 4. UYENO METHOD : This method is used for military purpose 2Al + 2KOH + 2H2O 2KAlO2 + 3H2 (Potassium meta aluminate) Because by this reaction we can prepare H2 in a rapid manner. HYDROGEN AND ITS COMPOUNDS COMMERCIAL OR INDUSTRIAL METHOD TO PREPARE H2 (i) LANE PROCESS : Steam is passes over hot iron it converts into Fe3O4 & H2. 3Fe + 4H2O Fe3O4 + 4H2 Iron is regenerated by reducing Fe3O4 into Fe by water gas (CO + H2) 2Fe3O4 + 4CO + 4H2 6Fe + 4CO2 + 4H2O Fe3O4 + 2CO + 2H2 3Fe + 2CO2 + 2H2O This process is a continuous process. (ii) BOSCH PROCESS : In this process initially steam is passed over red hot coke then water gas is formed. C + H2O CO + H2 Then water gas is mixed with more stem in presence of Fe2O3/Cr2O3 then CO will convert into O2 & we can obtain more H2. CO + H2 + H2O CO2 + 2H2 (iii) FROM NATURALGAS CnH2n+2 + nH2O nCO + (2n + 1)H2 PHYSICAL PROPERTIES OF HYDROGEN (i) (ii) (iii) (iv) Hydrogen is a lightest, colourless, odourless and tasteless gas. It is sparingly soluble in water. It is inflammable and less reactive gas. Its f.p. (– 259.20C) and b.p. (–2520C) are very low indicating less intermolecular attraction. Due to low f.p. liquid hydrogen is used as a cryogenic fluid (to produce low temperature). H—H bond energy [ 104 Kcal mol–1] and 436 KJ/m H – H bond length [ 74 pm] so H2 is less reactive and require high temp for reaction. CHEMICAL PROPERTIES OF H2 (i) (ii) (iii) H2 is neutral in nature i.e. why it does not react with acids & bases. LESS REACTIVE : Hydrogen is very less reactive in nature because of very high bond dissociation energy. COMBUSTIBLE NATURE : H2 is highly combustible in nature & it burns with oxygen or air with pale blue flame to give water. H2 + 1 O H2O 2 2 (iv) REACTION WITH HIGHLY ELECTROPOSITIVE METALS IA & IIA group elements are called highly electropositive metal. Whenever H reacts with these metals they form ionic hydrides. 2Na + H2 2NaH CO + H2 CaH2 (vi) REACTION WITH NON-METAL (a) Reaction with halogen H2 + X2 2HX  [F2, Cl2, Br2, I2] order of reactivity of halogen with hydrogen F2 > Cl2 > Br2 > I2 (b) Reaction with sulphur H2 + S H2S (c) With nitrogen – (Haber process) 6 83K  2NH3 N2 + 3H2  Fe, Mo, 2 00 atm (vi) (vii) REDUCINGNATURE CuO + H2 Cu + H2O REACTION WITH CARBON MONO OXIDE ZnO / Cr O 2 3  CH OH (Methanol) 2H2 + CO  3 37 3K (viii) HYDROGENATION OF UNSATURATED HYDROCARBON C2H2 + 2H2 C2H6 Ni / Pb / Pt CH C2H4 + H2  2 6 4 73 K When unsaturated hydrocarbon having C = C or C C reacts with hydrogens in the presence of Ni/Pd/Pt forms saturated hydrocarbons. KEY POINTS Hydrogenation of vegetable oil. Vegetable oils are also called polyunsaturated oils because they contain many C = C bond. When these oil are exposed to air for a long time then double bond will get oxidized and the oil becomes. Rancid (having fowl. smell or unpleasant test) in nature. So to avoid this vegetable oil are converted into edible fats (Vanaspati Ghee) Ni  edible fats solid Vegetable oils + H2   (liquid) This whole process is known as hydrogenation or hardening of oil. USES OF HYDROGEN 1. 2. 3. 4. Hydrogenation of vegetable oil to form solid fats i.e. vanaspati ghee. In liquid form as a rocket fuel. (Liquid H2 + Liquid O2) In a air ship of balloons as a mixture of Hydrogen & Helium [15% H2 + 85% He] Formation of different compounds. Like NH3, (Haber process) alkane, alcohol and other hydrocarbon Ex. Sol. Write the names of isotopes of hydrogen. What is the mass ratio of these isotopes ? The various, isotopes of hydrogen are : 1 1H (Protium) ; 2 1H or D(Deuterium) ; 13 H or T(Tritium) The mass ratio of 11H : 12 H : 13 H is 1 : 2 : 3 Ex. Sol. Why does hydrogen occur in a diatomic form rather than in a monoatomic form under normal conditions ? Hydrogen atom has only one electron and thus, to achieve stable inert gas configuration of helium, it shares its single electron with electron of other hydrogen atom to form a stable diatomic molecule. The stability of H2 is further confirmed by the fact, that formation of one mole of gaseous H2 molecules results in the release of 435.8 kJ of energy H(g) + H(g)  H2(g) ; H = – 435.8 kJ mol–1 Ex. Sol. Which of the following can adsorb largest volume of hydrogen gas? (1) Finely divided platinum (2) Finely divided nickel (3) Colloidal palladium (4) Colloidal platinum Order of adsorption of H2(occlusion) is : Colloidal Palladium > Palladium > Platinum > Gold > Nickel. Ans. (3) HYDROGEN AND ITS COMPOUNDS Ex. Describe the bulk preparation of hydrogen by electrolytic method. What is the role of an electrolyte in this process Sol.: The electrolyte (15–20% NaOH solution) increases conductivity of water. Cathode (iron) : Reduction of water occurs. 