Hydrogen

Hydrogen INTRODUCTION Hydrogen is a lightest gas and lightest element of periodic table and its contain 1e, 1p and zero neutron. Lightest metal – Li * Lightest non metal – H * * * * Electronic Configuration – 1s1 Discovery of H-atom :  Discovered by "Covendish"  "Inflamable" air Term Hydrogen given by "Lavoisier" (Father of chemistry) Hydrogen is called hydrogen because maximum quantity of Hydrogen is used in preparation of H2O. Relative abundance : Hydrogen is most abundent element in the universe, i.e. 70% of the universe total mass. Hydrogen is highly reactive element as single atomic form but less reactive in their molecular state. Due to their high Bond energy. with respect to all diatomic (Homo atomic, Heteroatomic) molecule, hydrogen contain maximum bond energy (exception HF) Due to their small size of atom, H2 contain high bond energy. Method of preparation By 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) 1 Hydrogen By alkalies : Only (Be, Zn, Al, Sn, Pb) (Amphoteric (iii) Steam : The temperature of steam is more than metal) react with boiling NaOH or KOH they evolve 100°C. This form of water is used for very less H2. reactive metals like Fe, Cd, Co, Ni, Sn, Pb. Zn + 2NaOH  Na2ZnO2 + H2 (sodium zincate) 2Al + 2NaOH + 2H2O  NaAlO2 + 3H2 (sodium meta aluminate) (i) Cold water With highly reactive metals. (ii) Hot water With reactive metals (iii) Steam With less reactive metals. Sn + 2NaOH + H2O Na2SnO3 + 2H2 (sodium stannate) Pb + 2NaOH + H2O Na2PbO3 + 2H2 (sodium plumbate) Be + 2NaOH Na2BeO2 + H2 (sodium beryliate) Ex.1 Element which does not reach with NaOH. (i) Mg (ii) Be (iii)Al (iv) Zn (1) 1,3 (2) 1, 2, 3 (3) 1, 4 (4) 1, 3, 5 Sol. Ans. (1) Ex.2 Element which give H2 gas with caustic soda (NaOH). Ex.3 Which process does not form H2 gas. (1) Zn + ice cold H2O (2) Zn + H2SO4 (3) Na + ice cold H2O (4) Mg + Hot H2O Sol. Ans. (1) On Ionic hydride : Whenever ionic hydride reacts with water then form H2. CaH2 + 2H2O Ca(OH)2 + H2 (Hydrolith) Method to prepare pure hydrogen (i) Electrolysis of water : To prepare pure hydrogen we use impure water (i.e. having 15-20% solution of alkali or acid)    4H2O  4H+ + 4OH– at cathode 4H+ + 4e–  2H2 Sol. Ans. (2) at anode 4OH–  2H2O + O2 + 4e– From water : All the metals which are placed above The SO4–2 or K+ ion present in acid or alkali does than H2 when react with water the evolve H2. not move towards anode or cathode as their Zn + H2O ZnO + H2 discharge potential is higher than of OH– ions or H+ Three type of water is used ions respectively. (i) Cold water : The temperature of cold water is 7 to (ii) By reaction of Magnesium with dilute H2SO4 : 25°C this water is used for highly reactive metals. Mg + H2SO4  MgSO4 + H2 Such as Li, K, Ba, Sr, Ca, Na, means alkali metals (iii) By reaction of NaH with water : of alkalic earth metals. NaH + H2O  NaOH + H2 The reaction with alkali metals are vigorous to (iv) Uyeno method : This method is used for military minimum the rate of reaction these metals are used purpose. in the form of amalgam. 2Al + 2KOH + 2H2O  2KAlO2 + 3H2 2Na(Hg) + H2O 2NaOH + H2 (Potassium meta aluminate) (ii) Hot water : The temperature of hot water is 25°C Note : By this reaction we can prepare H2 in a rapid to 90°C. This water is used for reactive metals, manner. such as Mg, Al, Mn, Zn, Cr. (1) Zn (2) Al (3) Na (4) Ag 2 Hydrogen Commercial or industrial method to prepare H2 Water gas is mixed with twice the volume of steam (i) and passed over a mixture of ferric oxide and Lane's process : In this process, steam is passed over hot iron. Iron decomposes steam with the formation of magnetic oxide (Fe3O4) and hydrogen. The temperature of iron is maintained between 550 to 800°C. This reaction is termed gassing reaction and time alloted for this reaction is about 10 minutes. chromium oxide heated to 500°C. The mixture acts as a catalyst and helps in the conversion of carbon monoxide to carbon dioxide.  