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CHAPTER 18

CHAPTER 18. Hydrogen, Oxygen, and Water. Hydrogen. Isolated by Cavendish by the reaction of acids with active metals Named by Lavoisier (hydrogen – water former) Thought to be the most abundant element in the universe.

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CHAPTER 18

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  1. CHAPTER 18 • Hydrogen, Oxygen, and Water

  2. Hydrogen • Isolated by Cavendish by the reaction of acids with active metals • Named by Lavoisier (hydrogen – water former) • Thought to be the most abundant element in the universe. • Found at ~0.53 ppm in earth’s atmosphere, and is the 9th most abundant element in the crust.

  3. H D T Isotopes of Hydrogen • Hydrogen isotopes are treated differently Hydrogen exhibits isotope effects. These isotope effects arise from the dramatic difference in masses of the isotopes.

  4. Hydrogen and the Hydrides • H2 can be made by the reaction of a metal with a nonoxidizing acid. Nitric acid, HNO3, is the strongest oxidizing acid. Sulfuric acid can also act as an oxidizer depending upon the metal. Commercially, hydrogen is prepared by the thermal cracking of hydrocarbons (preparation of gasoline and acetylene).

  5. Reactions of Hydrogen and the Hydrides • Hydrogen reacts with active metals to yield hydrides. • In general for IA metals In general for IIA metals In general for IIIA metals

  6. Reactions of Hydrogen and the Hydrides • Ionic hydrides are basic (alkaline). • H- reacts with water to produce H2 and OH–. Hydrogen reacts with nonmetals to produce covalent binary compounds.

  7. Reactions of Hydrogen and the Hydrides • Ionic or Covalent Character of Hydrides • Metal hydrides are ionic and basic. • The post transition metal hydrides tend to be mostly covalent (gases, liquids, and solids). • The H acts like a H– in their reactions. • Nonmetal “hydrides” are all covalent. • The VIA and VIIA compounds are acidic. • The VA compounds are (Lewis) bases. • The IVA compounds are neutral.

  8. Reactions of Hydrogen and the Hydrides • Metallic Hydrides • Metallic or Interstitial Hydrides are made with the lanthanide and actinide metals and certain d-transition metals. • These hydrides are nonstoichiometric compounds and their composition depends upon H2 pressure. • The properties of these hydrides depends upon their composition.

  9. Oxygen and the Oxides • Priestley discovered oxygen in 1774 (phlosgen), named by Lavoisier (acid former) Laboratory preparation Ozone is an allotropic form of oxygen. Both O2 and O3 are excellent UV absorbers. Ozone absorbs harmful UV light. This same UV light will convert O2 to O3.

  10. Reactions of Oxygen and Oxides • Oxygen is extremely reactive. • O2 reacts with most metals to produce normal oxides in which the oxidation number of each oxygen is –2. • The alkali metals are very reactive. • O2 reacts with Li and most of the IIA alkaline earth metals to produce normal oxides.

  11. Reactions of Oxygen and Oxides Oxygen reacts with sodium and barium to produce a peroxide, O2–2 in which the oxidation number of each oxygen is –1 • K, Rb, and Cs are extremely reactive. These react with O2 to produce superoxides in which the oxidation number of each oxygen is –½. High O2 pressure with the other alkaline earth metals can produce peroxides.

  12. Reactions of Oxygen and Oxides Variable oxidation state metals can form variable oxides with oxygen. The oxidation state of oxygen in these is always –2. Reaction with limited oxygen • Reaction with excess oxygen

  13. Reactions of Oxygen and Oxides • Oxygen reacts with nonmetals to form covalent nonmetal oxides. • The oxidation state of oxygen in all of these is –2. • The nonmetal may exhibit many oxidation states. • The Group IVA Elements Reaction with limited oxygen Reaction with excess oxygen

  14. Reactions of Oxygen and Oxides • Group V Elements • Reaction with limited oxygen Reaction with excess oxygen Group VI Elements Reaction with limited oxygen Reaction with excess oxygen

  15. Reactions of Oxygen and Oxides • Nonmetal oxides are acidic anhydrides. • All react with water to produce ternary acids.

  16. Reactions of Oxygen and Oxides • Metal oxides are basic anhydrides. • These react with water to produce ionic metal hydroxides (bases). Metal oxides are usually ionic and basic. Nonmetal oxides are usually covalent and acidic. Metalloid, post transition metals, and some transition metal oxides are amphoteric.

  17. Reactions of Oxygen and Oxides • Nonmetal oxides react with metal oxides to produce salts. (Just like acids and bases.)

  18. Combustion Reactions • All combustion reactions are redox reactions that are extremely exothermic. • Combustion of hydrocarbons

  19. Hydrogen Peroxide • 3% solution sold commercially • 30% soln. used industrially • 70% (explosive) – used for research • 90% – used for research applications Used as an oxidizing agent Used as reducing agent

  20. Ozone • Ozone is one of two allotropes of oxygen (oxygen or dioxygen, O2 being the most common and stable allotrope). Ozone is a powerful oxidizing agent

  21. Water Purification

  22. Water Treatment Preliminary - Rough filtration Primary Treatment Secondary Treatment Bacterial action Tertiary Treatment Removal of nitrates and phosphates

  23. Reactions of Water • Oxidizing agent Reducing agent Disproportionation

  24. Hydrates • MgSO47H2O • BaCl22H2O • CuSO4 7H2O • AlCl3 6H2O • Mg(ClO4)2 6H2O • Hydroscopic – absorbs water spontaneously • Deliquescent – spontaneously absorbs so much water it dissolves • Humectant – moisturizers (food and cosmetics)

  25. End of Chapter 18 and Course

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