2H2O + 2e–  2H2 + 2OH– Anode (nickel coated iron) : Oxidation of OH– occurs. 2OH–  H2O + 1/2 O2 + 2e– Ex. Complete the following reactions :  (ii) CO(g) + H2(g)   (i) H2(g) + MmOn(s)  Catalyst  (iii) C3H8(g) + 3H2O(g)  Catalyst Ans.  (iv) Zn(s) + NaOH(aq)   (i) nH2(g) + MmOn(s)  mM(s) + nH2O()  (ii) CO(g) + 2H2(g)  CH3OH() (methanol) Catalyst Ni (iii) C3H8(g) + 3H2O(g)  3CO(g) + 7H2(g) 1270K heat (iv) Zn(s) + 2NaOH(aq)   Na2ZnO2(aq) + H2(g) Ex. Sol. Can conc. H2SO4 be used for drying H2 gas ? Justify. Conc. H2SO4 cannot be used for drying H2 gas because H2SO4 does absorb moisture from moist H2, but the process is highly exothermic. The heat so produced causes hydrogen to catch fire because of its inflammable nature. Ex. Can dihydrogen act as oxidising agent ? If so give chemical reactions to support the statement. Sol. Dihydrogen can act as oxidising agent when it forms metal hydrides. 2Li + H2  2LiH HYDRIDES The compounds of hydrogen with different elements are called hydrides. These are of three types : (1) IONIC/SALT LIKE/SALINE HYDRIDES Compounds of hydrogen with s-block elements except berylium & magnesium are called ionic hydrides. LiH, NaH, KH, RbH, CsH, CaH2, SrH2, BaH2 BeH2, MgH2 are covalent polymeric hydride. • Structure of these hydrides are similar to rock salt, so they are also called salt like/saline hydrides. • Down the group sizeLattice energystabilityMelting pointBoiling point • On electrolysis of these hydrides, hydrogen is liberated at anode. • On reaction with water these hydrides will form hydrogen NaH + H2O NaOH + H2 • These hydrides forms complex hydrides which are very good reducing agents. 4LiH + AlCl3 LiAlH4 + 3LiCl NaBH4 Sodium borohydride LiAlH4 Lithium aluminium hydride. (2) METTALIC / INTERSTITIALHYDRIDES They are the compounds of d & f-block elements. • • • (3) • • In these hydrides hydrogen occupies interstitial sites present in metallic lattice, so they are called interstitial hydrides. Properties of these hydrides are similar to parent metals, so they are also known as metallic hydrides. These hydrides are non. stoichiometric in nature (i.e. having variable composition) ZrHx (x = 1.3 – 1.75) TiHx (x = 1.8 – 2) Metals of group 7,8,9 donot form any hydrides so this particular part of periodic table is known as hydride gap. COVALENT/MOLECULES HYDRIDES They are the compounds of hydrogen with p-block elements CH4, NH3, H2O, HF, etc. These hydrides exist as molecules, so they are also known as molecular hydrides. There hydrides are nonconductor of electricity. Nomenclature – element + Suffix (ane) PH3 Phosphane NH3 Azane H2O Oxidane These hydrides are again divides into 3 categories. (a) Electron deficient hydrides : • They are the hydrides of group 13 elements. BH3, AlH3, GaH3 – In these hydrides central element does not have complete octet. i.e. why they are called electron deficient compounds. (b) Electron precise hydrides – They are the hydrides of group 14 element. Ex. CH4, SiH4, GeH4 In these type of hydrides central elements has 8e– in their outer most shell. (c) Electron rich hydrides : These are the hydrides of group 15, 16, 17 Ex. etc. In these hydrides lone pair are present on central dement which can be given to others. So they are called electron rich hydrides. Ex. Sol. What characteristics do you expect from electron deficient hydrides with respect to their structure and chemical reactivity ? Electron deficient hydrides do not have sufficient number of electrons to form normal covalent bonds. They generally exist in polymeric forms such as B2H6, B4H10, (AIH3)n, etc. Due to deficiency of electrons, these hydrides act as Lewis acids and thus, form complex entities with Lewis bases such as : NH3, H– ions, etc.  B2H6 + 2 N H3  [BH2(NH3)2]+[BH4]– B2H6 + 2NaH  2Na+[BH4]– (sodium borohydride) Ex. Sol. Do you expect the carbon hydride of the type (CnH2n+2) to act as Lewis acid or base ? Justify your answer. Carbon hydride of the type (CnH2n+2) are electronprecise hydrides. In other words, they have exact numbers of electrons required to form covalent bonds. Therefore, they do not have tendency to either gain or lose electrons and hence, they do not act as Lewis acids or Lewis bases. HYDROGEN AND ITS COMPOUNDS Ex. Sol. Arrange the following : (i) CaH2, BeH2 and TiH2 in order of increasing electrical conductance. (ii) LiH, NaH and CsH in order of increasing ionic character (iii) H–H, D–D and F–F in order of increasing bond dissociation enthalpy. (iv) NaH, MgH2 and H2O in order of increasing reducing property. (i) BeH2 is a covalent hydride, therefore, it does not conduct electricity at all. CaH2 conducts electricity in the fused state while TiH2 conducts electricity at room temperature. Thus, the order of increasing