Hydrogen and its compounds

This file contains all the information about hydrogen and its compounds.

1. Pankaj Bahrani

2. HYDROGEN

3. Introduction Discovered by Henry Cavendish and named it as Inflammable element. Lavoisier named it hydrogen (Hydro= Water Gene=producer) Lightest Element in Periodic Table. Most Abundant in Universe. 9 th most abundant on Earth’s crust. Order of Abundance: Universe > Sun > Earth Due to more gravitational pull of Sun , atomic form of hydrogen is available but on Earth it is present in molecular form.

4. It is the s implest element with electronic configuration of 1s 1 having only one proton and one electron (and no neutrons in its most common isotope). Hydrogen is most reactive in atomic form but less reactive in molecular form because of greater extent of overlapping of 1s-1s orbitals. Hydrogen is the fuel for reactions of the Sun and other stars (fusion reactions).. All stars are essentially large masses of hydrogen gas that produce enormous amounts of energy through the fusion of hydrogen atoms at their dense cores. In smaller stars, hydrogen atoms collided and fused to form helium and other light elements like nitrogen and carbon(essential for life). Introduction

5. Isotopes of Hydrogen Hydrogen  (H) has 3 naturally occurring  isotopes , sometimes denoted  1 H,  2 H, and  3 H. The first two of these are stable, while  3 H has a  half-life  of 12.32 years. 

6. Properties of Isotopes

7. Isotopic Effect The Change in properties of isotopes due to difference in mass is called Isotopic effect. Large change in properties is seen in the isotopes of hydrogen due to large differences in the mass. In other elements the mass difference is not so large so less changes are seen. Hydrogen Isotopes are used in study of reaction rates. This is also referred as Kinetic Isotopic effect. Br 2  +  CH 4  → HBr + CH 3 Br (Reaction Fast as C-H Bond breaking is involved) Br 2  +  CD 4  → DBr + CD 3 Br (Reaction Slow as C-D Bond breaking is involved)

8. Why do we have Unique Position of Hydrogen Unique Position

9. Position In Periodic Table The placement of elements in the periodic table is based on their  electronic configuration . This structure is similar to that of alkali metals (ns 1 ) which have 1 electron in their outermost shell. It can attain the noble gas configuration of helium, by accepting one electron. This character is very much similar to that of halogen family (ns 2  np 5 ) which are also short of one electron to complete the octet of electrons in their shells.

10. Electronic Configuration : contains one Electron In the outermost shell. Electropositive : Like Alkali metals, Hydrogen also looses its one electron to form hydrogen ion, i.e., H + Combination With Electronegative Elements : Like Alkali metals Hydrogen also combines with electronegative elements such as oxygen, sulphur, halogen. Oxidation State : Hydrogen also shows the oxidation state of +1 in its compound. Reducing Character : Like Alkali metals Hydrogen also act as a strong reducing agent. Resemblance With Alkali Metals

11. Electronic Configuration : All the Halogen wants one electron to complete its octet, this property is shown by Hydrogen also. Electronegative Character : Halogens have a strong tendency to gain electron to form halide, Hydrogen also shows same tendency. Ionization Enthalpy : Ionization Enthalpy of Hydrogen is quite comparable with those of the Halogen. Oxidation State : Just Like halogen Hydrogen shows the oxidation state of -1. Combination With Metals : Hydrogen combines with the metals in the same way as the halogens combine. Resemblance With Halogen

12. Nature Of oxides : Hydrogen forms oxides that are neutral unlike alkali metals & halogen. Size Of ion : The Size of ion is not comparable with the size of the ions of alkali metals & halogen. Differences from Halogen & Alkali metals

13. Classification Of Hydrogen

14. Lab Preparation : 1. Reaction o f dilute acid with granulated impure zinc Zn + H 2 SO 4 → Zn SO 4 + H 2 Preparation Of Hydrogen