CO + 2H 2 2 3Fe + 4H2O  Fe3O4 + 4H2  Gassing Steam Magnetic oxide Iron is regenerated by reducing magnetic oxide with water gas (CO + H2). This reaction is called vivifaction and time alloted for this reaction is about 20 minutes. CO2 dissolves in water under pressure. The mixture of CO2 and H2 is passed through water under the pressure of 25 – 30 atmospheres. CO 2 dissolves completely in water. Traces of CO present in hydrogen are removed by passing the gas through ammonical cuprous solution under a pressure of 200 This iron is again used for decomposition of steam. In order to make the process contiunuous, the above two reactions are carried out alternatively using two or more furnaces. (ii) Bosch's process : The maximum quantity of commercial hydrogen is obtained by the use of this method. Water gas is produced first by passing steam over hot coke at 1000°C. The temperature is not allowed to fall below 1000°C. atmospheres. The hydrogen manufactured by this method is utilized for the synthesis of ammonia in which CO acts as a poison for the catalyst. To make hydrogen completely free from CO, it is passed over nickel catalyst then all CO present is converted into methane. (iii) From Natural gas : CnH2n+2 + nH2O nCO + (2n + 1)H2 3 Hydrogen Ex.4 Acid used in formation of H2 gas ? (1) Concentrated H2SO4 (2) Dilute H3PO4 (3) Dilute H2CO3 (4) Dilute HCl Sol. Ans. (4) Ex.5 Which of following reaction do not form H2 ? (1) Fe + H2SO4 (2) Sn + H2SO4 (3) Cu + H2SO4 (4) Zn + H2SO4 Sol. Ans. (3) Ex.6 What happen when NaH is dissolved in water (solvent) ? (1) NaH Na+ + H– (2) (i) (ii) (iii) (iv) 3H2 + N2 2NH3 (Haber Process) H2 + X2 2HX CH2 = CH2 + H2 CH3 – CH3 Vegetable oil unsaturated fats Vagetable ghee (Vanaspati ghee) saturated fats. Uses 1. Hydrogenation of vegetable oil to form solid fats i.e. vanespati ghee. 2. In the oxyhydrogen torch and atomic hydrogen torch for welding process. 3. In liquid form as a rocket fuel. 4. In aeroplanes and in balloons mixture of Hydrogen & Helium is used as fuel [15% H2 + 85% He] ISOTOPIC EFFECT (3) HO + Na  NaOH * Effect which can change physical & chemical properties of isotopes is called isotopic effect. Sol. Ans. (2) * By isotopic effect, maximum change occur in physical Ex.7 Species or ion which doesnot exist in nature. property of isotopes but minimum change occur in (1) H+ (2) H3O+ (3) H2+ (4) 1,3 both chemical property of isotopes. Sol. Ans. (4) Physical property : melting point, boiling point, H+ ion doesnot exist in nature, because H+ is without density etc. e– species of size of H+ ions is negligible. Chemical property : Rate of chemical reaction. + H2 does not exist, because its bond order is 0.5. * Isotopic effect is found only in Hydrogen isotope because maximum mass number difference present Ex.8 Ion which is not present in dilute HCl. + + – in hydrogen isotopes. (1) H (2) H3O (3) Cl (4) HCl Sol. Ans. (1) N14 7N15  O16 8O17 8O18   7 8 – * * * * Hydrogen is a lightest colourless, odourless and tasteless gas. It is sparingly soluble in water. It is Note : Application of isotopes is not isotopic effect inflammable and less reactive