HYDROGEN - Lecture Notes

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) UNIT 9 HYDROGEN  Most abundant & lightest in the universe [Earth O ] 2  Combines with all others except noble gases  Largest no.of compounds than others  Ist isolated by-Henry Cavendish  Name given by - Lavoisier  Hydrogen means - Water generator Atomic structure  Simplest of all  Has a proton and an electron  No neutrons Attainment of stability 1) By gaining – H 1e  H NaH, CaH2, MgH2 etc 2) By sharing – By covalent bonding H2O, NH3, CH4 etc 3) By losing – H  H 1e H+ is – Highly polar – Equivalent to a portion – Associated with others H2O  H  H3O Polar – can make distortion in electron cloud of other molecules /ions Position in the periodic table – Ist element –Not in any group Has similarities with alkali metal and halogens 1

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) Similarities with Alkali metals 1) Electric configuration  Both have ns1 as general valence shell configuration. H–1s1 Li – 1s22s1, Na – 1s22s22p6 2) Electro positive H  H 1e  Na  Na 1e  Release an electron to form unipositive ions. 3) Liberation at cathode  During electrolysis of Halides of both, H+ andAlkali metal ions liberate at cathode NaCl  Na  Cl HCl  H  Cl 4) Reducing power Fe2O3  2H2  2Fe  3H2O B2O3  6Na  2B  3Na 2O  Both are good reducing agents 5) Affinity for electro –ve elements  Both have great affinity towards non metals.  Form compounds like HCl, H2O, H2S etc similar to NaCl, Na2O, Na2S etc Differences:- 1) Alkalimetals – Typical Metals Hydrogen – Non metal 2) H has high I.E 2 H – 1312 KJ/mol Li – 520 KJ/mol, Na – 495 KJ/mol, K – 418 KJ/mol 3) H+ has small size 4) H+ is equivalent to a proton Resemblance with Halogens 1) Electronic configuration  Both have valence electrons 1 less than nearest noble gas H 1s1  He 1s2 F 1s2 2s2 2p5  Ne 1s2 2s2 2p6 2) Atomicity H2 F2 , Cl2 , Br2 , I2 Both are diatomic 2

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) 3) Ionization enthalpy H2 – 1312 kJ/mol, F –1681 KJ/mol, Cl–1256 KJ/mol, Br– 1143 KJ/mol, I–1009 KJ/mol Both have comparable I.E 4) Electro negative character H 1e  H Cl 1e  Cl Both accept an electron to form monovalent anions 5) Liberation at Anode NaH  Na  H NaCl  Na  Cl On electrolysis of metal hybrid and metal halides, both H– and Halide ions move towards anode Differences • H has samller tendency to form H– than halogens. 2 • Absence of non bonded electrons in H2 [but halogens have] H H Cl Cl Dihydrogen (H2) Various forms of Hydrogen • Universe – most abundant 70% • 90% solar atmosphere • Doesn’t occur in earth’s atomsphere • Seen as combined form 1) Isotopic Forms 1) Protium (P) • Normal hydrogen • Represented as H11 • e–1 P–1 n–0 • Atomic No–1 • Mass No – 1 • Abundance –99.98% 2) Deuterium (D) • Heavy hydrogen • Represented as H12 • e–1 P–1 n–1 • Atomic No –1 3

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) • Mass No – 2 • Abundance –0.0156% 3) Tritium (T) • Radio active ( –rays) • Represented as H13 • e–1 P–1 n–2 • Atomic No–1 • Mass No – 3 • Abundance – 4×10–15% Chemical properties:- • Identical • Due to same no. of e physical properties • Different • Due to different masses 1) Isotopic effect Property difference due to difference in mass no. 2) Isomeric forms A) H2 HH OO • Same nuclear spin direction. • Called ortho hydrogen • More stable • Abundance - 75% at 300 K B) H2 HH OO • Opposite nuclear spin direction. • Called para hydrogen • Less stable • Abundance - 25% at 300 K 3) Molecular hydrogen – H2 • Most stable form • Least Reactive form 4) Nascent hydrogen 2[H] • Newly formed 4