electrical conductance is : BeH2 < CaH2 < TiH2. (ii) Electronegativity decreases down the group from Li to Cs, therefore, the ionic character of their hydrides also increases in the same order, i.e., LiH, < NaOH < CsH. (iii) F – F bond dissociation enthalpy is the minimum. This is due to high concentration of electron density around each F atom in the form of 3 lone pairs which cause significant repulsive interactions. The bond enthalpy of D– D bond is slightly higher than that of H–H bond. It is due to marginally smaller size of D. Thus, the bond dissociation enthalpy increases in the order : F–F < H–H < D–D. (iv) Ionic hydrides are powerful reducing agents. Both MgH2 and H2O are covalent hydrides but the bond dissociation of O–H bonds in H2O is much higher than that of Mg–H bond in MgH2. Therefore, the reducing character increases in the order : H2O < MgH2 < NaH. Ex. Sol. How do you expect the metallic hydrides to be useful hydrogen storage ? Explain. In some of the transition metal hydrides, hydrogen is absorbed as H atoms. Due to the inclusion of H-atoms, the metal lattice expands and thus becomes less stable. Therefore, when such metallic hydride is heated, it decomposes to release hydrogen gas and very finely divided metal. The hydrogen evolved in this manner can be used as a fuel. Thus, transition metals or their alloys can act as sponge and can be used to store and transport hydrogen to be used as a fuel. Ex. Ans. Explain the meaning of term hydride gap. Elements of group 7, 8, 9 of d-block do not form hydrides at all. This inability of metals of group 7, 8, 9 of periodic table to form hydrides is referred to as hydride gap of d-block. Ex. Explain the following : (a) Water is excellent solvent for ionic compounds. (b) Lakes freeze from top to bottom. (a) Water has a high dielectric constant (78.39) due to the polar character of its molecule. Water is an excellent solvent for many ionic as well as covalent compounds. Dissolution of ionic compounds takes place because of ion-dipole interactions. Dissolution of molecular compounds such as alcohols, amides, urea, sugar, glucose, honey, etc., in water takes place because of the tendency of these substances to form hydrogen bonds with water molecules. (b) This is due to the fact that the frozen water does not sink to the bottom but keeps floating at the surface due to its lesser density. This provides thermal insulation to the water below it. The lesser density of ice can be attributed to open cage-like structure on account of hydrogen bonding. Sol. PROPERTIES OF PURE WATER (a) Physical properties WATER (H2O ) (i) Pure water is colourless, tasteless and odourless. It gives bluish tinge in thick layers. (ii) It freezes at 0°C and boils at 100°C. (iii) Its maximum density is 1.00 at 4°C. (iv) It is a polar molecule and has V-shaped structure. The bond angle is 104.5°. (v) It has a high dielectric constant. The polar character of water makes it an excellent solvent for polar and ionic substances. (vi) It is a poor conductor of electricity. (vii) It has the tendency to associate. It exists in the liquid state not as a single H2O molecule but as associated molecules through hydrogen bonding. The existence of hydrogen bonding is responsible for high values of specific heat, the latent heat of fusion and latent heat of vaporisation. (b) Chemical properties (i) Water is neutral in nature. pH of the pure water is 7. It is a weak electrolyte and feebly ionises into H+ and OH– ions. H 2O H+ + OH– In pure water [H+] = [OH–] = 10–7 at 25°C. (ii) WITH METALS : it reacts with active metals and evolves hydrogen. The reaction is exothermic in the case of alkali and alkaline earth metals. 2Na+ 2H2O 2NaOH + H2 Ca + 2H2O Ca(OH)2 + H2 (iii) REACTION WITH NON METALS Chlorine decomposes cold water forming HCl and HClO. Cl2 + H2O HCl + HClO (Hypochlorous acid ) When steam is passed over red hot coke (1000°C), water gas is formed. C  H 2 O  CO  H 2 14 2 43 Water gas (iv) ACTION ON NONMETALLIC OXIDES : Acidic oxides combine with water to form acids. CO2 + H2O ƒ (v) H2CO3 (Carbonic acid) SO2 + H2O H2SO3 (Sulphurous acid) SO3 + H2O H2SO4 (Sulphuric acid) P2O5 + 3H2O 2H3PO4 (Orthophosphoric acid) N2O5 + H2O 2HNO3 (Nitric acid) Cl2O7 + H2O 2HClO4 (Perchloric acid) ACTION ON METALLIC OXIDES : basic oxides combine with water to form alkalies. Na2O + H2O 2NaOH CaO + H2O Ca(OH)2 (vi) ACTION ON HYDRIDES, CARBIDES, NITRIDES, PHOSPHIDES : Water decomposes these compounds with liberation of hydrogen, acetylene (or methane), ammonia, phosphine respectively. CaH2 + 2H2O Ca(OH)2 + 2H2 CaC2 + 2H2O Ca(OH)2 + C2H2 Al4C3 + 12H2O 4Al(OH)3 + 3CH4 Mg3N2 + 6H2O 3Mg(OH)2 + 2NH3 Ca3P2 + 6H2O 3Ca(OH)2 + 2PH3 (vii) HYDROLYSIS : Many salts specially the salts of strong bases with weak acids,weak bases with strong acids and weak bases with weak acids undergo hydrolysis with water. CH3COONa + H2O  CH3COOH + NaOH CH3COONH4 + H2O  CH3COOH + NH4OH Halides of nonmetals are decomposed by water. PCl5 + 4H2O H3PO4 + 5HCl PCl3 + 3H2O H3PO3 + 3HCl HYDROGEN AND ITS COMPOUNDS HARD AND SOFT WATER A water is said to be a soft water if it produces sufficient lather with the soap and water is described as being hard if it forms an insoluble scum before it forms a lather with soap. The hardness of natural water is generally caused by presence of bicarbonates, chlorides and sulphates of calcium and magnesium but infact soluble salts that form a scum with soap cause hardness. Ca2+(aq) + 2C17H35COO– (aq) (C17H35COO)2Ca Mg2  (aq)  2C 17 H 3 5 COO  (aq) ( C 17 H 35 COO )2 Mg Anion of soap Inso lub le precipitates Soap will not produce lather with water until all the calcium and magnesium ions have been precipitated. Hard water thus wastes soap. Hardness of water is of two types : (a) Temporary hardness (b) Permanent hardness (a) Temporary hardness : This is due to the presence of bicarbonates of calcium and magnesium. Temporary hardness in water is easily removed by boiling, as the bicarbonates decompose readily and the insoluble carbonates are precipitated. Boil Ca(HCO 3 )2   CaCO 3  H 2 O  CO 2 (Inso lub le ) Boil Mg(HCO 3 )2   MgCO 3  H 2 O  CO 2 (Inso lub le ) Temporary hardness can also be removed by Clark's process which involves the addition of slaked lime [Ca(OH)2]. Ca(HCO3)2 + Ca(OH)2  2 CaCO + 2H2O (Inso lub le ) It is essential to add only the calculated amount of Ca(OH)2 because excess will cause artificial hardness. (b) Permanent hardness : Permanent hardness is introduced when water passes over rocks containing the sulphates or chlorides of both of calcium and magnesium. This type of hardness cannot be removed by boiling or by the addition of slaked lime. The various water softeners are : (i) Washing soda : It removes both the temporary and permanent hardness by converting soluble calcium and magnesium compounds into insoluble carbonates. CaCl2 + NaCO3 = CaCO3 + 2NaCl CaSO4 + Na2CO3 = CaCO3 + Na2SO4 Ca(HCO3)2 + Na2CO3 = CaCO  2 NaHCO 3 (Inso lub le ) (So lub le ) In place of sodium carbonate, caustic soda or sodium phosphate can also be used. MgCl2 + 2NaOH  Mg(OH )2 + 2NaCl (Inso lub le ) 3MgSO4 + 2Na3PO4  Mg 3 (PO 4 )2 + 3Na2SO4 (Inso lub le ) (ii) Calgon : The complex salt of metaphosphoric acid, sodium hexametaphosphate (NaPO3)6, is known as calgon. It is represented as Na2[Na4(PO3)6]. Calcium and magnesium salts present in hard water react with calgon to give complex salts. 2CaSO4 + Na2[Na4(PO3)6] Na2[Ca2(PO3)6] + 2Na2SO4 2MgSO4 + Na2[Na4(PO3)6] Na2[Mg2(PO3)6] + 2Na2SO4 (iii) Permutit process : Permutit is hydrated sodium alumino silicate [Na2Al2Si2O8. xH2O] [Na2O.Al2O3.2SiO2.xH2O] Permutit also known as sodium zeolite (Na2Z). means Zeolite is Al2Si2O8.xH2O. In this process when hard water is poured into chamber, it may contain organic impurities like plant. This impurities can be removed by gravel. Hard water NaCl solution On moving upwards hard water will react with Na2Z during this reaction Na+ ions of Na2Z will replace Mg+2 & Ca+2 of impurities. Na2Z Soft water Graves Na2Z + CaCl2 2NaCl + CaZ NaCl is dissolved in water & water becomes soft. Impurities This soft water is fit for washing purpose but not fit for drinking purpose. After some time when Na2Z is completely converted into CaZ. Process is stopped and for regeneration of Na2Z. We use NaCl solution. 2NaCl + CaZ CaCl2 + Na2Z (iv) Ion exchange resin : By this process we can remove both cation & anion of hardness. This process contain two chamber. (a) Cation exchange resin : This resin contains granular insoluble organic acid having giant molecules with –COOH group. (b) Anion exchange resin : This resin contain giant organic molecules with basic groups derived from amines. R–NH3+OH– Process : When hard water is poured into first chamber the cation of hardness (Mg+2. Ca+2) removed by H+ ions of organic acid. 2R–COO–H+ + CaCl2 (R–COO)2Ca + 2H+ + 2Cl– + MgSO4 (R–COO)2Mg + 2H+ + SO4–2 HYDROGEN AND ITS COMPOUNDS Impure water H ,Cl ,SO4 + - 2- Ca ,Na ,SO4 ,Cl 2- - Anion exchanger Cation exchanger Waste Waste Alkali for regeneration + Dilute acid for regeneration 2+ Pure water This water becomes soften but not used for drinking purpose because this water contain the impurity of acid. To remove anion of hardness this acidic water then passed through another bed containing anion exchanger. This exchanger removes anion like Cl–, SO4–2 & HCO3–. R–NH3+OH– + H+ + Cl– R–NH3+Cl– + H+OH This