gas. (Except H) Its freezing point (– 259.20C) and boiling point (i) CO60 in cancer treatment. (–2520C) are very low, indicating less intermolecular (ii) Iodine in thyroid gland treatment. attraction. Due to low melting point, liquid hydrogen Example of isotopic effect : is used as a cryogenic fluid (to produce low (i) CH4 + Cl2 CH3Cl + HCl (fast) temperature). (ii) CD4 + Cl2 CD3Cl + DCl (slow) H – H bond energy [ 104 Kcal mol–1] and 436 KJ Bond energy of C – D > C – H mol–1 H – H bond length [ 74 pm] so hydrogen is less  reactive and require high temperature for reaction 4 Hydrogen ISOTOPES OF HYDROGEN Property Protium or Deuterium or ordinary hydrogen heavy hydrogen Atomic number 1 1 1 Mass number 1 2 3 Exact atomic mass 1.008123 2.0142 3.0170 Symbol Molecular formula Tritium or or H2 D2 T2 1 1 1 the nucelus Nil 1 2 No. of electron 1 1 1 Electronic configu. 1s1 1s 1 1s1 Relative abundance 99.984% 0.016% 10–15 % Stability Stable Stable Unstable (Radioactive) No. of protons in the nucleus No. of neutrons in Physical contants 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 B.E. (H—H) 436.0 KJ mol–1 443.3 KJ mol–1 446.9 KJ mol–1 Heat of fusion & vaporisation Minimum H D–D > T–T Stability of Isotopes on the basis of reaction with Cl2. T–T > D–D > P–P Stability of Isotopes according to bond energy. T–T > D–D > P–P On the basis of their physical properties. T–T > D–D > P–P Position of hydrogen in periodic table Ex.10 Hydrogen can be placed : Position of H is not fixed in Periodic Table because (1) IA (2) IVA properties of hydrogen are similar with different (3) VIIA (4) both (1) and (3) groups i.e. IA,VIIA etc. Ans. (4) Normally hydrogen is placed in IA group because of properties (Valence shell electronic Ex.9 Normally hydrogen placed in configuration) is similar with I A group element (1) IA (2) IVA (3) VIIA (4) All of these Sol. Ans. (1) 5 Hydrogen Properties of hydrogen similar with IA group : Hydrogen IA * Oxidation state +1 (H+) +1(M+) * Valence shell e– configuration ns1 ns1 * Electron releasing tendency (H e– + H+) (M e– + M+) * H is strong reducing agent like Ist A group elements but reduce only below element. (In ECS) Properties of hydrogen with VIIA group : H * Oxidation state 1 (H–) Hydride (NaH) –1(X–) (NaX) Halide * Diatomic nature H2 X2 * Ionisation polential of H gas similar with halogen. * In electrolysis of metals halides and metal hydrides from diatomic gas, both halogen and hydrogen will liberate at anode. 2H– 2e– + H2 and Properties of hydrogen with IVA group : Both hydrogen and IVA group elements have half filled valence shell. H  1s1 or ns1 C  1s2 2s2 2p2 or ns2 np2 (i) VIIth A Half filled Atomic hydrogen (H) : Atomic hydrogen are also classified in three categories - 2X–  2e– + X2 Ex.11 Which of the following process form nascent H2 gas ? (1) C2H5OH (Acid) + Na (2) Al + NaOH (3) Zn + dilute H2SO4 (4) All of these Sol. Ans. (4) Adsorbed/Occluded hydrogens : Adsorbed H is hydrogen present at   Simple atomic hydrogen : H – H (H2)   2H * * * * Formed by dissociation of H2 gas and dissociation of H2 gas is an endothermic process. the outer surface of metal. An ideal condition for this is high temperature and Occlusion : The property of metal to adsorb any low pressure. gas is called occlusion. (ii) Molecular hydrogen : (Ortho & Para /Nuclear Nascent Hydrogen : isomers/Proton spin isomer) It is formed by specific chemical reaction i.e. Ortho & Para isomerism present in only diatomic formation of nascent hydrogen by base, acid and molecule with atomic number odd value (N2, H2, water F2, D2) but absent in O2 Zn + H2SO4 ZnSO4 + 2H H2 Ortho hydrogen : Molecular form of hydrogen with Nascent ( unstable) same spin of proton is called ortho hydrogen. Simple atomic hydrogen and nascent hydrogen are Total spin of proton good reducing agent.           