Chemistry - an illustrated guide to science (794128), страница 14
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Any excess that is applied to soilis readily washed out into streams andrivers, where it causes environmentalproblems.Percentage of nitrogenAmmonium nitrateNH4 NO335.0 0Ammonium sulphate(NH4 ) 2SO421.21UreaH2NCONH246.672NH3(aq) + H2SO4 (aq) ➞(NH4 ) 2SO4 (aq)● Ureais a waste product of animalmetabolism and is excreted from thebody in sweat and urine. It is madeindustrially by the reaction ofammonia with carbon dioxide. Thisreaction is carried out at 200 °C and200 atmospheres:CO2(g) + 2NH3(g) ➞H2NCONH2(l) + H2O(g)© Diagram Visual Information Ltd.RH2 Nnitric acidprotein80PATTERNS—NON-METALSKey wordscatalystdouble bondenzymegroup 6oxygensulfurOxygen and sulfur1 Atoms and moleculesO1 Atoms and moleculesand su lfu r are both in grou p 6of the periodic table.
Atoms of eachelement have six electrons in the outerelectron shell and require twoelectrons to fill the shell.● Oxygen exists as oxygen molecules,O2, in which each oxygen atomprovides two electrons. The oxygenatoms are held together by a dou blebon d, O=O.● At room temperature, sulfur exists as amolecule composed of eight sulfuratoms, S8 , arranged in the shape of acrown.OOxygen atom● OxygenOxygen molecule O2SSSulfur atomSSS3216 SSSSSSulfur molecule S8(crown-shaped)2 Laboratory preparation of oxygen2 Laboratory preparationof oxygenis prepared in the laboratoryby the decomposition of hydrogenperoxide using a suitable catalyst,such as manganese dioxide:168OOabcd● Oxygenaliquid reactant – hydrogensolid catalyst – manganese oxidewateroxygend2H2O2(l) ➞ O2(g) + 2H2O(l)● Hydrogenperoxide is rapidlydecomposed by a variety of catalysts,including the en zym e catalase.
In onesecond, one molecule of catalase candecompose up to 50,000 molecules ofhydrogen peroxide.● Oxygen is only slightly soluble and canbe collected over water.● Hydrogen peroxide is usually suppliedin solutions designated by volumestrength. For example, 20-volumehydrogen peroxide yields 20 volumesof oxygen gas per volume of solution.3 Physical properties ofoxygen and sulfur© Diagram Visual Information Ltd.● Atroom temperature, oxygen is acolorless, odorless gas, while sulfur is ayellow solid.cb3 Physical properties of oxygen and sulfurPhysical propertiesOxygenSulfurm.p./ °C–218119b.p./ °C–183444Density g/ dm 31.312070ColornoneyellowSmellnoneslightSolubility0.0 07g per 10 0 g/ H2Oalmost insoluble81Extraction of sulfur—the Frasch processPATTERNS—NON-METALSKey wordsoresulfidesulfursulfur dioxideThe Frasch processProcessing and usesa● Hotcbde150mfghcompressed air and superheatedsteam are piped underground.
Thisforces water and molten su lfu r to thesurface.● The sulfur obtained is about99.5 percent pure, and may be storedand transported molten or allowed tocool and solidify.● A significant proportion of theelemental sulfur used in industry isobtained as a by-product of otherindustrial processes such as therefining of metal su lfide ores andpetroleum refining.● In petroleum refining, sulfurcompounds like thiols ( R-SH) anddisulphides ( R-S-S-R) are removedfrom some of the petroleum fractionsbecause they would damage thecatalysts used in refining processesand also because of their potential tocause environmental problems.