water is free from impurities & can be used for drinking purpose. After some times when both resin gets exhausted process is stopped. Regeneration of resin (i) Cation exchange resin : We use dil acid. 2H+Cl– + (R–COO)2Ca  2R–COO–H+ + CaCl2 (ii) Anion exchange resin : We use dil NaOH solution R–NH3+Cl– + Na+OH– Na+Cl– + R–NH3+OH– HEAVY WATER (D2O) METHOD OF PREPARATION Repeated electrolysis of H2O : On electrolysis of water (impure) H2O dissociate into H+ & OH– while a fractional part of D2O will dissociate into D+ & OD– H 2O ƒ H+ + OH– D 2O ƒ D+ + OD– D+ & OD– due to more mass have less mobility i.e. why H+ & OH– will move towards cathode & anode respectively while D+ & OD– will be in solution. This process will repeated for six time. PROPERTIES OF HEAVY WATER Physical properties : (a) Heavy water is a colourless, odourless and tasteless mobile liquid, (b) Nearly all the physical constants are higher than the corresponding values of ordinary water. Chemical properties : Heavy water is chemically similar to ordinary water. However, D2O reacts more slowly than H2O in chemical reactions. (a) ACTION OF METALS : D2O reacts with alkali and alkaline earth metals liberates heavy hydrogen. 2D2O + 2Na  2NaOD + D2 Sodium deuteroxide 2D2O + Ca  Ca(OD)2 Calcium deuteroxide (b) + D2 ACTION WITH METALLIC OXIDES : D2O reacts slowly with basic oxides to form heavy alkalies. Na2O + D2O 2NaOD CaO + D2O Ca(OD)2 (c) ACTION WITH NONMETALLIC OXIDES : D2O reacts slowly with acidic oxides to form deutero acids. N2O5 + D2O  2 DNO 3 Deutero nitric acid P2O5 + 3D2O  SO3 + D2O  (d) 2 D PO 3 4 Deutero phosphoric acid D SO 2 4 Deutero sulphuric acid ACTION WITH METALLIC CARBIDES, PHOSPHIDES, NITRIDES, ARSENIDES, ETC. : Like H2O heavy water reacts with carbides, phosphide nitrides, arsenides, etc. to form corresponding deutero compounds. CaC2 + 2D2O Ca(OD)2 + C D 2 2 Deutero acetylene Al4C3 + 12D2O 4Al(OD)3 + 3 CD 4 Deutero methane Mg3N2 + 6D2O 3Mg(OD)2 + AlN + 3D2O Al(OD)3 + ND 3 Deutero ammonia Ca3P2 + 6D2O 3Ca(OD)2 + Na3As + 3D2O 3NaOD + (e) 2 ND 3 Deutero ammonia 2 PD 3 Deutero phosphine AsD 3 Deutero ar sin e ELECTROLYSIS : A solution of heavy water containing Na2CO3 when electrolysed evolve heavy hydrogen at cathode. Electrolysis 2D 2 O   2D 2  O 2 (Cathode ) (Anode ) USES : As a neutron moderator : Fission in uranium-235 is brought by slow speed neutrons. The substances which are used for slowing down the speed of neutrons are called moderators. Heavy water is used for this purpose in nuclear reactors. HYDROGEN AND ITS COMPOUNDS H2O2 (Hydrogen Peroxide) LABORATORY METHOD In laboratory, H2O2 is prepared by adding calculated amounts of sodium peroxide to ice cod dilute (20%) solution of H2SO4. Na2O2 + H2SO4 Na2SO4 + H2O2 By the action of sulphuric acid or phosphoric acid on hydrated barium peroxide BaO2.8H2O (Merck process) (a) BaO2.8H2O + H2SO4 BaSO4+H2O2 + 8H2O Anhydrous barium peroxide does not react readily with sulphuric acid (because a coating of insoluble barium sulphate is formed on its surface which stops further action of the acid). Therefore, hydrated barium peroxide, BaO2.8H2O must be used. (b) 3BaO2 + 2H3PO4  Ba3(PO4)2 + 3H2O Ba3(PO4)2 + 3H2SO4  3BaSO4 + 2H3PO4 Phosphoric acid is preferred over H 2 SO 4 because soluble impurities like barium persulphate (BaO2.8H2O –H2SO4) tends to decompose H2O2 while H3PO4 acts as preservative (negative catalyst) for H2O2. INDUSTRIAL METHOD (i) Auto oxidation of 2 butyl anthraquinol ( cyclic process) OH O C4H9 O 2 ‡ˆ ˆˆHˆˆ ˆ† ˆˆ 2 OH (ii) O Oxidation of isopropyl alcohol CH3—CH—CH 3 + O2 CH3 C CH3 OH (iii) C4 H 9 H 2O 2 + + H2O2 O Electrolytic Process : Used 50% H2SO4 in electrolytic cell using Pt as anode graphite as cathode. 2H2SO4 2H+ + 2HSO4 At Cathode 2H+ + 2e– H2  At Anode 2HSO4– H2S2O8 + 2e–| Peroxo disulphhuric acid H2S2O8 + H2O  H2SO4 + H2SO5 H2SO5 + H2O  H2SO4 + H2O2 Physical property (i) Pure H2O2 is colour less, odourless liquid and impure with bluish layer. (ii) It has more Hydrogen bonding then H2O, So order of boiling point. H 2 O 2 > D 2 O > H 2 O (iii) It is soluble in H2O, alcohol and ether (iv) It has bitter test and harmful for skin (v) It is a dibasic weak acid (vi) It has a oxidising as well as reducing property (vii) H2O2 easily decompose in presence of light and temperature, So H2O2 always kept in dark bottles and kept at cool places. (viii) 30% solution of H2O2 is called Perhydrol. Chemical property 1. STABILITY : It is unstable in nature decompose on standing and heating. It is an example of auto oxidation-reduction Reaction ; H2O2  H2O + O NOTE : Nascent oxygen working as colourless agent Decomposition of H2O2 ; 2H2O2 ‡ˆ ˆˆ ˆ† ˆˆ 2H2O + O2 Note : This is retarded by