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) • Nascent hydrogen Just displaced from a compound • More reactive than H2 • Less stable than H2 5) Atomic hydrogen -H • By splitting of H 2 • Exist only at high T (4000-5000K0 • Least stable • Most reactive • Used in atomic hydrogen torch Preparation of H2 a) Laboratory preparation By decomposing water, acids, alkalis etc. A) From water 1) Alkali metals – Violent reaction With water  H gas 2 2Na+2H2O  2NaOH+ H2 2) Alkaline earth metals – slow reaction with water  H gas 2 Mg+2H2O  Mg OH2 + H2 3) Metals decompose steam to produce their oxides by liberating H gas. 2 3Fe+4H2O  Fe3O4 + 4H2 b) Hydrides of alkali metals and alkaline earth metals, when dissolved in H2O produce H2 NaH  H2O  NaOH + H2 CaH2  2H2O  Ca OH2 + 2H2 B) From acids • Metal like Zn, Mg, Fe liberate H gas from acids 2 Zn  2HCl  ZnCl2  H2 Zn  H2SO4  ZnSO4  H2 2Al  3H2SO4  Al2 SO4 3  3H2 * Reactive metals to be used * Dil. acid to be used If con. H2SO4–SO2 produced instead of H2 gas 5

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) C) From Alkalis 2Al  2NaOH  2H2O  2NaAlO2  3H2 Zn  2NaOH  Na2ZnO2  H2 Note:- High pure hydrogen (99.95) • Dil. H SO +Mg Ribbon 24 Mg  H2SO4  MgSO4  H2 • Electrolysis of warm Ba(OH)2 • Water + NaH • KOH + Scarp Al 2Al+ 2KOH 2H2O 2KAlO2+ 3H2 Industrial preparation a) Electrolysis of acidified H O 2 2H2O  2H2  O2 • Pt as electrods b) Lanes process • Steam passed through sponge from 3Fe  4H2Og 7731050K Fe3O4  4H2 FeO4 – Ferrosoferric oxide Reduction Step Fe3O4  4H2  3Fe  4H2O Fe3O4  4Co  3Fe  4Co2 2) Bosch Process • Super heated steam passed through Red hot coke • Water gas is formed C+H2O 1270K CO + H2 CO:H2 4:5 • Water gas again mixed with steam in the presence of Fe2O3 and Cr2O3 CO  H2  H2O Fe2O6373CKr2O3 CO2  2H2 Fe2O3 – Catalyst 6

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) Cr2O3 – Promoter CO2  H2O – Passed through water at high P CO2 – dissolve in H2O H2 – Collected by absorbing in an alkali 2H2  CO2  2NaOH  Na2CO3  H2O  2H2 4) Hydrocarbon steam process • Modern method • Principal source of H2 • Natural gas [CH4] mixed with steam CH4  H2Og 1270K CO  3H2 Ni • H2 collected as in Bosch process. As a Biproduct • Obtained on a large scale as a biproduct in the manufacture of many industrially important compounds Eg : NaOH Electrolysis of Brine 2NaCl  2H2O  2NaOH  Cl2  H2 Physical Properties of H 2 • Colourless • Odourless • Slightly soluble in H O 2 • Liquified only at very low T (Tc = –2530C) • H2 – Non planar • High thermal stability Chemical Properties • H molecule – Thermally stable 2 • Very difficult to break at normal temperature [Highly exothermic] a) Combustibility • Highly combustibile gas • Burns in air to form H2O 2H2  O2  2H2O; H  285 KJ/mol 7

