John E. McMurry Robert C. Fay Lecture Notes Alan D. Earhart Southeast Community College Lincoln, NE General Chemistry: Atoms First Chapter 18 Hydrogen, Oxygen, and Water Copyright © 2010 Pearson Prentice Hall, Inc.

Chapter 18/2 Hydrogen H 2 (g) + Zn 2+ (aq)2H 1+ (aq) + Zn(s) The French chemist Lavoisier called the gas “hydrogen,” meaning “water former,” because it combines with oxygen to form produce water. Henry Cavendish (1731–1810) in 1766 is credited with isolating hydrogen in its pure form:

Chapter 18/3 Isotopes of Hydrogen Three isotopes: 1.Hydrogen-1 (protium): % abundance 2.Hydrogen-2 (deuterium): 0.015% abundance 3.Hydrogen-3 (tritium): about % abundance H 2 1 H 3 1 H 1 1

Isotopes of Hydrogen

Chapter 18/5 Isotopes of Hydrogen Isotope Effects K w = x D 3 O 1+ (aq) + OD 1- (aq)2D 2 O(l) K w = 1.01 x H 3 O 1+ (aq) + OH 1- (aq)2H 2 O(l) 2D 2 O(l)2D 2 (g) + O 2 (g) Electrolysis 2H 2 O(l)2H 2 (g) + O 2 (g) Electrolysis Slower Faster

Preparation and Uses of Hydrogen 2H 2 (g) + O 2 (g)2H 2 O(l)∆H° = +572 kJ

Chapter 18/7 Preparation and Uses of Hydrogen All large-scale, industrial methods for producing hydrogen use an inexpensive reducing agent such as hot iron, carbon, or methane (natural gas): ∆H° = +131 kJ Fe 3 O 4 (s) + 4H 2 (g)4H 2 O(g) + 3Fe(s) Heat ∆H° = -151 kJ CO(g) + H 2 (g)H 2 O(g) + C(s) 1000 °C

Chapter 18/8 Preparation and Uses of Hydrogen Currently, the most important industrial method for producing hydrogen is the three-step, steam-hydrocarbon re-forming process. ∆H° = -41 kJ CO 2 (g) + H 2 (g)CO(g) + H 2 O(g) Catalyst 400 °C 3.Third Step: Removal of excess carbon dioxide: 1.First Step: The production of synthesis gas: ∆H° = +206 kJ CO(g) + 3H 2 (g)H 2 O(g) + CH 4 (g) Ni catalyst 1100 °C 2.Second Step: The water-gas shift reaction: CO 3 2- (aq) + H 2 O(l)CO 2 (g) + 2OH 1- (aq)

Chapter 18/9 Preparation and Uses of Hydrogen Methanol synthesis: Haber process: CH 3 OH(l)CO(g) + 2H 2 (g) Catalyst Cobalt 2NH 3 (g)N 2 (g) + 3H 2 (g)

Chapter 18/10 Reactivity of Hydrogen H 1- (g)H(g) + e - E ea = -73 kJ/mol H 1+ (g) + e - H(g) E i = kJ/mol While hydrogen gas is relatively unreactive at room temperature, gas mixtures with as little as 4% hydrogen by volume in air are highly exothermic and potentially explosive: Alkali-metal-like reaction to form hydrogen ion: ∆H° = -572 kJ2H 2 O(l)2H 2 (g) + O 2 (g) Halogen-like reaction to form hydride ion:

Binary Hydrides

Chapter 18/12 Binary Hydrides Ionic Hydrides The hydride ion is a good proton acceptor (Brønsted-Lowry base): ∆H° = kJ CaH 2 (s)Ca(s) + H 2 (g) 400 °C ∆H° = kJ 2NaH(s)2Na(l) + H 2 (g) 400 °C Saltlike, high melting, white, crystalline compounds formed by the alkali metals and the heavier alkaline earth metals Ca, Sr, and Ba: 2H 2 (g) + Ca 2+ (aq) + 2OH 1- (aq)CaH 2 (s) + 2H 2 O(l)

Chapter 18/14 Binary Hydrides Covalent Hydrides Common hydrides of nonmetallic elements, such as diborane (B 2 H 6 ), methane (CH 4 ), ammonia (NH 3 ), water (H 2 O), and hydrogen halides (HX; X = F, Cl, Br, or I ). In general, their intermolecular forces are relatively weak so they exist as gases or volatile liquids at ordinary temperatures.