R–OH, acetanilide, glycerol 2. OXIDIZING NATURE : H2O2 is a powerful oxidant in acidic as well as in alkaline medium. (In acid) Fast H2O2 + 2H+ + 2e   2H2O E0RP  1.77V (In alkali) – Slow H2O + HO2– + 2e   3HO E0RP  0.87 V Thus H2O2 is more powerful oxidant in acidic medium. The simple interpretation of H2O2 as oxidant can be shown by the equation. H2O2 H2O + O Following are some important examples of oxidant action of H2O2 : (a) H2O2 oxidises black lead sulphide (PbS) to white lead sulphate (PbSO4). This reaction is used in restoring the white colour of old paintings which have blackened due to the formation of lead sulphide by the action of H2S present in air. 4[H2O2 H2O + O] PbS + 4O PbSO4  (b) PbS + 4H2O2 PbSO4 + 4H2O H2O2 oxidises sulphites into sulphates. H2O2 H2O + O Na2SO3 + O Na2SO4  (c) Na2SO3 + H2O2 Na2SO4 + H2O H2O2 oxidises nitrites to nitrates. H2O2 H2O + O Na2NO2 + O NaNO3  (d) Na2NO2 + H2O2 Na2NO3 + H2O H2O2 oxidises H2S into sulphur. H2O2  H2O + O H2S + O  H2O + S  H S + H O 2H O + S HYDROGEN AND ITS COMPOUNDS 3. Reducing nature : It can also act as a reducing agent towards powerful oxidising agents. H2O2 2H+ + O2 + 2e– (a) It reduces Ag2O to silver. Ag2O + H2O2 2Ag + H2O + O2 (b) It reduces ozone to oxygen. H2O2 + O3 H2O + 2O2 STRUCTURE OF HYDROGEN PEROXIDE H The vapour density as determined by Victor O Meyer method at 90°C is 17. Hence, the molecular O H Kingzett's formula mass of H 2O 2 is 34. Two formulae have been suggested for hydrogen peroxide. H–O–O–H Baeyer's formula The calculated value of the single bond O–O distance is 1.48Å and X-ray measurements shows H 2.1 D. This suggests that all the four atoms do not lie O O × 1.46 + 0.03Å. The value of dipole moment of H2O2 is × what in hydrogen peroxide, O–O bond distance is H or 111°. The hydrogen atoms are present one on each H cover and H–O bonds making angles of 94° with the O–O bond as shown in fig. The bond distance between O–H is 0.97Å. H 94° 94° O H in the same plane. The molecule can be pictured as lying on the spine of a book open to an angle of O H O 1.48Å O 7Å 0.9 (A) 7Å 0.9 111° (B) Precautions (i) H2O2 can not be stored in simple glass bottles since rough surface of glass [alkali oxides present in it] excited by light and decomposed H2O2. So the H2O2 usually stored in coloured, paraffin wax coated, plastic bottle. (ii) Always with H2O2 add small quantity of inhibitor or negative catalyst to stay decomposition of H2O2. likeH3PO4, acetanilides etc. KEY POINTS Uses of H2O2 (i) Bleaching agent (ii) Hair dying (iii) H2O2 + N2H4 as Rocket propellent (iv) H2O2 as oxidant and reductant (v) Antiseptic Ex. What causes the temporary and permanent hardness of water ? Sol. Temporary hardness is caused by presence of soluble bicarbonates of calcium and magnesium, i.e. Ca(HCO 3)2 and Mg(HCO3)2 in water whereas permanent hardness is caused by presence of soluble chlorides and sulphates of calcium and magnesium, i.e. CaCl2, CaSO4, MgCl2 and MgSO4 in water. Ex. What is 'demineralised water' and how can it be obtained ? Sol. Water which is free from all cations and anions is called demineralised water. It is obtained by passing hard water first through cation exchange resin and then through anion exchange resin. Ex. Explain the following : (i) Soft water lathers with soap but not hard water. (ii) Temporary hard water becomes soft on boiling. (iii) Water can extinguish most fires but not petrol fire. (iv) Hard water is softened before use in boilers. Sol. (i) Hard water contains calcium and magnesium salts. These react with soap to form insoluble calcium and magnesium salts of fatty acids, i.e., form scum and not lather. 2RCOONa (soap) + Ca2+  (RCOO)2 Ca (insoluble) + 2Na+ 2RCOONa (soap) + Mg2+  (RCOO)2 Mg (insoluble) + 2Na+ (ii) Temporary hardness of water is due to the presence of soluble bicarbonates of calcium and magnesium. On boiling, the bicarbonates are converted into insoluble carbonates which can be removed by filtration. Ca(HCO3)2 (soluble)  CaCO3  + H2O + CO2 Mg(HCO3)2 (soluble)  MgCO3  + H2O + CO2 (iii) When water poured over petrol fire, petrol being lighter than water floats over water and thus fire spreads instead being extinguished. (iv) Hard water consists bicarbonates and other soluble salts of calcium and magnesium. When hard water is evaporated in boilers, scales of precipitated carbonates of calcium and magnesium along with other salts such as sulphates, chlorides, etc., are formed. In order to avoid the formation of scales hard water is first softened before use in boilers. Ex. What happens when ? (i) Heavy water reacts with magnesium nitride. (ii) Heavy water reacts with sodium. Ans. (i) Mg3N2 + 6D2O  Mg(OD)2 + 2ND3 (Deutrammonia) (ii) Na + 2D2O  2NaOD + D2 Ex. Sol. Knowing the properties of H2O and D2O, do you think that D2O can be used for drinking purposes? Heavy water is injurious to human beings, plants and animals since it slows down the rates of reactions occuring in them. Thus, heavy water does not support life. In fact it retards certain cellular process, such as mitosis, cell division, etc, Thus, prolonged use of D2O leads to degeneration of tissues. HYDROGEN AND ITS COMPOUNDS Ex. Assertion : Anhydrous BaO2 is not used for preparing H2O2. Reason : H2O2 is prepared on large scale by air oxidation of 2-Ethyl anthraquinol. (1) If both Assertion and Reason are true and Reason is a correct explanation of Assertion. (2) If both Assertion and Reason are true and Reason is not a correct explanation of Assertion. (3) If Assertion is true but Reason is false. (4) If Assertion is false but Reason is true. Sol. Assertion : BaO2 + H2SO4  BaSO4  (white) + H2O2 Insoluble BaSO4 forms a thin layer around BaO2 and therefore reaction occurs slowly and finally stops. So anhydrous BaO2, is not used. Reason : Industrial method (Auto oxidation) OH O C2H5 OH O2 (air) (Oxidation) H2 (Ni) (Reduction) C2H5 + H2O2 O 2- Ethyl anthraquinol 2-Ehtylanthraquinone It is cheaper method as only O2 from air and H2 are consumed. Ex. Sol. Ans. (2) Write chemical reactions to justify that hydrogen peroxide can function as an oxidising as well as a reducing agent. H2O2 can act as an oxidising as well as a reducing agent both in acidic and basic media as illustrated below. (i) Oxidising agent in acidic medium 2Fe2+(aq) + 2H+(aq) + H2O2(aq)  2Fe3+(aq) + 2H2O() (ii) Oxidising agent in basic medium Mn2+(aq) + H2O2(aq) + 2HO–(aq)  MnO2(s) + 2H2O() manganese dioxide (iii) Reducing agent in acidic medium 2MnO4(aq) + 6H+(aq) + 5H2O2(aq)  2Mn2+(aq) + 8H2O() + 5O2(g) (iv) Reducing agent in basic medium Ex. Sol. Explain the following : (i) Why hydrated barium peroxide is used in the preparation of hydrogen peroxide instead of the anhydrous variety ? (ii) Phosphoric acid is preferred to sulphuric acid in the preparation of H2O2 from barium peroxide. (iii) Statues coated with white lead on long exposure to atmosphere turns black and the original colour can be restored on treatment with H2O2. (i) If anhydrous barium peroxide is used in the preparation, the barium sulphate, thus formed, forms an insoluble protective coating on the surface of solid barium peroxide hydrated. This prevents the further reaction of the acid, i.e., causing the reaction to stop. If, however, hydrated barium peroxide (in the form of the paste) is used, the water causes to dislodge the insoluble BaSO 4 from the surface of BaO2. Hence BaSO4 settles at the bottom of the reaction vessel and the reaction continues without any difficulty. (ii) When phosphoric acid is used in the preparation of H2O2 from BaO2, it plays the dual role. It liberates H2O2 and also acts as a preservator by retarding its decomposition. (iii) White lead is used as a pigment. The statues coated with white lead get blackened due to the action of H 2S present in atmosphere in traces. Pb(OH)2 (white lead).2PbCO3 + 3H2S  3PbS + 2CO2 + 4H2O DIHYDROGEN AS A FUEL Dihydrogen releases large quantities of heat on combustion. The data on energy released by combustion of fuels like dihydrogen, methane, LPG etc. are compared in terms of the same amounts in mole, mass and volume, are shown in Table THE ENERGY RELEASED BY COMBUSTION OF VARIOUS FUELS IN MOLES, MASS AND VOLUME Energy released on combustion in kJ state) Dihydrogen (in gaseous state) Dihydrogen (in liquid) LPG CH4 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 From this table it is clear that on a mass for mass basis dihydrogen can release more energy than petrol (about three times). Moreover, pollutants in combustion of dihydrogen will be less than petrol. The only pollutants will be the oxides of dinitrogen (due to the presence of dinitrogen as impurity with dihydrogen). This, of course, can be minimised by injecting a small amount of water into the cylinder to lower the temperature so that the reaction between dinitrogen and dioxygen may not take place. However, the mass of the containers in which dihydrogen will be kept must be taken into consideration. A cylinder of compressed dihydrogen weighs about 30 times as much as a tank of petrol containing the same amount of energy. Also, dihydrogen gas is converted into liquid state by cooling to 20K. This would require expensive insulated tanks. Tanks of metal alloy like NaNi5, Ti–TiH2, Mg–MgH2 etc. are in use for storage of dihydrogen in small quantities. These limitations have prompted researchers to search for alternative techniques to use