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) b) Reducing Property • Metal oxides –heated with H2mreduced – metal is formed CuO  H2  Cu  H2O Some chlorides are also reduced 2AgCl  H2  2Ag  2HCl c) Reaction with non metals.  with dioxygen H2O  with dinitrogen  NH 3  with halogens  HX H2  X2  2HXX, F, Cl, Br, I with F–Reacts even at dark with I – needs a catalyst d) Reaction with organic compound 1) Hydrogenation • With unsaturated organic compounds, forms saturated C2H4 NiC2H6 Hydrogen gas – pass through veg. oils – converted to fat – vanaspati ghee – 2) Hydroformylation CO  H2  R  CH  CH2  R  CH2  CHO H2 R  CH2CH2OH Hydroformylation – addition of a hydrogen atom and a formyl group (–CHO) to a C=C e) Reaction with metals 1 2Na  H2  2 Na H 0 2 Ca H2  Ca H2 Shows oxidising property of H 2 Uses of H gas 2 1) Manufacture of HCl, NH , CH OH, HNO etc 33 3 2) Hydrogenation of oil 3) Filling aeroplane tyres [85% He+15% H ] 2 8

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) 4) Atomic hydrogen torch 5) As a rocket fuel 6) Fuel cell 7) Reducing agent Compounds of hydrogen Hydrides • Binary compounds of H2 with other elements • Three type (1) Ionic | salt like | Saline  Formed by S - Blocks  NaH, CaH , etc 2  electro –veity <2.1  O.S of the H = –1 2 • Crystalline solids • Non volatile [stable] • Solid form – Non conducting • Molten/aqueons – conduct • with H2O Alkaline soln and H2 gas. (2) Covalent /Molecular hybrides • With p –block [13–17] • H O, NH , CH , etc 2 34 • Covalent bonding • Prepared by: • Direct reaction of non-metals with hydrogen N2  3H2 Fe 2NH3 • Three type (1) Group 13 hydrides Eg: BH3/B2 H6 - Diborane • Central atom - Borone (5) Configuration – 2, 3 • Valance electrons - 3 HH B H • Central atom has only 6 es . 9

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) • Electron deficient • Act as electron acceptors • Lewis acids HH H BB HH H • Exist as dimeric form • (Polynuclear hydrides) Group-14 Eg: CH 4 Central atom – C(6). 2, 4 H HC H H • Central atom surrounded by 8 e • Known as e precise Group -15, 16, 17 Eg: NH3 Central atom – N(7) 2, 5 • HNH H • Central atom has compair • Also known as e ns Act as e donours in reactions • Lewis bases 3) Metallic hybrides or Interstitial/non–stoichiometric • On heating hydrogen reacts with many transition metals, lanthanides and actinides (d & f - block) • Such hybrides have metallic appearance • These are less dense than parent metal • Conduct heat and electricity [not well as parent metal] 10

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) • Here, hydrogen atoms seen inside the interstitial spaces of parent metals • Donot obey law of constant proportion. TiH1.51.8 VH0.56 NiH0.60.7 PdH0.60.8 TaH2.76 LaH2.87 etc. • Such hydrides are widely used in catalytic reduction and hydrogenation reaction • Metals like Ni, Pt, Pd, etc can accomodate a large amount of hydrogen gas Intermediate hydrides Hydride gap elements of group 7, 8 and 9 do not from hydrides Mn Fe Co | || 7, 8, 9 • Region of periodic table from 7, 8, 9 is referred to as hydride gap • These have low affinity to hydrogen in their normal oxidation states. Water [H2O] Most important substance known to man Abundantly found on earth. Found as - 1) Ice in mountains 2) Water in oceans, etc 3) Vapour in atmosphere • Covers about 3 quarters of earth • About 70% of human body is water Physical Properties Colourless, odourless, tasteless in pure form Molar mass – 18 g /mol • MP – 273 K BP – 373 K Density – 1g/cm3 Triple point • H2O exist in 3 phases • At 0.00980C and 4.58 mmHg H2Os  H2O  H2Og 11