15. Lab Preparation : 2. Reaction o f NaOH with metals like Pb, Be, Zn , Al and Sn. Zinc reacts with NaOH to form sodium zincate with the evolution of hydrogen gas. Zn + 2NaOH → Na 2 ZnO 2 + H 2 Preparation Of Hydrogen

16. Commercial Preparation 1. Electrolysis of acidified water/ alkalinated water using platinum electrodes. Electrolysis 2H 2 O (l) → 2 H 2 (g) + O 2 Preparation Of Hydrogen Water is acidified by adding some amount of H 2 SO 4 OR Water is alkalinated by adding some amount of Ba(OH) 2

17. Commercial Preparation 2.Electrolysis Of Brine solution Electrolysis Na + + Cl - + H 2 O(l) → 2NaOH + H 2 + Cl 2 Preparation Of Hydrogen Cell used for electrolysis: Nelson Cell Caster Kellner Cell

18. Commercial Preparation 3.Lane’s Process: In the steam-iron process the iron oxidizes and has to be replaced with fresh metal. 3Fe+ 4H 2 O → Fe 3 O 4 + 4H 2 Lane hydrogen producer the iron is  reduced  with water gas back to its metallic condition, after which the process restarts. Fe 3 O 4 + 4CO → 3Fe + 4CO 2 Preparation Of Hydrogen

19. Commercial Preparation 4. Reaction of steam with Hydrocarbons in the presence of Catalysts to produce water gas. If nitrogen is present it forms producer gas CH 4 + H 2 O → CO + H 2 (Co + H 2 ) → Water Gas or Syngas (CO + N 2 ) → Producer Gas Next Step is Water Gas Shift Reaction CO + H 2 + H 2 O (g) → CO 2 + 2 H 2 Preparation Of Hydrogen

20. Physical Properties : Colorless Tasteless Odorless Lightest substance. Slightly soluble in water. Can be liquefied under low temperature & high pressure . Low Melting and Boiling Point Properties Of Dihydrogen

21. Chemical Properties : Neutral In nature Less Reactive in molecular form Reaction With Metal: formation of ionic hydrides. 2Na + H 2 → 2NaH Reaction With Oxygen: formation of Water 2 H 2 + O 2 → 2 H 2 O Properties Of Dihydrogen

22. Chemical Properties : Reaction With Nonmetals Halogen H 2 + X 2 → 2HX(X=F, Cl, Br, I) Dinitrogen N 2 + 3H 2 → 2NH 3 Sulphur H 2 + S → H 2 S Carbon C + 2H 2 → CH 4 Properties Of Dihydrogen

23. Chemical Properties : Hydrogenation of Veg. Oil Unsaturated hydrocarbons (Veg. Oil) add dihydrogen in presence of catalysts (like Ni, Pt, Pd) to form saturated hydrocarbons(Veg. Ghee) Properties Of Dihydrogen

24. Hydrogenation of Vegetable Oil to solid fats. Manufacturing of chemicals ( methanol ,ammonia , hydrocarbons) Manufacture Of metal Hydrides . In Metallurgy to reduce heavy metals. Used as rocket propellent (liquid hydrogen + liquid oxygen) Used in balloons (15% H 2 + 85% He) Nuclear weapons. Use s Of Dihydrogen

25. Hydrides Compounds of hydrogen with other elements are called hydrides. Hydrides are classified in three types based on bonding present: Ionic or Salt like hydrides Covalent or Molecular hydrides Metallic or Interstitial Hydrides

26. Hydrides in Periodic Table The elements that do not form hydrides are indicated as hydride gap in periodic table.(Complete Group 7,8,9 and some other transition metals in different groups)

27. Ionic or Saline Hydrides They are formed when hydrogen molecule reacts with highly electropositive s-block elements (Alkali Metals and Alkaline Earth Metals). In solid-state, the ionic hydrides are crystalline, non-conducting and non-volatile. However, in a liquid state, they conduct electricity. Ionic hydrides on electrolysis liberate hydrogen gas at the anode.  Saline or ionic hydrides does not dissolve in conventional solvents and they are mostly used as bases or reducing reagents in organic synthesis. Example of Ionic Hydrides:  NaH, KH, CaH 2 These contain hydrogen as the negatively charged (H – ) ion