dihydrogen in an efficient way. In this view Hydrogen Economy is an alternative. The basic principle of hydrogen economy is the transportation and storage of energy in the form of liquid or gaseous dihydrogen. Advantage of hydrogen economy is that energy is transmitted in the form of dihydrogen and not as electric power. It is for the first time in the history of India that a pilot project using dihydrogen as fuel was launched in October 2005 for running automobiles. Initially 5% dihydrogen has been mixed in CNG for use in four-wheeler vehicles. The percentage of dihydrogen would be gradually increased to reach the optimum level. Nowadays, it is also used in fuel cells for generation of electric power. It is expected that economically viable and safe sources of dihydrogen will be identified in the years to come, for its usage as a common source of energy. HYDROGEN AND ITS COMPOUNDS TIPS & FORMULAS Preparationof hydrogen (I) Passing steam over hot iron (Lane process) 3Fe + 4 H2O  Fe3P4 + H2  (II) By the action of water on hydrolith (III)  Ca(OH)2 + 3H2 CaH2 + H2O  By the electrolysis of water (IV) Bosch process  CO + H2 C(s) + H2O (g)  + FeCrO 4 H2O(g)   CO2 + H2  25 atm H 2O CO2 absorbed Properties of molecular hydrogen Metals like Pd, Pt, Ni, Co etc. adsorb large quantities of the gas due to vacancies between these atoms. This is known as "occlusion". Reaction with vegetable oils Vegetable oil + H2 473 K Ni Vegetable gheef (Slid fat) This process is known as "hydrogenation" or "hardening of oils" Isotopes of hydrogen (a) Hydrogen (Protium) 1 1H or H (P = 1, e = 1, n = 0) (b) Deuterium 2 1H or D (P = 1, e = 1, n = 1 Different forms ofhydrogen Atomic hydrogen H2 electricarc   2H (Molecular hydrogen) (Atomic hydrogen) Nascent hydrogen  ZnSO4 + 2H Zn + dil.H2SO4  Ortho and Para hydrogen If two nuclei have same spin then it is called "Ortho H2". If two nuclei have different spin then it is called "Para H2". HYDRIDES (c) Tritium 3 1H or T (P = 1, e = 1, n = 2) Ionic or salt like hydrides : s block Li H, NaH, KH, RbH, SrH2, BaH2 etc. Be & Mg hydrides are covalent in nature Molecular or covalent hydrides : p block NH3, PH3, H2O, CH4 etc. Metallic or Interstitial hydrides : trasition elements In these hydrides, hydrogen atoms occupies the interstitial position of metallic latice. La H2.87, Ti H1.8, Zr H1.9 Hydride gap = 7, 8, 9 WATER (I) The existence of hydrogen bonding is responsible for high values o specific heat, the latent of fusion and latent heat of vapourisation and high boiling point. (II) Some of the covalent compounds such as alcohols, carboxylic acids and carbohydrates are soluble in water due to formation of hydrogen bonding. Hardness of Water Temporary hardness of water is due to bicarbonates of Ca and Mg. It can be removed by – (a) Boiling (b) Clark method using CaO Permanent hardness of water is due to chloride/sulphate of Ca and Mg. It can be removed by – (a) (b) (c) (d) Adding washing soda, Na2CO3 Calgon [Na6(PO3)6] Permutit, Na2 Al2 Si2 O8. xH2O Artificial resins, RSO3H & RNH2OH Heavy water or Deuterium oxide (D2O) (a) It is produced by repeated electrolysis of ordinary water containing alkali. (b) Most important use of heavy water is in nuclear reactors for slow down the speed of neutron (i.e. as a moderator) HYDROGEN PEROXIDE Preparation (I) (II) (III) (IV) (V)  BaSO4 + H2O2 + 8 H2O BaO2 . H2O + H2SO4   2 Na2SO4 + H2O2 Na2O2 + 2 H2SO4   BaCO3 + H2O2 BaO2 + H2O + CO2  Oxidation of 2 Alkyl anthraquinol Electrolysis of 50% H2SO4 Chemical properties (a) Decomposition 2H2O2 reduction H2O + O2 oxidation (b) (c) H2O2 can accept as well can donate electrons and thus it can acts as an oxidising and reducing agtent in acidic as well as alkaline medium Oxidising properties : It is a strong oxidising agent under acidic and alkaline conditions. Oxidation in HYDROGEN AND ITS COMPOUNDS acidic medium is generally slow while rapid in alkaline solution.  2 H2O H2O2 + 2H+ + 2e  In alkaline solution  2 H2O + 2O2– H2O2 + 2OH– + 2e  (d) Reducing properties It acts as a reducing agent towards strong oxidising agents in acidic as well as alkaline medium. Reducing action in acidic solution is slower than in alkaline solution. (e) Bleaching action Structure  H2O + [O] H2O2  H O H O 94°48' Open book structure 111°30' Structure of H2O2 in the gas phase. Tests of H2O2 (a) It liberates iodien from KI solutin in the presence of ferrous sulphate. (b) It gives orange red colour with acidified titanium oxide due to formation of pertitianic acid. (c)  H2TiO4 + 2 H2SO4 Ti(SO4)2 + H2O2 + 2H2O  It gives blue colour with acidicfied K2Cr2O7 and ether. The blue colour of chromium peroxide is stabilized by ether.  CrO5 + 3H2O CrO42– + 2H+ + 2H2O2 