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) Structure of water In the gaseous phase A water molecule consists of two hydrogen atoms joined to an oxygen atom by covalent bonds O H 104.5o H • Oxygen has 6 valence e • Valence s and p orbitals undergo sp3 hybridization • 4 sp3 hybrid orbitals • 2 will overlap with 1s orbitals of 2H atoms • Due to the presence of 2 lone pairs in O , bond angle of H–O–H bond will be reduced to 2 104.5o (109o 28') • Hence structure of water is Angular /bend. Polarity of water • O is more electronegative than H 22 • Pull the shared electron pairs more towards it. • Hence , H–O bond aquires polarity • Polarity result in association of water molecules • Gives a liquid phase with high BP,       HO H O HO H HH    Liquid phase water • H2O molecules are held by inter molecular hydrogen bonds H OH H OH OH HO H H HO H • One water molecule is surrounded by 4 other water molecules • Co-ordination no. of a water molecule is 4 12

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) Solid Phase • Crystalline form • By 2 ways • At atm pressure – crystallises into hexagonal form • Each oxygen is sorrounded by 4 other oxygen atoms • At very low T- crystallises in to cubic form. During crystallisation – in No. of H bonds – in volume   in density– floats on water surface During melting –breaking of H bonds,  in volume of water, with  in Temp– per min. Volume at 4oC -max. density of 1 g/ml at 4oC Chemical Properties of H2O 1)Amphoteric (Amphiprotic) • Can donate H+ (acid) as well as accept H+ (base) H2O  H  OH (acid) H2O  H  H3O (base) • Hence, water acts as a Lowry Bronsted Acid & Base • Substance behaving as acid and base - “Amphoteric ” Substance that can give as well as can accept a proton – Amphiprotic As an acid NH3  H2O  NH   OH 4 As a base : CH3COOH  H2O  CH3COO  H3O • Anion formed (OH–) due to the loss of H+  conjugate base  • Cation formed H3O due to the given of H+  conjugate acid Autoprotolysis also take place as H2O  H2O  H3O  OH 2) Redox Reactions with water Water reacts with highly electropositive metals 2Na  2H2O  2NaOH  H2O 2H2O  3Fe  Fe3O4  4H2 13

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) In above reactions, Na, Fe, etc got oxidised and H O is reduced. 2 Fluorine can oxidise water. 2F2  2H2O  4HF  O2 Hydrolysis Interaction of a cation or an anion or both with water. An acidic, basic or a neutral solution is formed. CO2  H2O  H2CO3  acidic NH3  H2O  NH4OH  basic Sugar solution – Neutral Hydration : Attraction of negative charged oxygen atom allows them to congregate around +ve ions  +ve charged hydrogen atoms gather around –ve ions • Water may exist as associated with other molecules or ions • 3 ways a) As co-ordinated b) As hydrogen bonded c) As interstitial a) Co-ordinated water Eg : H2O  H  H3O HO + H+ O H H HH CuSO4.5H2O  Cu H2O 4  SO4H2 b) Hydrogen bonded water CuSO4.5H2O  Cu H2O4  SO4H2O Hydrogen bonded c) Interstitial water BaCl .2H O 22 14

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) H H HO O H OH OS O O H HO Cu OH O H H HARDNESS  Purest form of water is rain water ( pH  7 )  Due to the presence of soluble salts of Ca/Mg  As M(HCO3), MCl2, MSO4, etc M  Ca / Mg  Soap do not form lather with hard water  Forms a precipitate CH3  CH2 16  COONa  CH3  CH2 16  COONa  Ca2 /Mg2 Sod. Stearate Stearate ion  CH3  CH2 16  COO 2 Ca Pr ecipitate Removal of Hardness A) If M HCO3 2 is present  Less stable compounds  Easy to Remove  Known as Temporary hardness Removal 1. Boiling Ca HCO3 2  CaCO3 H2O  CO2 Mg HCO3 2  Mg OH2  2CO2  Note If Mg(OH)2– Concentration of Mg2+ is only cube root of solubility product 15