28. Covalent or Molecular Hydrides Covalent hydrides are formed when hydrogen reacts with other similar electronegative elements like Si, C, etc.  The most common examples are CH 4  and NH 3 . In general, compounds that are formed when hydrogen is reacted with non-metals are called covalent hydrides. The compound shares a covalent bond and are either volatile or non-volatile compounds.  Covalent hydrides are also either liquids or gases. Covalent Hydrides:  SiH 4   (silane )

29. Covalent or Molecular Hydrides

30. Metallic or Interstitial Hydrides A hydrogen compound that forms a bond with another metal element is classified as a metal hydride. Metal hydrides are also known as interstitial hydrides. They are formed when hydrogen molecule reacts with the d- and  f-block elements . The bond is mostly covalent type but sometimes the hydrides are formed with ionic bonds. These are usually formed by transition metals and are mostly non-stoichiometric, hard, high melting and boiling points. They do conduct heat and electricity but not to the extent of their parent metals. Example of Metallic Hydrides:  TiH 1.2-1.8

31. Metallic or Interstitial Hydrides

32. WATER

33. Properties of water Chemical Formula: H 2 O Appearance: Water is colorless, odorless and tasteless liquid in its natural state. Boiling Point: 100 C. Freezing Point: 0 C.. Density: One unique property of water is that in the sold state, it is less dense. Up to 4°C water’s density does increase on cooling. But after that point water becomes less dense. This is why ice floats in water, Viscosity: Water has high viscosity due to very strong intermolecular interactions Solvency: Water is an excellent polar solvent. In fact, it is known as a Universal Solvent. 

34. Properties of water Amphoteric Nature: Water is neither acidic or basic it acts as both. This is because of its ability to both donate and accept protons. For acids stronger than water it acts as a base. These two following reactions show this amphoteric nature. H 2 O (l) + HCl ( aq ) ⇌ H 3 O + +  Cl –  H 2 O (l) + NH 3  ( aq ) ⇌ NH 4 +  + OH – Hydrolysis Reaction: Water has a very high dielectric constant. This results in it having a strong hydrating tendency. Water has strong reactions with ions of salts and creates hydrating shells around them. SiCl4 + 2H2O → SiO2 + 4HCl Redox Reactions: Water is a great source to obtain dihydrogen since it can be reduced by reacting it with highly electropositive metals such as Sodium. H2O + Na → 2NaOH  + H2

35. ICE The structure of the molecules of water in its frozen form i.e. ice is very unique. It forms a Lattice Structure that does not generally occur naturally in any other substance other than ice. When water reaches its freezing point its atoms rearrange themselves in a very specific three-dimensional pattern. The oxygen atom is surrounded by four hydrogen atoms. Two of these form O-H bonds normally seen in water molecules. The other two form a hydrogen bond. This very special hexagonal shape is what gives ice the unique property of being less dense than water. Since in the structure of ice there are empty spaces between the hexagonal structure, its density is less than that of water in its liquid state. This is why ice floats on water.

36. Structure of Ice

37. Hard water and Soft water

38. Hard water and Soft water

39. Hard water and Soft water

40. Why softening of Hard Water is essential ? Reduction of soap consumption Lowered cost in the maintenance of plumbing Improved taste in foods prepared A must for industrial supplies 4 RGU IIIT NUZVID Courtesy: lenntech.com Courtesy: ndsu.edu basin

41. Removal of temporary hardness (Boiling Method) Temporary hardness is due to carbonates and bicarbonates of calcium and magnesium. It Can be removed either by boiling 𝐶𝑎𝐶𝑂 3 is slightly soluble in water. So it usually exists in water as a bicarbonate. Boiling will lead to the precipitation of 𝐶𝑎𝐶𝑂 3 and release of 𝐶𝑂 2 . 𝐶𝑎(𝐻𝐶𝑂 3 ) 2 (On Boiling) → 𝐶𝑎𝐶𝑂 3 (s) + 𝐶𝑂 2 (g) + 𝐻 2 O Mg(𝐻𝐶𝑂 3 ) 2 (On Boiling) → Mg 𝐶𝑂 3 (s) + 𝐶𝑂 2 (g) + 𝐻 2 O 𝐶𝑎𝐶𝑂 3 and MgCO 3 is precipitated.