FeCl3 + [H] FeCl2 + HCl   6 Para hydrogen : Molecular form of hydrogen with opposite spin of proton is called para hydrogen. * Total spin of proton = 0 * Internal energy : Normally internal energy of ortho hydrogen is more then the para hydrogen because * ortho hydrogen have same spin of proton or greater repulsion of proton. * Stability : At high temperature, ortho is more stable then para but at low temperature para is more stable than ortho. *       Hydrogen 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 / Interstitial hydrides : They are the compounds of d & f-block elements. Note : Pure para or 100% para may be possible. But 100% ortho is not possible because at high temperature molecular form of hydrogen is converted into atomic form. Reactivity of reducing property : Simple hydrogen 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. stochiometric in nature (i.e. having variable composition) > Nascent hydrogen > Adsorbed hydrogen > Molecular hydrogen ZrHx (x = 1.3 – 1.75) TiHx (x = 1.8 – 2) Ex.12 Which of the following process form Nascent H : (1) Al + NaOH (3) Na + C2H5OH (2) Zn + H2SO4 (4) All of the above * Ans. (4) All of these Metals of group 7,8,9 donot form any hydrides so this particular part of periodic table is known as hydride gap. (3) Covalent/Molecules hydrides 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. 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 non-conductor of electricity. Nomenclature – element + Suffix (ane) PH3 Phosphane LiH, NaH, KH, RbH, CsH, CaH2, SrH2, BaH2 NH3 Azane BeH2, MgH2 are covalent polymeric hydride. H2O Oxidane 7 Hydrogen These hydrides are again divides into 3 categories. (a) Electron deficient hydrides : * (i) Water is considered as most convenient solvent. Because its dielectric constant is high. 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. (ii) (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. 81 and it is a polar molecule. Due to these properties salts are highly ionised in water. The solubility of ionic compounds in water is also due to liberation of a large amount of hydration energy due to interaction between the ions of solute and the polar water molecules. (iii) Water is not good solvent for covalent compounds because in this case less amount of energy is released which can not overcome even the weak van der Waals' force of attraction of the covalent compound what to say of breaking of hydrogen bonds in water. (iv) Solubility of some covalent compounds. Ex. alcohols, acids, amines, carbohydrates etc. in water is due to In these hydrides lone pair are present on central their capability of forming hydrogen bonding with atom which can be given to others. So they are called water. electron rich hydrides. For pure water pH = 7 etc. Ex. [H+] = [OH] = 10–7 at 250C Water (H2O) Water act both as oxidising and reducing agent. Na + H2O  NaOH + Kw = 10–14 (v) Reaction : H2 C + H2O  Cl2 + H2O  [CO + H2] HCl + HOCl water gas Hypchlorous acid 2NaOH + H2 Reducing agent Oxidising agent 2F2 + 2H2O  4HF + O2 2Na + 2H2O  3F2 + 3H2O  6HF + O3 2Cl2 + 2H2O   4HCl + O2 Oxidising agent Reducing agent (vi) Hydrolysis :   acid + alcohol Ester + H2O  (vii) Reaction with carbides : (i) Pure water is colour less, test less and odour less. 0 By reaction with H2O & carbides form of difference type of hydrocarbon (Alkane, Alkyne, Alkene). 