Forexample, if they were not removedfrom fuels like gasoline, they wouldburn to form su lfu r dioxide. This gasdissolves in water in the atmosphere,forming an acid, and wouldsignificantly increase the acidity of rainwater.● Sulfur compounds are converted tohydrogen sulfide by catalytichydrogenation:R-SH(g) + H2(g) ➞R-H(g) + H2S(g)R-S-S-R(g) + 3H2(g) ➞2R-H(g) + 2H2S(g)sulfide can be converted tosulfur using the Claus process:6H2S(g) + 5O2(g) ➞2SO2(g) + 2S2(g) + 6H2O(g)4H2S(g) + 2SO2(g) ➞3S2(g) + 4H2O(g)abcdhot compressed airsuperheated water (at 170°C)molten sulfur and waterclayefghquicksandsandlimestonesulfur© Diagram Visual Information Ltd.● Hydrogen82PATTERNS—NON-METALSKey wordsallotropebonddiatomicmoleculeoxygenozonesulfurviscosityOxygen and sulfur:allotropes1 Allotrope of oxygenOxygenAllotropesO● Allotropesare different forms of thesame element in the same physicalstate.
Many elements, includingoxygen and su lfu r, exist as more thanone allotrope.OzoneOOOO1 OxygenOO++OO● Themost common form of oxygen is adiatom ic m olecu le, O2. The gas alsoexists as a triatomic molecule, O3,which is called ozon e.● Oxygen has two bon ds between theatoms. Each atom donates oneelectron to each bond.● In ozone, the central oxygen atomdonates a pair of electrons to form abond with the other two atoms.
Oneof the other atoms also donates a pairof electrons, while the other does not.OO–O–O2 Allotropes of sulfur2 Sulfur● Sulfurhas several allotropes in thesolid form, including rhombic sulfurand monocline sulfur.● Rhombic sulfur crystals have a lemonyellow appearance.● Monocline sulfur crystals are needlelike and have a deeper yellow color.● Each allotrope is composed of S8puckered molecular rings, butarranged in different ways.RhombicsulfurMonoclinicsulfur33 Heating sulfur© Diagram Visual Information Ltd.● Sulfurmelts when gently heated, andthe sulfur molecules are able to movearound, forming a low-viscosity liquid.● On stronger heating, the sulfur ringsbreak open, yielding sulfur molecules.These molecules join by cross-linking,causing a sharp increase in viscosity.● On even stronger heating, the crosslinked structure breaks, yielding smallsulfur molecules, which are freemoving, and the viscosity falls.StructureColorState of matterViscosityyellowyellowredblacksolidliquidliquidliquid–lowhighlow83Oxygen and sulfur:compound formation1 Oxygen and magnesiumPATTERNS—NON-METALSKey words2 Reaction of sulfur and ironMg2+Fe2+O2–S2–oxideoxygenperoxidesulfidesulfur1 Oxygen and magnesium● Oxygenreacts with most metals toform metal oxides.
Magnesium burnsin air with a bright flame, producing awhite smoke of magnesium oxide. Thereaction is even more vigorous in pureoxygen:abhydrogenhydrogenperoxidehydrogen sulfidemagnesium2Mg(s) + O2(g) ➞ 2MgO● Solublemetal oxides dissolve in waterto form alkaline solutions:Oxygen reacts withmagnesiunMagnesium oxideis ionicSulfur and ironglowIron sulfide isalso ionicMgO(s) + H2O(l) ➞ Mg(OH) 2(aq)2 Sulfur and iron● Su lfu r3 Phosphorous reacts with atmospheric oxygenhdgforms su lfides with manymetals.
