Popular in Course
Popular in Chemistry
This 12 page Class Notes was uploaded by Carmela Kilback on Wednesday September 9, 2015. The Class Notes belongs to CHEM 165 at University of Washington taught by Staff in Fall. Since its upload, it has received 57 views. For similar materials see /class/192603/chem-165-university-of-washington in Chemistry at University of Washington.
Reviews for H
Report this Material
What is Karma?
Karma is the currency of StudySoup.
Date Created: 09/09/15
Chemistry 165 2171 Chapter 21 Sulfur Nitrogen and Phosphorus OXtoby pages 7547776 Sulfur Volcanic deposits aka quotbrimstonequot were sources in antiquity The first major application was gunpowder which is made from saltpeter NaNOg powdered charcoal and sulfur in m 751510 proportions The elemental nature of sulfur was established in 1809 by Guy Lussac Sulfur is quite abundant 340 ppm 16th and is ubiquitous in nature in both organic and inorganic forms eg cysteine and methionine are essential amino acids Modern sources of S are the Frasch process HZS in quotsourquot natural gas metal sulfide ores The Frasch process uses superheated steam to melt sulfur mp 119 C and bring it to the surface The HZS in natural gas is recovered with base HZS gt SH Ht similar to H20 The Claus process is used to convert HZS to S HZS g Jr 02 g gt S02 53 H20 53 1 HzS g02g gtSgHZO g 2 2st gSOzg egt 35g2H20 g 3 300 C Reactions 1 and Z are quotcombustionquot reactions The resulting S02 is then reacted with additional HzS over an oxide catalyst to give sulfur Multiple reactors and stringent air pollution legislation together achieve gt99 conversion A similar sequence is used for S production from crude oil except that organosulfur compounds are first converted to HzS by a hydrogenation process The large amounts of S02 generated in the roasting of sulfide ores are not converted to S but are used directly in the production of sulfuric acid see below Structure of Sulfur In contrast to OZ sulfur is not a gas because of the larger atomic radius and consequently weaker 139 bonds Sulfur forms eightemembered rings in all the stable allotropes Chemistry 165 2172 Sulfuric Acid Very early alchemists FeSO4 7 H20 5 H2804 l FeO s 6 H2O g Lead chamber process 1746 s s L set is soa is mostly some this is the desirable product 503 g H20 1 gt H2804 1 Presence of KN03 N02 source was found to help 502 gN02 g gt503 gN0g But this is stoichiometric in N02 expensivel Guy Lussac developed a way to refuse the 2 NO g T 02 g H20 1 gt 2 HN02 aq nitrous acid 2 HNO2 aq 802 g gt H2SO4 aq 2 NO g overall reaction 0ng i02g gt503g Current process called contact process Recall the thermodynamics of the above reaction S02 5 1 02 g gt 803 g AHquot 7989 k ASquot 7940 JK1 at AG 0 T 1050K worse at higher T High T is not helpful Practical processes use metal oxide catalysts at 4007600 C Multiple pass reactors give efficient conversion The last 05 of SO 2 can be converted using an electrochemical oxidation to produce H28203 anode 2 H2804 aq 2 H20 1 gt H28203 aq Z H30 2 e cathode Z H30 aq 2 e gt H2 g 2 H20 1 then H25203 aq H20 1 gt H2505 H2504 peroxydisulfuric acid peroxymonosulfuric acid H2505 aq 502 g H20 1 gt 2 H2504 aq Chemistry 165 2173 Legislation requires low 802 emissions H2804 production contributes only about 2 of total 802 emissions to the atmosphere Uses of Sulfuric Acid Note that this is a very cheap chemical The cost is approximately 100 ton ca 10 kilo Fertilizer 65 Chemical manufacture 5 Petroleum refining 5 Metallurgical 5 Related chemistry Sulfite paper process 5025 H20 1 gt stogaq 1 HSO aq sulfurous acid Mildly acidic medium Add base usually from Mg0 to moderate pH After digestion pulp is filtered off and the solution evaporated Organic residues are burned for process heat MgHSOS2 S gt Mg0 8 H20 9 Z 502 g Sulfate process employs a very basic medium of Na2S and NaOH After hours at 175 C l pulp is filtered off Oxidation of 82 and HS to 8042 has also occurred Some additional Na2804 is added to make up for losses The solution is then concentrated to dryness and burned to generate process heat during which organic matter