directly from solid to gas!

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1 430 Largest use of CO 2 (~50%) is not a chemical use but a refrigerant CO 2 (s) dry ice CO 2(s) f.p. = C.5 > C 78 CO 2(g) sublimation directly from solid to gas! How do you get liquid CO 2? You have to keep a pressure on the solid when it is melting. CO 2 is a liquid CO 2(l) at 5.2 atm and -5.6 C CO 2(l) is used to extract caffeine from coffee. It leaves no harmful residues. CO 2(l) is used in fire extinguishers. The more dense CO 2 will displace air around the burning material and keep O 2 from fueling the flames. ~25% of CO 2 produced is used in carbonation of beverages Chemistry of Soda CO 2(aq) + H 2 O H 2 CO 3(aq) - H 2 CO 3(aq) + H 2 O HCO 3 (aq) + H 3 O +

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3 CO 2 Reaction with Base: CO 2(aq) + OH - - (aq) HCO 3 (aq) - HCO 3 (aq) + OH - 2- (aq) CO 3 (aq) + H 2 O (l) Other carbon compounds Cyanides CN - [:C N:] -1 strong base NaCN sodium cyanide HCN hydrogen cyanide (weak acid) Reaction of CN - with water: CN - (aq) + H 2 O HCN (aq) + OH - (aq) equilibrium Reaction of CN - with a strong acid: strong base CN - (aq) + HCl (aq) HCN (aq) +Cl - (aq) strong acid Reaction is complete! Properties of Cyanides HCN is extremely poisonous - it was used in gas chambers. CN - binds to the heme in your mitochondria that transport O 2. Not the same heme as CO which is your blood heme. NaCN is also lethal Hemoglobin in blood is based on Fe Heme in mitrochondria is Cu based 432

4 433 Nitrogen 78% of air is N million tons N 2 / year Industrial Preparation of N 2 : Air liquify N 2 (collected first) Ar O 2 Uses of N 2 : Enhanced oil recovery to force oil from subterranean deposits (~30% of N 2 made) Coolant (low b.p. 77k (-196 C)) freezing perishables (meat, seafood) Unreactive gas in chemical industry used as a blanketing atmosphere Nitrogen Cycle helps to maintain balance of N 2 in the atmosphere. Plants remove N 2 to make NH 3 Plants decay back to N 2

5 434 Nitrogen Fixation: Name given to the reactions that microorganisms use to make NH 3 from N 2. Ammonia: Sharp odor Irritates lungs. Can cause death if inhaled in large quantities Used as a fertilizer by injecting directly into the soil Haber Bosch Process: catalysts N 2 (g) + 3H 2 (g) 2NH 3 (g) H = KJ atm requires a catalyst and high pressure H = KJ is the heat of reaction C Negative H means exothermic. The extreme conditions are required because of the large kinetic barrier to the reaction. kinetic barrier N 2 + H 2 energy released NH 3

6 Properties of NH 3 : b.p C f.p C very soluble in H 2 O due to H-bonding ability. It is a weak base in H 2 O NH 3(aq) + H 2 O NH 4 (aq) + OH - (aq) (an equilibrium exists in H 2 O) Reacts completely with strong acids NH 3(aq) + HCl (aq) NH 4 Cl (aq) Dissolves Group IA, IIA metals Na + NH 3(l) Na + + NH 3(l) + e - The e - is solvated by NH 3!! Amides NH 2 - NH 2 - is a powerful base and is found in combination with metals such as Na + and K - Amides react with H 2 O to give strongly basic solutions. NaNH 2 + H 2 O NH 3(aq) + NaOH (aq) (very exothermic reactions!)

7 Ammonium NH NH 4 + is slightly acidic Reacts with bases: NH 4 + Cl - (aq) + NaOH (aq) NH 3(aq) + NaCl (aq) + H 2 O (l) Nitrides N 3- N 3- combined with metals (i.e. Mg 3 N 2, Li 3 N) are ionic N 3- combined with non-metals (i.e. P 3 N 5, BN) are covalent Nitric Acid HNO 3 The most important oxo acid of nitrogen Resonance forms of Lewis structure

8 437 Ostwald Process to make Nitric Acid: Very important reaction Discovered by the German scientist Ostwald in 1902 It s discovery is thought to have prolonged WWI because Germany had been cut off from importing nitrate salts from Chile by the Allies. Nitrates are used in explosives. Oswald Process is 3 steps: Pt/Rh ºC (1) 4NH 3(g) + 5O 2(g) 4NO (g) + 6H 2 O (g) (Ammonia to nitric oxide) H = KJ Very exothermic! (2) 2NO (g) + O 2(g) 2NO 2(g) This is down-stream from the NH 3 + O 2 reaction (1). (nitric oxide to nitrogen dioxide) (3) 3NO (g) + H 2 O 2HNO 3(aq) + NO (g) (nitrogen dioxide to nitric acid and nitric oxide)

9 Overall: NH 3(g) + 2O 2(g) HNO 3(aq) + H 2 O Uses of Nitric Acid HNO 3 1) To make NH 4 NO 3 for fertilizers NH 3 + HNO 3 NH 4 NO 3 2) To make NH 4 NO 3 for explosives Alfred Nobel, a Swedish chemist, discovered how to safely handle nitroglycerine with the NH 4 NO 3 and amassed a fortune, some of which he used to fund the Nobel Prizes. 438 NH 4 NO 3 is unstable. Decomposition of NH 4 NO 3 : Under mild conditions: NH 4 NO 3 (s) ºC N 2 O(s) + 2H 2 O(g) With strong heating: 2NH 4 NO 3 (s) >300 ºC 2N 2 (g) + O 2 (g) + 4H 2 O(g) (2 moles solid = 7 moles of gas) Rapid expansion occurs! The violent explosion of a ship being loaded with fertilizer (NH 4 NO 3 ) in Texas City, Texas took the lives of ~600 persons in 1947.