When iron and sulfur areheated together, iron sulfide isformed:8Fe + S8 = 8FeS3 Oxygen and phosphorous● Oxygenalso reacts with non-metals toform oxides. Phosphorus burns in airto form phosphorus(V) oxide.Approximately 20 percent of the air isused:fcP4 (s) + 5O2(g) ➞ P4 O10 (s)e● Non-metalA tube full of aira oxgenb magnesium burningc volume scalePhosphorus is addedcm 3d 10 0of aire waterf stiff wireUnreacted phosphorusis left behindg phosphorus reactingh 79 cm 3 of air is left behindoxides dissolve in water toform acids:P4 O10 (s) + H2O(l) ➞ 4H3PO4 (aq)4 Other common reactions● Hydrogenburns in oxygen to formwater:4 Water, hydrogen peroxide, and hydrogen sulfide2H2(g) + O2(g) ➞ 2H2O(l)● HydrogenHOHOHOHHOHHOBaO2(s) + H2SO4 (aq) ➞H2O2(aq) + BaSO4 (s)SO● HydrogenHHSHWater is formed whenoxygen and hydrogenare exploded togetherHydrogen peroxide is madeby reacting a metalperoxide with acidHydrogen sulfide is madeby the reaction of a metalsulfide with dilute acidsu lfide is formed by thereaction of a metal sulfide with a diluteacid:FeS(s) + 2HCl(aq) ➞FeCl 2(aq) + H2S(g)© Diagram Visual Information Ltd.HHperoxide is formed by thereaction of metal peroxides, such asbarium peroxide, with dilute acids:84PATTERNS—NON-METALSThe oxides of sulfurKey wordscatalystlone pairoxidesulfitesulfur1 Laboratory preparation of sulfur dioxidesulfur dioxidesulfurous acidsulfur trioxideaSulfur oxides● Su lfu rcombines with oxygen to formtwo oxides: su lfu r dioxide (sulfur(IV)oxide) and su lfu r trioxide (sulfur(VI)oxide.1 Laboratory preparation ofsulfur dioxidecdb● Metalsu lfites, such as sodium sulfite,react with dilute acids to from sulfurdioxide:Na2SO3(s) + 2HCl(aq) ➞2NaCl(aq) + H2O(l) + SO2(g)● Sulfurdioxide is dried by passing itthrough anhydrous calcium chlorideand collected by downward delivery.● Sulfur dioxide dissolves in water toform su lfu rou s acid:2 Laboratory preparation of sulfur trioxideH2O(l) + SO2(g) ➞ H2SO3(aq)e2 Laboratory preparationof sulfur trioxideklf● Sulfurtrioxide is formed when drysulfur dioxide and oxygen are heatedin the presence of a platinizedasbestos catalyst:2SO2(g) + O2(g)h2SO3(g)● Sulfurtrioxide forms needle-likecrystals when cooled.● Sulfur trioxide dissolves in water toform sulfuric acid:igjH2O(l) + SO3(g) ➞ H2SO4 (aq)3 SO2 and SO3 molecules© Diagram Visual Information Ltd.● Insulfur dioxide, there are four pairsof bonding electrons and a nonbonding or lon e pair of electronsaround the sulfur atom.
The pairs ofelectrons are kept as far from eachother as possible by adopting a bentshape in which the double bondsbetween the sulfur and oxygen atomsare at an angle of 120°.● In sulfur trioxide, the three doublebonds form a trigonal planar structurearound the sulfur atom in which thebond angle is also 120°.abcdedilutesodium sulfiteanhydrous CaCl 2upward displacementoxygeni freezing mixture of ice andsaltj needles of sulfur oxidek to the fume cupboardl 3-way tapf sulfur dioxideg concentrated sulfuric acidfor dryingh plantinized asbestosO3 SO2 and SO3 moleculesOSO120 °OOSOSSOMolecule of sulfur dioxideOOMolecule of sulfur trioxide120 °O85Industrial preparation ofsulfuric acid (the contactprocess): theoryPATTERNS—NON-METALSKey wordscatalystexothermicequilibriumsulfursulfur dioxidesulfuric acidsulfur trioxide1 Sulfur burning∆H = –297 kJ mol –1S(1) + O2(g) → SO2(g)2 Conversion2SO2(g) + O2(g)2SO3(g)4 moles∆H = –192 kJ mol –12 molesSO2● Theindustrial preparation of su lfu ricacid is a three stage process:1.
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