0 (ii) It freezes at 0 C and boil at 100 C (iii) Density of water is 1 at 00C (i) (iv) Density of ice < density of H2O ( 40C maximum) (ii) Al4C3  [4Al+3]+12 + C3H12(unstable)  3CH4 (v) Volume of ice > H2O (vi) Pure water is a bad conductor of electricity due to very low degree of ionisation. (vii) In absance of HydrogenBond boiling point of H2O about – 100°C.     C3–12   (iii) Silicon caibide will not react with H2O because of its diamond like structure. 8 Hydrogen (viii) Reaction with Non-metal oxide : Non-metal oxide + H2O  Oxyacid. N2O5 + H2O  2HNO3 Water from rivers, springs or even wells contains a certain amount of dissolved mineral substances. Water containing soluble calcium and magnesium salts such as bicarbonates, chlorides, sulphates is termed hard water and if these salts are absent, the SO3 + H2O  H2SO4 (ix) Reaction with Metal oxide : Metal oxide + H2O  Hydroxide Na2O + H2O  2NaOH water is called soft water. Test of water : Hard water is one which does not easily lathers with soap (Na or K salts of higher fatty acids). This is due to the formation of precipitate of Ca or Mg stearate while a sample of water which lathers easily with soap is called soft water. CuSO4 + H2O  Blue colour Structure of water : CaCl2 + 2C17H35COONa present in sodium stearate hard water (soap)  Ca(C17H35COO)2  + 2NaCl Calcium Stearate Note : Hard water is not always harmful for drinking purposes. However it is disadvantageous in the laundry work. Method for permanent Hardness : Temporary Hardness : Due to presence of Ca and Mg bicarbonate like Ca(HCO3)2, Mg(HCO3)2 Permanent Hardness : Due to presence of Ca and Mg Chlorides and Sulphates like CaCl2, MgSO4 etc. Removing Hardness from water : Method for temporary Hardness : (i) By Boiling (ii) By Clark's process [Using Ca(OH)2] CaO (s) + H2O Ca(OH)2 (quick lime) (Slaked lime) Note : Here Ca(OH)2 can not used as excess quantity because Ca(OH) 2 by absorbing CO2 further formation of Ca(HCO3)2. (i) By Na2CO3 (washing soda) Method for Both temporary as permanent hardness: (i) Lime and soda process : In this proces both Ca(OH)2 and Na2CO3 added together to hard water. (ii) By Ion exchange process : (A) Inorganic process (C) Calgon process (B) Organic process (A) Inorganic process : Permutit process : For this process used inorganic salt like hydrates of sodium & aluminium silicates. [Na2Al2Si2O8 . xH2O] this compound also called "Zeolite" Zeolite is a water softner & shape selective catalyst. 9 Hydrogen Formation by Na2CO3, Al2O3, SiO2 etc. This general formula of its – Na2Z here, Z = Al2Si2O8. x H2O In this process column chromatography always used. Na2Z + CaCl2 CaZ + 2NaCl (B) Organic Process : In organic process, always organic substance is used. D2O (Heavy water) Heavy water is deuterium oxide (D2O). It was discovered by Urey (1932). One part of D2O is present in about 6000 parts of H2O. Theoritically six different types of heavy water are possible in terms of three different isotopes of oxygen Ex. H–O16–D, H–O17–D, H – O 18– D and D–O16–D, D–O17–D, D–O18–D. Cation exchanger : exchange only hard cation. Ex. R – COO–H+ 2RCOO–H+ + Ca+2  (R – COO)2Ca  + 2H+ Anion exhanger : exchange only hard anion. Ex. R – NH2– OH– 2R – NH2– OH– + Cl– R – NH2 Cl–  + OH– Ex.13 Which of the following substance produce hardness in water. (1) CaCO3 (2) CaCl2 (3) Na2CO3 (4) Na2(HCO3)2 Sol. Ans. (2) Chemical property of H2O and D2O are same but rate of chemical reaction of H2O > D2O. because bond energy of O–D > O–H Like water but process is slow due to high bond energy. 