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) In MgCO – Mg2+ concn. is square root of Ksp 3 2. Clark’s Method Calculated amount of lime is added to water Ca HCO3 2  Ca OH2  2CaCO3 2H2O Mg HCO3 2  2Ca OH2  2CaCO3  Mg OH2 2H2O B) If MCl2, MSO4, etc  Stable compounds  Not easy to Remove  Special methods are used 1. Treatment with Na CO 23 MCl2  Na 2CO3  MCO3 2NaCl MSO4  Na2CO3  MCO3 Na2SO4 2. Permutit Process  Zeolite is added to water Na2O. Al2O3. nSiO2. xH2O n = 5–13 x = 3–4  These are hydrated sodium aluminium silicates. NaAlSiO4.xH2O  Ca2 and Mg2 ions are replaced by Na ions 2NaZ  M2  MZ2  2Na  Zeolites can be regenerated by treating exhausted zeolite with NaCl MZ2  2NaCl  2NaZ  MCl2 3. Calgon Process  Na 2  Na 4  PO3   – Sodium hexametaphosphate is added to water 6 Na6P6O18  2Na  Na4P6O128 Na4P6O18  M2  Na2MP6O18  2Na  Na2 Na4 PO3 6   M2  Na2 M2 PO3 6  4Na Soluble complex 16

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry)  Ca2 and Mg2 ions in water are rendered ineffective by calgon, forming their soluble complexes in water – sequestration  This method is prefered for getting soft water for laundry purpose 4. Organic ion exchange Resin Resin - Long chain Hydrocarbons  Both cations and anions can be removed from water  2 steps Step I a) Using Cation Exchange Resin Long chain hydrocarbon, attached to an acidic group Eg. R– COOH Resin H  Cu2  Resin 2 Cu  2H b) Using Anion Exchange Resin  Long chain H.C, attached to a basic group OH Eg: R  NH4OH Resin  OH  Cl  Resin  Cl  OH H  OH  H2O  Resultant water  free from cation and anions.  Known as demineralized or deionized water Measurement of Hardness  Represented as degree of Hardness  Expressed in terms of amount of CuCO3, equivalent present in 106 parts of water  Unit - Parts Per Millian (ppm) Disadvantages of Hardness 1) Poor cleansing effect of soap 2) Boilet scale Heavy water (D2O)  Oxide of D2  Present in H2O (0.0156%)  1st isolated by Harold.C. Urey  By prolonged electrolysis of H2O containing small amount of NaOH  H O decomposes 1st 2 17

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry)  Resulting solution is rich in D O 2 Properties 1) Colourless, odourless, tasteless 2) Most of physical constants are higher than H2O H2O D2O BP 100C 101.42 C MP 0C 3.8C 3) Harmful to plants & animal Uses  Source of D 2  Moderator in nuclear reactors (controls fast moving neutrons)  Disinfectant Hydrogen Peroxide (H2O2) 1) 1st prepared by J.L.Thenard 2) Action of dil. H SO and Barium Peroxide 24 BaO2.8H2O  H2SO4  BaSO4  H2O2  8H2O Thenard process 3) White ppt of BaSO4 can be removed by filtration 4) About 5% H2O2 is obtained 5) Anhydrous BaSO cannot be used because it forms a layer over BaO to reduce the reaction rate 42 Other Preparation Methods Electrolysis Cold solution of 50% H SO is electrolised 24 2H2SO4  2H  2HSO4 Anode : 2HSO4  H2S2O8  2e Cathode: 2H  2e  H2 Peroxodisulphuric acid, H2S2O8  is hydrolised to get H2O2 H2S2O8  H2O  H2SO4  H2SO5 ( H2SO5 – Peroxomonosulphuric acid) H2SO5  H2O  H2SO4  H2O2 18