42. Removal of temporary hardness (Clark’s Process) In Clark’s method of water softening, hard water is treated with Ca(OH) 2  (slaked lime). Water softening by Clarke’s process uses calcium hydroxide (lime). It removes temporary hardness. Ca(HCO 3 ​) 2 ​+Ca(OH) 2 ​→2CaCO 3 ​+2H 2 ​O. This method involves the addition of slaked lime to water either in solid or in liquid form. This results in the conversion of soluble bicarbonates to insoluble  carbonates .

43. Removal of Permanent hardness (Washing Soda) Sodium carbonate, Na 2 CO 3 , is also known as washing soda. It can soften water that has temporary hardness and it can soften water that has permanent hardness. Sodium carbonate is soluble in water and adds a large amount of carbonate  ions  to the water. These react with dissolved calcium and magnesium ions, forming a  precipitate  of their carbonates Ca 2+ ( aq ) + CO 3 2– ( aq ) → CaCO 3 (s) Mg 2+ ( aq ) + CO 3 2– ( aq ) → MgCO 3 (s) The calcium ions come from the hard water and the carbonate ions from the washing soda.

44. Removal of Permanent hardness (Calgon’s Process) Calgon method involves treatment of C algon (sodium hexametaphosphate, Na 6 P 6 O 18 ) to form complex anion, which keeps the Mg 2+ and Ca 2+ ions in solution Calgon ionizes to give a complex anion: (NaPO 3 ) 6 → 2Na + + [Na 4 P 6 O 18 ] 2- The addition of Calgon to hard water causes the calcium and magnesium ions of hard water to displace sodium ions from the anion of Calgon. Ca 2+ + [ Na 4 P 6 O 18 ] 2- → 2Na+ + [Ca Na 2 P 6 O 18 ] 2- Anion of calgon goes into solution This results in the removal of calcium and magnesium ions from hard water in the form of a complex with Calgon.

45. Removal of Permanent hardness ( Permutit or Zeolite Process) Zeolites are naturally occurring sodium aluminum silicates having different amounts of water of crystallization. They are represented as Na 2 O.Al 2 O 3 .xSiO 2 .yH 2 O where x and y varies from 2 to 10 and 2 t 6 respectively. They are produced synthetically as well. They have the property of exchanging their Na ions for hardness causing ions like Ca++  and  Mg++ The reactions taking place the softening process are as follows where Ze represents zeolite. Ca(HCO 3 ) 2 +Na 2 Ze→CaZe+2NaHCO 3 MgSO 4 +Na 2 Ze→MgZe+Na 2 SO 4 CaCl 2 +Na 2 Ze→CaZe+2NaCl The Ze mineral gets exhausted when all the Na+ are replaced by Ca++ and Mg++ ions. Now Ze can be regenerated by passing Nacl solution, CaZe+2NaCl→CaCl2+Na2Ze

46. Removal of Permanent hardness ( Permutit or Zeolite Process) Zeolite softening is carried out in large cylindrical tank as shown, holding Ze material on a perforated platform. The tank has two inlets for feeding raw water and passing saturated NaCl solution. There are two outlets for softened water and removing CaCl 2 ,MgCl 2 the wash water formed during the regeneratio n.

47. Removal of Permanent hardness (Ion Exchange Resins)

48. Removal of Permanent hardness (Ion Exchange Resins) An ion-exchange resin or ion-exchange polymer is a resin or polymer that acts as a medium for ion exchange. It is an insoluble matrix (or support structure) normally in the form of small (0.25–0.5 mm radius) microbeads The beads are typically porous, providing a large surface area on and inside them the trapping of ions occurs along with the accompanying release of other ions, and thus the process is called ion exchange. There are multiple types of ion-exchange resin. Most commercial resins are made of polystyrene sulfonate. Ion-exchange resins are widely used in water softening and water purification.