reduces the 8042 to 82 Na2804 2 quotCquot gt Na2S s 2 C02 g The C02 reacts with NaOH 2 Na0H s C02 g gt Na2C03 s H20 g Lime is generated separately CaC03 s A Ca0 s C02 g Ca0 s H20 1 gt Ca0H2 aq The Ca0H2 is added to the Na2C03 solution Na2C03 aq Ca0H2 aq gt CaC0T3 s Z Na01H recycle to recycle to lime kiln pulp reactor Chemistry 165 2174 Need some sodium sulfate 4 NaCl aq 2 802 g 2 H20 1 02 g gt NazSO4 4 HCl Preparation of Thiosulfate SgOgZ N OH HSO3 aq L NaSOSZ39 S 1A 2 thiosulfate S 20 3 reducing agent S4062 2 e Selenium Tellurium Polonium Po discovered by M Curie in 1898 from uranium residues Her second Nobel prize in 1 9 1 1 Se and Te From anode slimes of Cu process Chemistry 165 21 5 Phosphorus Isolated from urine by Brandt in 1669 First detected in plants by Albino in 1688 In 1769 P was found to be a plentiful constituent of bones of animals bone meal fertilizer quotSuperphosphatequot fertilizer was patented in 1843 General Comparison of Phosphorus and Nitrogen N2 is a gas P is a solid Basic structural unit is P4 tetrahedron white P For N o and 27 bonds for P 36 is more stable Atomic radius of P is 11 A N is 075 A a b C white P black P red P P is less electronegative than N but will form phosphides with highly electropositive elements such as Ca eg Ca3P2 In phosphides the formal oxidation state of P is 3 Ca3P2 S 6 H20 1 gt 2 PH3 g 3 CaOH2 PII3 has bp 88 C compare NH339s bp of 33 C i343 versus 3151 similar situation but P is less electronegative Since P has less negative charge in PH3 vs N in NH3 PH3 is less basic than NH3 Supplies of PH3 also often have small amounts of P2II4 diphosphine This material is spontaneously ammable in air Once started PII3 burns quite well PH3 g 2 02 g gt H3PO4 S AH f 54 0 1279 Sources ofP P is found in phosphate rock which is largely Ca5PO43F uoropatite This works as a fertilizer but a more soluble form can be generated by treatment with II2SO4 2 Ca5PO43F S 7 H2804 l 17 H2O l gt 3 CaII2PO42II2O S 7 CaSO42 H2O S 2 HF g The wet acid process gives phosphoric acid directly Ca5PO43F aq 5 II2SO4 aq 10H2O l gt 3 H3PO4 aq 5 CaSO42 H20 5 HF g HF is trapped by reaction with SiF4 to give II2SiF6 which is used to uoridate water The gypsum CaSO4 is filtered off and sold for wallboard The H3PO4 solution is concentrated by evaporation Chemistry 165 2176 Pure H3PO4 can be made by the electric arc furnace process 2000 C 12 Ca5PO43F 0 43 SiOz 0 90 C s gt 90 CO g 20 3 CaOSiOz 0 3 SiF4 g 9 P4 g The P is burned in air P4 5 5 02 g gt P4010 S P4010 s 6 H20 gt 4 H3PO4 aq Chemistry 165 Structures of some P oxides P4 3 02 gt P406 One oxygen caps each of the edges of the P4 tetrahedron P4 5 02 gt P4010 As above plus one terminal 0 on each P Oxyacids of P some of many phosphoric H3PO4 phosphorous or H3P03 phosphonic hypophosphorous or H3POZ phosphinic 5 3 1 Ar Chemistry 165 2178 Nitrogen N forms the very stable diatomic molecule N2 bond enthalpy 945 k No other stable allotropes are known lonic nitride forms with Li 3 Li 5 T1 N2 g gt Li3N s Li3N s 3 H20 1 gt NH3 g 3 LiOH aq Much of the nitrogen on the surface of the planet is present as N2 This unreactive form is not readily used by living organisms Some bacteria have enzymes called quotnitrogenasesquot which allow N2 to be quotfixedquot into usable forms Certain plants legumes harbor these bacteria in root nodules Other plants require additional nitrogen fertilizer for optimum growth Ammonia is the key starting material for nitrogen chemistry Ammonia Synthesis Electric arc process basically simulates lightning strikes to make oxides of N Not practical Cyanamide process CaO s 3 C s A CaC2 s CO CaC2 s N2 g A CaCN2 s CaCN2 s H20 1 gt CaOH2 CO2 g Z NH3 g Energy requirements are prohibitive Cyanamide is still used in the manufacture of plastics Haber process Direct reaction of N2 with H2 N2 g 3 H2 g lt gt Z NH3 g AHquot 7922 AGquot 733 as written Compare to acetylene HCCH g3H2 glt gtZCH4g AG 7311 Low driving force for ammonia synthesis is attributable to the very strong NN bond Chemistry 165 2179 For NH3 formation K 413 e WRT but the reaction is very slow at 298 K 6x1205at238K Perhaps