无机化学课件：25 Titanium Vanadium Chromium

1、Titanium (Ti)Electron Configuration4s23d24s23d13d23d1AppearanceHard; lustrous silver colored.Sources: (Named the titans)Ilmenite: FeTiO3Rutile: TiO2 Brilliant white, commonly used as a pigment.Titanite: CaTiSiO5Perovskite: CaTiO3UsesResistant to corrosion, lightweight and strong.Alloys, machinery, a

2、ircraft, and missiles.Bright white pigment TiO2.ChemistryMain oxidation state: +4(d0). Other oxidations states: -1(d5), 0, +2 & +3.Burns in air and is the only element that burns in nitrogen. It is ductile only in an oxygen-free atmosphere. Resistant to dilute hydrochloric and sulfuric acids, most o

3、rganic acids, chlorine gas and chloride solutions. Reaction of titaniumwith airTitanium metal is coated with an oxide layer that usually renders it inactive. However once titanium starts to burn in air it burns with a spectacular white flame to form titanium dioxide, TiO2 and titanium nitride, TiN.

4、Titanium metal even burns in pure nitrogen to form titanium nitride.Ti(s) + O2(g) TiO2(s)2Ti(s) + N2(g) TiN(s)with waterTitanium metal is coated with an oxide layer that usually renders it inactive. However, titanium will react with steam form the dioxide, titanium(IV) oxide, TiO2, and hydrogen, H2.

5、Ti(s) + 2H2O(g) TiO2(s) + 2H2(g)with acidsDilute aqueous hydrofluoric acid, HF, reacts with titanium to form the complex anion TiF63- together with hydrogen, H2.2Ti(s) + 12HF(aq) 2TiF63-(aq) + 3H2(g) + 6H+(aq)Titanium metal does not react with mineral acids at ambient temperature but does react with

6、 hot hydrochloric acid to form titanium(III) complexes.Reaction of titanium continuedwith the halogensTitanium does react with the halogens upon warming to form titanium(IV) halides. The reaction with fluorine requires heating to 200C. So, titanium reacts with fluorine, F2, chlorine, Cl2, bromine, I

7、2, and iodine, I2, to form respectively titanium(IV) halides.Ti(s) + 2F2(g) TiF4(s) whiteTi(s) + 2Cl2(g) TiCl4(l) colourlessTi(s) + 2Br2(g) TiBr4(s) orangeTi(s) + 2I2(g) TiI4(s) dark brownPreparation of TiKroll ProcessTiO2 + 2C + 2Cl2 TiCl4 +2CO2FeTiO3 + 7Cl2 + 6C 2TiCl4 + 2FeCl3 + 6COTiCl4 + 2Mg Ti

8、 + 2MgCl2Electrolysis:TiO2 (solid, cathode) = molten salt electrolysis in CaCl2 = Ti (cathode) + O2 (anode)Chemists have two ways to pry metal from an oxide ore. One, electrolysis, decomposes the ore into its elementary constituents with electricity. Aluminum manufacturing employs this method. The a

9、lternative, called chemical reduction, involves reacting the ore with a substance that has a greater affinity for oxygen than the metal to be extracted. This procedure is used to refine iron MetallurgyTiCl4TiCl4 + HCl(c) H2TiCl6Ziegler-Natta CatalystTiCl4 + (CH3CH2)3AlTiCl4 + 2H2O TiO2 + 4HClPartial

10、 hydrolysis: TiOCl2Polyethylenemost popular plastic. Grocery bags, shampoo bottles, toys, etc.Simple structure than all polymers.Branched/low-density = (LDPE) Easier to makeLinear/high-density = (HDPE)Ziegler-Natta CatalystH2CCH2CH2CH2n manufacture of TiO2Reaction of TiO2rutile(金红石), anatase(锐钛矿), b

11、rookite(板钛矿), rutile is the most common form, and the others transform into it on heating.TiCl4(g) + O2(g) TiO2(s) + 2Cl2(g) 1200 oC, Cl2(g) recycleTiO2 + H2SO4 (c) TiOSO4 + H2O no titanyl cation TiO2+, probably Ti(OH)2(H2O)42+2KOH + TiO2 K2TiO3 + H2OamphotericTESTS FOR TITANIUMAqueous solutions con