2D2O  2D2 + O2 2Na + 2D2O  2NaOD + D2 Sodium deutroxide SO3 + D2O  D2SO 4 Heavy sulphuric acid Al4C3 + 12D2O 4Al(OD)3 + 2CD4 CaC2 + 2D2O Ca(OD)2 + C2D2 It is injurious to living organism and does not support life so well. It also retards the growth of living organism, plants and animals. Key Point Uses Ethylene diaminetetraacetic acid (EDTA) is a (i) It is used in production of heavy hydrogen, and versatile complexing agent hence it can remove deutero compounds, as a tracer compound and as hardness of water by forming stable complexes with a moderator in atomic reactors. metal ions. It is also used for estimating the hardness (ii) Used as a Moderator of water, volumetrically. H2O2 (Hydrogen Peroxide) (C) Calgon Process : Calgon is the trade name of sodium hexameta-phosphate, Na2(Na4(PO3)6]. The Ca2+ and Mg2+ ions present in hard water react with (i) Auto oxidation of 2 butyl anthraquinol ( cyclic calgon to form complex anions, which are very process) : inactive and do not form precipitate with soap. Na2[Na4(PO3)6] + 2Ca2+  Na2[Ca2(PO3)6] + 4Na+     soluble complex 10 Hydrogen (ii) Oxidation of isopropyl alcohol : The vapour density as determined by Victor (iii) Electrolytic Process : Used 50% H2SO 4 in electrolytic cell using Pt as anode graphite as cathode. 2H2SO4 2H+ + 2HSO4 At Cathode 2H+ + 2e– H2  At Anode 2HSO4– H2S2O8 + 2e–| Meyer method at 90°C is 17. Hence, the molecular mass of H2O2 is 34. Two formulae have been suggested for hydrogen peroxide. Peroxo disulphhuric acid H2S2O8 + H2O  H2SO4 + H2SO5 + H2O  H2SO4 H2SO 5 + H2O2 Note : Now a day use 50% (NH4)2 SO4 with 50% H2SO4. (i) Pure H2O2 is colour less, odourless liquid and impure with bluish layer. distance is 1.48Å and X-ray measurements shows what in hydrogen peroxide, O–O bond distance is (ii) It has more Hydrogen bonding then H2O, So order 1.46 + 0.03Å. The value of dipole moment of H2O2 of boiling point. is 2.1 D. This suggests that all the four atoms do not lie in the same plane. The molecule can be pictured (iii) It is soluble in H2O, alcohol and ether as lying on the spine of a book open to an angle of (iv) It has bitter test and harmful for skin 111°. The hydrogen atoms are present one on each (v) It is a dibasic weak acid cover and H–O bonds making angles of 94° with (vi) It has a oxidising as well as reducing property the O–O bond as shown in fig. The bond distance between O–H is 0.97Å. (vii) H2O2 easily decompose in presence of light and Precautions : temperature, So H2O2 always kep in dark bottles (i) H2O2 can not be stored in simple glass bottles since and kept at cool places. rough surface of glass [alkali oxides present in it] (viii) 30% solution of H2O2 is called Perhydrol. excited by light and decomposed H2O2. So the H2O2 usually stored in coloured, paraffin wax coated, plastic bottle. (i) It is unstable in nature decompose on standing and (ii) Always with H2O2 add small quantity of inhibitor or heating. It is an example of auto oxidation-reduction negative catalyst to stay decomposition of H2O2. like H3PO4, acetanilides etc. Reaction ; H2O2  H2O + O Uses Note : Nascent oxygen working as colourless agent (i) Bleaching agent   (ii) Decomposition of H2O2 ; 2H2O2   2H2O + O2 (ii) Hair dying (iii) H O + N2H4 as Rocket propellent Note : This is retarded by R–OH, acetenilide glycerol (iv) H2O2 as oxidant and reductant 2 2 acelerates by Pt, Au, Ag, MnO2 (v) Antiseptic 11