raise T to 800 K to improve rate What will be K at 800 K Use van39t Hoff equation 1nm Li L1 R K800 298 K298 4 gtlt1075 In practice run the reaction at high P 200 atm and fairly high T with a catalyst Fe203 A1203 Relatively low yields 15 are obtained but the product NH3 is easily separated and the N2 and H2 are recycled Chemistry of NHg The boiling point of NH3 is 733 C as opposed to PH3 whose boiling point is 788 C NH3 has many similarities to H2O It is a good solvent for ions but also dissolves nonepolar organic species quite well NH3 is basic NH3 aq H20 1 gt NH4 aq OH aq NH3 is acidic Z NH3 1 2 Na 5 gt NaNH2 s H2 g Note that the above reaction only occurs at a reasonable rate in the presence of a transition metal catalyst Without a catalyst Na dissolves in NH3 to give Nat 501 and e 501 where quotsolquot means solvated by ammonia NH3 reacts with excess halogen C12 F2 Br2 or 12 to give NF3 NC13 NBrg and N13 respece tively These trihalides are increasingly unstable with the heavier halogens N13 blows up Hydrazine Z NH3 aq OCl aq gt NH27NH2 aq Cl aq H20 1 This is the Raschig process It actually occurs in two steps via NH2Cl NH3 aq OCl aq gt NH2C1 aq OH aq NH3 aq NH2C1 aq gt NH27NH3 aq Cl aq NH27NH3 aq OH aq gt NH27NH2 aq H20 1 Oxoacids of S P and N The ability of oxoacid solutions to act as oxidizing or reducing agents depends upon the pH of the solution When reduction of an oxoanion requires removal of oxygen the reaction comsumes H For example nitric acid is a stronger oxidizing agent at pH 0 than at pH 14 Chemistry 165 21710 pH0 NOg 3H30 Ze gt HNOZ 4H20 8 99V pH 14 N03 H20 Ze gt N02 ZOH 8 01V Sulfuric acid is a mild oxidizing agent pH 0 HSO4 3HgoJr Ze gt 02 5H20 8 17V But under basic conditions a sulfur oxoanion such as sulfite 8032 sulfur is in oxidation state 4 are good reducing agents 0424 HZO Ze gt 8032 ZOH 8 lt98V Oxidation State and Acid Strength see table 211 We know that nitric acid HNOg is a strong acid and phosphoric acid H3PO4 is a weaker acid We will learn in Chapter 22 that perchloric acid HClO4 Cl is in the 7 oxidation state is a y strong acid We might suspect the high acidity has something to do with high oxidation state If we instead focus on the stability of the conjugate base we find that the greater the number of lone oxygen atoms on the central atom the more the negative charge can be delocalized By writing the oxoacids as XOnOHm we find that acidity increases dramatically as n increases ie PO OH3 weak n1 NOZOH strong nZ ClO3OH V strong n3 Chemistry 165 21711 Explosives Explosives are materials that decompose rapidly and exothermically to produce a large volume of gas Useful safe explosives need to be thermodynamically unstable but kinetically stable to allow long term storage prior to controlled detonation Name Formula Products Exp gigfl kJ g l Gunpowder I Z KNOB 3C S I N2 SCOZ KZS I 721 Nitrocellulose I C24H29 OgNOg11 I 205CO 35 C02 145HZO 55N2 I 745 Nitroglycerin I C3H5N033 I SCOZ 25HZO 15NZ 02502 I 764 Ammonium nitrate I NH4NOg I ZHZO N2 0502 I 716 TNT I C6H2CH3NOZ3 I 35CO 35C 25HZO 15 N2 I 74 4 Picric acid I C6HZOHNOZ3 I 55CO 15HZO 05C 15N2 I 744 Ammoniumpicrate I C6HZNOZSONH4 I 4C0 2C SHZO 2N2 I 726 Tetryl I C7H5N508 I 5500 25H20 15C 25NZ I 4 Mercury fulminate I HgONC2 I Hg ZCO N2 I 715 Lead azide I PbN6 Pb 3N2 I 715 Gunpowder China 1000 AD was the material of choice until the mid719th C when it was supplanted by guncotton prepared by treating cellulose cotton with nitric acid Trinitrotoluene TNT is used widely in the military and in mining applications It is made by nitration of toluene Chemistry 165 21712 Nitroglycerin is made from glycerin a triol and nitric acid sto4 A 3HNO3 gt M 3H20 Ho OH N02 N02 OH No2 Alfred Nobel discovered that a stable storable form of nitroglycerin could be made by absorbing it onto diatomaceous earth high surface area silica This mixture became known as dynamite and made Nobel very wealthy Dynamite has been largely replaced in mining applications by mixtures of ammonium nitrate with fuel oil Decomposition of NH4N03 can be noneeXplosive NH4N03 s gt N2 g ZHZO g loz g AGquot 273k