12、taining titanium(IV) give an orange-yellow color on addition of hydrogen peroxide; the color is due to the formation of peroxo-titanium complexes, but the exact nature of these is not known.Vanadium (V)Electron Configuration: 4s23d33d43d33d2Origin: Named after the Scandinavian goddess Vanadis becaus

13、e of its beautiful multi-coloured compounds. .Ores:Vanadinite: Pb5Cl(VO4)3Patronite: VS4Roscoelite: K2V4Al2Si6O20(OH)4Carnotite: K2(UO2)2(VO4)2.H2OPropertiesSoft, ductile, bright white.Main oxidation states: III, IV, & VUsesAbout 80% of the vanadium produced is used as a steel additive. In this form

14、 it produces one of the toughest alloys for armor plate, axles, piston rods and crankshafts. Less than 1% of vanadium and as little chromium make steel shock- and vibration-resistant.Vandium(V) oxide is used in ceramicsVanadiumit is not very useful itselfmost of the metal produced is in the form of

15、an alloy ferrovanadium, containing between 40 and 90% vanadium. This is added to steel to produce a very tough high-speed steel.Ferrovanadium is obtained by reduction of the oxide V2O5 with ferrosilicon” (Fe + Si).The pure metal is very difficult to prepare because it combines even more readily with

16、 hydrogen, carbon, nitrogen and oxygen than does titaniumOxides of Group 5B metalsOxidation state+5+4+3+2VV2O5VO2V2O3VONbNb2O5NbO2-NbOTaTa2O5TaO2-(TaO)V2O5: an essentially acidic oxide, dissolving in alkalis to give vanadates; however, addition of acid converts the anionic vanadate species to cation

17、ic species:V2O5 (yellow) + H+ VO2+ (pale yellow) + H2ORedox ReactionsSulphur dioxide will reduce V(+5) to V(+4) only; zinc in hydrochloric acid will reduce V(+5) step by step to V(+2). The half equations and the overall equation is given for each of these reactions.The aqueous chemistry of vanadium(

18、V) is complex and depends on pH. Here we take strongly acidic solutions in which the yellow ion VO2+ is the species present. The colour changes for the complete reduction sequence are: +5 +4 +3 +2 yellow bluegreenlavenderVO2+VO2+V(H2O)63+ V(H2O)62+The water ligands are not shown in the equations bel

19、ow, but remember that they are there for V(+3) and V(+2).+5 +4with aqueous SO2: 2VO2+(aq) + 4H+(aq) + 2e 2VO2+ (aq) + 2H2O (l)SO32 (aq) + H2O (l)SO42 (aq) + 2H+(aq) + 2e (aq)2VO2+(aq) + SO32 (aq) + 2H+(aq) 2VO2+ (aq) + SO42 (aq) + H2O (l) with zinc in HCl: 2VO2+(aq) + 4H+(aq) + 2e 2VO2+ (aq) + 2H2O

20、(l)Zn(s)Zn2+ (aq) + 2e 2VO2+(aq) + 4H+(aq) + Zn(s) 2VO2+ (aq) + Zn2+ (aq) + 2H2O (l) Redox Reactions Continued+4 +3 with zinc in HCl 2VO2+ + 2e + 4H+ (aq)2V3+ (aq) + 2H2O (l)Zn(s)Zn2+ (aq) + 2e 2VO2+ + Zn(s) + 4H+ (aq) 2V3+ (aq) + Zn2+ (aq) + 2H2O (l) +3 +2 with zinc in HCl 2V3+(aq) + 2e 2V2+ (aq)Zn

21、(s)Zn2+ (aq) + 2e 2V3+(aq) + Zn(s)2V2+ (aq) + Zn2+ (aq)TESTS FOR VANADIUMthe reduction of vanadium(V) to vanadium(II) by zinc and acid, gives a very characteristic test for vanadium. Addition of a few drops of hydrogen peroxide to a vanadate(V) gives a red colour (formation of a peroxo-complex)Chrom

22、ium (Cr)Electron configuration: 4s13d53d53d43d3Ore: Chromite FeCr2O4Properties:Hard, silvery metal with a blue tinge. Capable of taking a high polish. Metal-metal quadruple bonds are possible.Gives Ruby its color.Main oxidation state: IIIUses:Used in stainless steels (13% Cr) in increase corrosion r