10 439 Other Nitrogen Explosives Nitroglycerine C 3 H 5 N 3 O 9 (liquid) 4C 3 H 5 N 3 O 9 6N CO + 10H 2 O + 7O 2 Nitroglycerine (4 molecules of liquid 35 moles of gas!) The expanding gases cause a violent detonation but no smoke! Dynamite this is a mixture of Nitroglycerine/NH 4 NO 3 /wood pulp/caco 3 (this is a filter used to neutralize any acids that may form during storage) TNT trinitrotoluene (solid) C 7 H 5 N 3 O 6 (s) huge 3N 2 + 7CO 2 + 5H 2 O + 7C (s) entropy (15 moles of gas) increase

11 440 Oxygen 50% of all atoms on earth are oxygen. 61% of all atoms in earth s crust are O. (crust is km thick) O 2 Diatomic Colorless, odorless, tasteless Allotropes: (different molecular forms of the same element) O 2 O 3 Isotopes: Three for O: 16 O 17 O 99.8% 0.2% 18 O } Dry air is ~ 21% of O 2 this has not changed for millions of years due to the oxygen cycle in nature which maintains the balance.

12 Oxygen consumed oxygen produced - respiration - photosynthesis by cholorophyll- - decay containing organisms - combustion of fuels 441 Photosynthesis nco 2 + nh 2 O (CH 2 O) n + no 2 carbohydrates (especially glucose) Note: >50% of all O 2 from photosynthesis comes from photoplankton in oceans The cycle continues when decay, respiration and combustion take O 2 back to CO 2 and H 2 O. Q What would happen if the oxygen cycle did not maintain O 2 concentration in air at ~21%? A Everything would burn out of control - forest fires, house fires etc., Why? sunlight

13 Because the rates of reactions increase with higher concentrations of reagents. 442 Industrial Production of O 2 : Air liquify Liquid Air N 2 (1) Ar (2) O 2 (3) N 2, Ar boil off first; wait to collect pure O 2 Laboratory (small scale) Synthesis of O 2 : MnO 2 (cat) ºC 2 KClO 3(s) 3O 2(g) + 2KCl (s) Uses of O 2 : (top 5 th chemical in the U.S. ~ 19 million tons) 1) steel industry blast furnaces 2) chemical industry plastics 3) sewage treatment aerobic bacteria 4) health industry respirators 5) rocket industry fuel

14 Pungent odor Lewis structure/vsepr Ozone O Importance of O 3 for life: It absorbs hυ in the UV range which screens us from this harmful radiation O 3 + UV light O 2 + O Oxidizing Ability of O 3 Very strong oxidant in basic and acidic media. Second only to fluorine in its oxidizing ability Ozone is a dangerous pollutant in smog. It attacks trees, fabrics, rubber, plastics, & lungs! - at % O 3 in air (0.5 parts per million) young children and elderly people are at risk - at % O 3 (1 ppm) O 3 is dangerous to everyone

15 Oxides 444 All elements except Noble gases form oxides Three catagories: (THIS IS ALL REVIEW) Basic ionic oxides (form with metals) Acidic covalent oxides (form with non-metals, metalloids, some metals) Amphoteric can be ionic or covalent (form with metals) Basic Oxides Form OH - in H 2 O Groups I, IA (except Be), In, Tl, some transition metals Examples: NaO (s) + H 2 O 2NaOH (aq) δ + δ + - δ MgO (s) + H 2 O Mg(OH) 2(s) (insoluble hydroxide)

16 Acidic Oxides Form acids in water All non-metals except noble gases. SO 3, SO 2, NO, NO 2, SiO 2, Sb 2 O 3, etc., and some transition elements 445 Examples: SO 3 + H 2 O H 2 SO 4(aq) CrO 3 + H 2 O H 2 CrO 4(aq) Amphoteric Oxides Can be either acidic or basic Al, Ga, Sn, Pb and most transition metals They can neutralize acid or base Example: Al 2 O 3 (amphoteric) (C) Al 2 O 3(s) + 2OH - (aq) + 7H 2 O 2[Al(H 2 O) 2 (OH) 4 ] - (aq) (B) Al 2 O 3(s) + 6H + (aq) + 9H 2 O 2[Al(H 2 O) 6 ] 3+ (aq) In reaction (A), Al 2 O 3 is an acid In reaction (B), Al 2 O 3 is a base

17 How do you predict if a transition metal oxide will be acidic, basic or amphoteric? 446 Two trends Trend 1 The higher the oxidation state of the metal, the more covalent (acidic) it will be. Trend 2 The lower the oxidation state of the metal, the more ionic (basic) it will be. Consider: Cr +2 O, Cr 2 +3 O 3, Cr +6 O 3 Most ionic is CrO (lowest ox. state) Most covalent is CrO 3 (highest ox. state) CrO would be basic CrO 3 would be acidic Cr 2 O 3 would be amphoteric Practice these: Mn 2 O 3, MnO, [MnO 4 ] - OsO 4, OsO 2, OsO

18 447 Peroxides (O 2 2- ) ox. state is O -1 Hydrogen peroxide: H 2 O 2 - colorless liquid - strong oxidizing agent - used as a bleach, disinfectant Δ H 2 O 2 H 2 O + ½O 2 Exothermic! Alkali Metal Peroxides: M 2 O 2 Na 2 O 2 K 2 O 2 M + - O-O - M +

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