49. Removal of Permanent hardness (Ion Exchange Resins) In this application, ion-exchange resins are used to replace the magnesium and calcium ions found in hard water with sodium ions. When the resin is fresh, it contains sodium ions at its active sites. When in contact with a solution containing magnesium and calcium ions (but a low concentration of sodium ions), the magnesium and calcium ions preferentially migrate out of solution to the active sites on the resin, being replaced in solution by sodium ions. This process reaches equilibrium with a much lower concentration of magnesium and calcium ions in solution than was started with.

50. Removal of Permanent hardness (Ion Exchange Resins) The resin can be recharged by washing it with a solution containing a high concentration of sodium ions (e.g. it has large amounts of common salt (NaCl) dissolved in it). The calcium and magnesium ions migrate from the resin, being replaced by sodium ions from the solution until a new equilibrium is reached. The salt is used to recharge an ion-exchange resin, which itself is used to soften the water.

51. Heavy Water Deuterium is a stable isotope of hydrogen and Heavy Water (D 2 O) contains two atoms of Deuterium (D) and one atom of oxygen. This is also known as Deuterium Oxide. Ordinary water as obtained from most natural sources contains about one deuterium atom for every 6,760 ordinary hydrogen atoms and the residual water is thus enriched in deuterium content

52. Heavy Water

53. Heavy Water Methods of Preparation : Prolonged Electrolysis of water: On electrolysis of water, the water disassociates in H + and OH - while fractional part disassociates in D + and OD - ions. Due to higher mass D + and OD - have lower mobility and H 2 and O 2 releases from water leaving D 2 O in solution. Process is repeated 6 times.

54. Heavy Water Methods of Preparation : By Fractional Distillation At normal atmospheric pressure the boiling point of ordinary water and heavy water are 373K and 374.42K.So can be separated by fractional distillation of water. Generally fractionating column of 12 meters is used to isolate heavy water from ordinary water.

55. Heavy Water Methods of Preparation : By Fractional Distillation

56. Heavy Water Physical Properties: Colorless Odorless Tasteless Higher B.P , M.P. is seen due to marked difference in mass from ordinary water. Dielectric constant of heavy water is smaller than ordinary water therefore ionic compounds are slightly less soluble in heavy water.

57. Heavy Water

58. Heavy Water Chemical Properties: All chemical properties of heavy water are same as that of ordinary water only the rate of reaction is slow as the bond disassociation is slow and more energy consuming than ordinary water.

59. Heavy Water Uses: In tracer studies for organic reactions kinetic studies In tracer studies for biological and metabolic testing In atomic/nuclear reactors for slowing the speed of moving neutrons (as a moderator) in temperature control for nuclear reactors (as a coolant). In testing instruments like FTIR and NMR spectroscopes.

60. D 2 O as a Moderator and Coolant

61. Hydrogen Peroxide H y d r og e n Peroxide w as discovered by a French chemist J.L. Thenard in 1818. Hydrogen peroxide( H 2 O 2 ) has a open book like structure. H 2 O 2 has a none planar structure in which two H atoms are arranged in two directions almost perpendicular to each other and to the axis joining the two oxygen atoms. The O ─ O linkage is called peroxide linkage. In the solid phase, the dihedral angle is reduced to 90.2 degree from 111.5 degrees in the gas phase.