Chapter 18/15 Binary Hydrides Metallic Hydrides Formed by the reaction of the lanthanides and actinide metals and certain d-block transition metals with variable amounts of hydrogen with the general formula MH x. PdH x (s)Pd(s) + H 2 (g) 2 x Favored at lower temperature Favored at higher temperature

Chapter 18/16 Oxygen Priestly called the gas “dephlogistated air.” Lavoisier called it “oxygen” which means “acid former.” Gaseous O 2 condenses at -183 °C to form a pale blue liquid and freezes at -219 to give a pale blue solid. Joseph Priestly and Karl Wilhelm Scheele are credited for isolating and characterizing oxygen between 1771 and 1774: 2Hg(l) + O 2 (g)2HgO(s) Heat

Chapter 18/18 Preparation and Uses of Oxygen 2H 2 O 2 (aq)2H 2 O(l) + O 2 (g) Catalyst Small amounts of oxygen can be generated in the lab: 2H 2 O(l)2H 2 (g) + O 2 (g) Electrolysis 2KCl(s) + 3O 2 (g)2KClO 3 (s) MnO 2 catalyst Heat Photosynthesis constantly replaces used oxygen: 6O 2 + C 6 H 12 O 6 6CO 2 + 6H 2 O h Glucose

Chapter 18/19 Reactivity of Oxygen 2MgO(s)2Mg(s) + O 2 (g) 2Li 2 O(s)4Li(s) + O 2 (g) Oxygen will react with active metals, such as lithium and magnesium, to give ionic oxides:

Reactivity of Oxygen 2H 2 O(l)2H 2 (g) + O 2 (g) P 4 O 10 (s)P 4 (s) + 5O 2 (g) CO 2 (g)C(s) + O 2 (g) 8SO 2 (g)S 8 (s) + 8O 2 (g) With nonmetals such as hydrogen, carbon, sulfur, and phosphorus, oxygen forms covalent oxides:

Reactivity of Oxygen In covalent compounds, oxygen often forms a double bond with carbon and oxygen. However, with larger atoms double bond formation is less common.

Chapter 18/22 Reactivity of Oxygen

Chapter 18/23 Oxides

Chapter 18/24 Oxides Basic Oxides Also called basic anhydrides. These compounds are ionic and formed by metals on the left side of the periodic table. Mg 2+ (aq) + H 2 O(l)MgO(s) + 2H 1+ (aq) Water-insoluble basic oxides dissolve in strong acids: 2Na 1+ (aq) + 2OH 1- (aq)Na 2 O(s) + H 2 O(l) Water-soluble basic oxides dissolve in water:

Chapter 18/25 Oxides Acidic Oxides Also called acid anhydrides. These compounds are covalent and formed by nonmetals on the right side of the periodic table. SiO 3 2+ (aq) + H 2 O(l)SiO 2 (s) + 2OH 1- (aq) Water-insoluble basic oxides dissolve in strong bases: 2H 1+ (aq) + 2NO 3 1- (aq)N 2 O 5 (s) + H 2 O(l) Water-soluble acidic oxides dissolve in water:

Chapter 18/26 Oxides Amphoteric Oxides These compounds exhibit both acidic and basic properties. 2Al(OH) 4 1- (aq)Al 2 O 3 (s) + 2OH 1- (aq) + 3H 2 O(l) 2Al 3+ (aq) + 3H 2 O(l)Al 2 O 3 (s) + 6H 1+ (aq) For example, Al 2 O 3 is insoluble in water, but it dissolves both in strong acids and strong bases:

Oxides

Peroxides and Superoxides When some of the group 1A and group 2A metals are heated in excess oxygen, they will form either peroxides, such as Na 2 O 2 and BaO 2, or superoxides, such as KO 2, RbO 2, and CsO 2.

Chapter 18/29 Peroxides and Superoxides O 2 (g) + 2K 1+ (aq) + HO 2 1- (s) +OH 1- (aq)KO 2 (s) + H 2 O(l) Superoxides can dissolve in water: 2Na 1+ (aq) + HO 2 1- (aq) + OH 1- (aq)Na 2 O 2 (s) + H 2 O(l) The peroxide ion is a basic anion: BaSO 4 (s) + H 2 O 2 (aq)BaO 2 (s) + H 2 SO 4 (aq) Peroxides will react with strong acids:

Chapter 18/30

Chapter 18/31 Hydrogen Peroxide Pure hydrogen peroxide freezes at -0.4 °C and is estimated to boil at 150 °C.