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) Merck’s Process: Calculated amount of Na O is gradully added to ice cold dil. H SO (20–80%) 22 24 Na2O2  H2SO4  Na2SO4  H2O2 Industrial Oxidation and reduction of 2-ethylanthraquinol OH O C2H5 C2H5 H2/Pd + H2O2 O2 OH O 2-ethylanthraquinol 2-ethylanthraquinone Physical Properties  Pale blue liquid in pure form  More dense and viscous than water (more H2 bonds)  Smell like HNO3  Completely miscible in water, alcohol and ether Structure  Non planar, non-linear  Open book like  O in SP3 hybridisation 2 H Dihedral/ inter plannar O angle : solid - 90.2o Liquid - 111.5o O H Kingzett structure H O O OH Baeyer's structure Chemical Properites H 1) Stability HO • Highly unstable • due to –1 O.S of O 2 19

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) • Readily decomposes to water and nascent oxygen • Accelerated by heat, dust, metal pieces, light, rough surface, etc H2O2  H2O  O • Preservatives: Glycerol, Urea, Acetanilide, H3PO4, etc C6H5.NH.COCH3  • Kept in wax coated plastic bottles • Alkaline oxides present in glass may  decomposition Acidic Nature  Dibasic acid  Give 2 H+ ions 2NaOH  H2O2  Na2O2  H2O H2O2  2H  O22 Oxidising & Reducing Nature  Can act as both  both in acidic & basic media  Due to –1 O.S. of O2 As an oxidiser: In acidic med: H2O2  2H  2e  2H2O In basic med: H2O2  2e  2OH As a reducer: In acidic med: H2O2  2H  2e  O2 In basic med: H2O2  2OH  2H2O  2e  O2 Redn Oxdn As As Reducer Oxidiser H2O/OH- H2O2 O2 0 -2 -1 H2O acidic Only O2 acidic H2O + O2 basic OH basic 20

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) Oxidiser: 1) Pb  4H2O2  PbSO4  4H2O 2) 2FeSO4  H2SO4 H2O2  Fe SO4 3  2H2O 3) 2KI  H2SO4 H2O2  K2SO4  2H2O  I2 4) 2K4 Fe CN6 4  2HCl H2O2  2K3 Fe CN 6 3  2KCl  2H2O 5) Mn2  H2O2  Mn4  2OH 6) Fe2  H2O2  Fe3  2OH Reducer: 1) 2KMnO4  3H2SO4 H2O2  K2SO4  2MnSO4  8H2O  5O2 2) Cl2  H2O2  2HCl  O2 3) I2  H2O2 OH 2I  2H2O  O2 7 4) 2MnO4  3H2O2  2MnO2  3O2  2H2O  2OH Bleaching Property • Can produce Nascent O2 • Used to bleach hair, feather, silk, wool etc Uses of H O 22 1) Bleaching agent for delicate materials (silk, wool, hair, feather, etc) 2) Antiseptic 3) Manufacture of chemicals like sodium perborate Per carbonate, etc - in high quality detergents 4) Synthesis of pharmaceuticals , food products like tartaric acid etc. 5) To control air pollution (restore aerobic condition in sewage) 6) 93% H O – Oxidant for Rocket fuel 22 H2O2  N2H4  (Hydrazine) Test for H O 22 1) Perchromic acid test Treated with acidified Ti salt solution – Yellow/Orange Ti4  H2O2  2H2O2  H2TiO4  4H 21

Brilliant STUDY CENTRE Residential Lecture Note (Chemistry) 2) Blue colour with starch solution 3) Perchromic acid Test dil.soln. of HO is shaken with acidified soln. of chromium salt  Blue colour [CrO ] 22 5 Concentration of H2O2  Expressed as volume strength  Represents the volume of O liberated from unit volume of H O at NTP. 2 22 Eg: 10 V, 20 V, 30 V etc. 10 V means – 1 ml H O liberates 10 ml O 2 22 (100 V H2O2 – Perhydrol) Relations for problem solving Normality = Molarity × n fact (For H O n factor = 2) 22 2H2O  2H2O2  O2 ie, diff . O.S. of O2  2, n factor n Molarity = vol.in L Vol. str Molarity = 11.2 Vol. str 1.7 Strength = 5.6 % Strength = Vol. str 17 56 Degree of Hardness: ppm of compound  100 If ppm of compound is given, ppm in terms of CaCO m.mass of compound 3 22