62. Hydrogen Peroxide Structure

63. Hydrogen Peroxide Methods of Preparation : The action of cold, dil. sulphuric acid on sodium peroxide. (Merck’s process) Hydrogen peroxide is prepared by adding sodium peroxide to ice cold dil. sulphuric acid. The addition is carried out slowly in small amounts with stirring. On upon cooling, crystals of Na 2 SO 4 . 10H 2 O separate out. The crystals of Na 2 SO 4 . 10H 2 O are decanted leaving behind solution of hydrogen peroxide Na 2 O 2 +H 2 SO 4 →Na 2 SO 4 +H 2 O 2

64. Hydrogen Peroxide Methods of Preparation : The action of cold, dil. sulphuric acid on barium peroxide. In this method, a paste of hydrated barium peroxide is prepared in ice cold water and is treated with about 20 % ice cold solution of sulphuric acid. BaO 2 .8H 2 O+H 2 SO 4 →BaSO 4 +H 2 O 2 +8H 2 O The white precipitate of BaSO 4 is removed by filtration leaving behind about 5 % solution of H 2 O 2

65. Hydrogen Peroxide Methods of Preparation : By the electrolysis of 50% sulphuric acid In this method, a 50 % solution of sulphuric acid is electrolyzed at h i gh c urr e nt d i n a n e l ec t ro l y t ic ce l l w h e n peroxodisulphuric acid is formed at the anode. The acid is drawn off from the cell and hydrolyzed with water to give H 2 O 2 . 2H 2 SO 4 →H 2 S 2 O 8 +H 2 H 2 S 2 O 8  + 2H 2 O → H 2 O 2  + 2H 2 SO 4

66. Hydrogen Peroxide Methods of Preparation : By 2-ethyl anthraquinone The method involves the following steps: 2 ethyl anthraquinone is dissolved in benzene and hydrogen gas is passed in the presence of palladium catalyst. The reduced product is dissolved in a mixture of benzene and cyclohexanol and upon passing air, it is oxidised back to 2 ethyl anthraquinone and H 2 O 2 is produced.

67. Hydrogen Peroxide Methods of Preparation : By 2-ethyl anthraquinone

68. Hydrogen Peroxide Physical Properties: Pure H 2 O 2 is a thick syrupy liquid which is colorless, odorless and bitter in taste. It is more viscous, less volatile and dense than water. Extent of H-Bonds more so higher B.P. It is a dibasic weak acid. Its melting point is 272.4K and boiling point is 358K at 68mm of Hg pressure. It is completely miscible with water, alcohol and ether in all proportions. 30% aqueous solution is called PERHYDROL.

69. Hydrogen Peroxide Chemical Properties: H 2 O 2 b ehaves as an oxidizing agent as well as reducing agent in both acidic and alkaline solution. Oxidizing action in acidic medium In the presence of an acid, H 2 O 2 can accept electrons and, thus acts as an oxidizing agent. ` 2Fe+2H + +H 2 O 2 →2Fe+2H 2 O 2 Reducing action in acidic medium HOCl +H 2 O 2 →H 3 O + +Cl - +O 2

70. Hydrogen Peroxide Chemical Properties: Oxidising action in basic medium 2Fe+H 2 O 2 →2Fe+2OH - Reducing action in basic medium I 2 +H 2 O 2 + 2OH - →2I - + 2H 2 O+O 2

71. Hydrogen Peroxide Uses: It is used in industry as a bleaching agent for textiles, paper, pulp, straw, leather, oils, fats etc. It is used as an antiseptic for washing wounds, teeth and ears under the name perhydrol. It is used as a mild disinfectant and a hair bleach. It is used in preparation of high quality detergents like perborates and percarbonates. It is used for restoring the color of lead paintings.

72. Hydrogen Peroxide It is used for the production of epoxides and polymers. It is used for the synthesis of hydroquinone, pharmaceuticals, food products . It is used as an antichlor in bleaching also for for preserving milk and wines. It is also used in environmental chemistry such as in pollution control treatment of domestic and industrial effluents, oxidation of cyanides and restoration of aerobic conditions to sewage waste.

73. Storage of H 2 O 2 The following precautions must be taken while storing H 2 O 2 : It must be kept in wax lined bottles because the rough glass surface causes its decomposition. It can also undergo photodecomposition so colored bottles used. A small amount of phosphoric acid, glycerol or acetanilide is generally added which retard the decomposition of H 2 O 2 . These are also called negative catalysts.

74. Storage of H 2 O 2