Chapter 18/32 Hydrogen Peroxide O 2 (g) + 2H 1+ (aq) + 2e - H 2 O 2 (aq) 5O 2 (g) + 2Mn 2+ (aq) + 8H 2 O(l) 5H 2 O 2 (aq) + 2MnO 4 1- (aq) + 6H 1+ (aq) E° = V E° = 1.78 V As a reducing agent: Hydrogen peroxide is both a strong reducing agent and a strong oxidizing agent: 2H 2 O(l)H 2 O 2 (aq) + 2H 1+ (aq) + 2e - 2H 2 O(l) + Br 2 (aq)H 2 O 2 (aq) + 2H 1+ (aq) + 2Br 1- (aq) As an oxidizing agent:

Chapter 18/33 Hydrogen Peroxide

Chapter 18/35 Ozone 2O 3 (g)3O 2 (g) discharge Electric ∆H° = +285 kJ Oxygen exists in two allotropes: ordinary oxygen (O 2 ) and ozone (O 3 ). Ozone is a toxic, pale blue gas and is produced when an electric discharge passes through O 2 :

Chapter 18/36

Chapter 18/37 Ozone While dilute gaseous ozone decomposes slowly, the concentrated gas, liquid ozone (bp -111 °C), and solid ozone (mp -193 °C) can all decompose explosively. Two resonance structures are needed to explain the structure of the ozone molecule because the two O-O bonds have equal lengths:

Chapter 18/38 Ozone A standard method for detecting ozone in polluted air is to pass the air through a basic solution of potassium iodide that contains a starch indicator: O 2 (g) + I 2 (aq) + 2OH 1- (aq)O 3 (g) + 2 I 1- (aq) + H 2 O(l) E° = 2.08 V Ozone is an extremely powerful oxidizing agent: O 2 (g) + H 2 O(l)O 3 (g) + 2H 1+ (aq) + 2e - Starch and iodine combine to form a deep blue complex.

Chapter 18/40 Water It’s estimated that there is approximately 1.35 x m 3 of water in the oceans, which accounts for 97.3% of the Earth’s total water supply. Freshwater lakes and rivers account for less than 0.01% of the total (about 1.26 x m 3 ).

Chapter 18/41 Water

Chapter 18/42 Water Water that contains appreciable concentrations of doubly charged ions such as Ca 2+, Mg 2+, and Fe 2+ is called hard water. CO 2 (g) + H 2 O(l) + CO 3 2- (aq)2HCO 3 1- (aq) Heat Boiler scale is made of metal carbonate precipitates. CaCO 3 (s)Ca 2+ (aq) + CO 3 2- (aq)

Chapter 18/43 Water (RSO 3 1- ) 2 Ca 2+ (s) + 2Na 1+ (aq)2RSO 3 1- Na 1+ (s) + Ca 2+ (aq) Ion exchange is a process that replaces Ca 2+ and Mg 2+ with Na 1+ : Resin (R) with SO 3 2- and Na 1+ attached Soft waterHard water

Chapter 18/44 Reactivity of Water Cl 2, Br 2, and I 2 disproportionate in water: H 2 (g) + 2Na 1+ (aq) + 2OH 1- (aq)2Na(s) + 2H 2 O(l) Water is reduced by alkali and the heavier alkaline earth metals: H 2 (g) + Ca 2+ (aq) + 2OH 1- (aq)Ca(s) + 2H 2 O(l) Fluorine is the only element able to oxidize water: O 2 (g) + 4HF(aq)2F 2 (g) + 2H 2 O(l) HOCl(aq) + H 1+ (aq) + Cl 1- (aq)Cl 2 (g) + H 2 O(l)

Chapter 18/45 Hydrates Compounds that absorb water from the air are hygroscopic and can be used as drying agents. CuSO 4 5H 2 O Hydrates: Solid compounds that contain water molecules. Mg(ClO 4 ) 2 6H 2 O AlCl 3 6H 2 O CoCl 2 6H 2 O(s)CoCl 2 (s) + 6H 2 O(l)