23、esistance. Used for plating other metals.Used chemically in pigments (vivid green, yellow, red and orange colors). Tanning agents, catalysts, and oxidizing agents.Chromium compounds are toxic.CHROMIUMPure MetalDirect reduction of chromate by heating with carbon and calcium oxide gives an alloy of ir

24、on and chromium, ferrochrome, which can be added to steel, to make stainless steel (12-15 % chromium).Chromium Compounds All compounds of chromium are colored (except Cr(CO)6 ?); the most important are the chromates of sodium and potassium and the dichromates and the potassium and ammonium chrome al

25、ums. The dichromates are used as oxidizing agents in quantitative analysis, also in tanning leather. Other compounds are of industrial value; lead chromate is chrome yellow, a valued pigment. Chromium compounds are used in the textile industry as mordants, and by the aircraft and other industries fo

26、r anodizing aluminum.Chromium(III) halides FormulaColorMPM-X (pm)CrF3green1404190CrCl3red-violet1152238CrBr3green-black1130257CrI3black500d-Preparations:CrX3 are prepared from Cr with X2, dehydration of CrCl3.6H2O requires SOCl2 at 650 CAnhydrous Chromium(III) chloridepeach-coloured solid,the reacti

27、on of chlorine with a heated mixture of chromium(III) oxide and carbon:the reaction of sulfur dichloride oxide with the hydrated chloride:hydrated chloride, CrCl3,6H2OGreen colored crystalCrIII(H2O)4Cl2+Cl-.2H2O.grey-bluepale greengreenAgNO3Chromium(II) halides FormulaColorMPm (BM)CrF2green8944.3CrC

28、l2white820-8245.13CrBr2white844-CrI2red-brown868Preparations:Reduction of CrX3 with H2/HX gives CrX2Chromium oxides FormulaColorOxidation StateMPMagnetic MomentCrO3deep redCr6+197d-Cr3O8-intermediate-Cr2O5-Cr5O12etc-CrO2brown-blackCr4+300d-Cr2O3greenCr3+2437-antiferromagnetic 35 COxidesBy heating ch

29、romium(III) hydroxideBy heating ammonium dichromate:green powder, insoluble in water and in acids (cf. aluminum oxide, Al2O3). It is not reduced by hydrogen.In 1986 the initial drying of the dichromate in a rotary vacuum drier, resulted in a serious explosion in Ohio. The cause was not obvious but t

30、he presence of an organic contaminant must be a possibility.Prep：Prop：(greyish green)(green)1.Cr2O32.Cr(OH)3CHROMIUM(III) HYDROXIDE, Cr(OH)3(HYDRATED)3224342CrClO,12HKCr(SOSOCr ），）（Common salts of Cr()Hydrolysis+HOCr(OH)(HOCr(H252362）410-As reducing agentAs Oxidizing AgentBlueZn)(2Cr22+Zn(s)Cr3+ Cr2

31、+(aq) Cr3+(aq)14H6SOOCrOH7OS32Cr24272Ag22823+-+O8H2CrO2OHO3H2Cr(OH)224224+-V33.1)Cr/OCr(3272=+-Acidic：EV12.0)Cr(OH)/CrO(-424-=-Basic：EColor of Cr() Coordination CompdspH effectpH6：CrO42- majorOHOCr 2HCrO 2H2CrO2272424+-+-(yellow)(orange)2.Interchange between Cr2O72- and CrO42-Solubility Effect-=10.0

32、2)OCr(Ag7722-=101.1)CrO(Ag1242+-+2H)(s,CrO2AgOHOCr4Ag422272brick+-+2H)(s,2BaCrOOHOCr2Ba422722lemon+-+2H )(s,2PbCrOOHOCr2Pb422722yellowK2Cr2O7 PbCrO4 3. Cr2O72- as OxidantO7H2KCl2+721.33V)/CrO(Cr32=+-OH4Cr23SOH83SOOCr232423272+-+-O7H2Cr3S8HS3HOCr232272+-O7H2Cr3I14H6IOCr232272+-2CrCl3Cl)14HCl(s)OCrK32

33、722+ cO7H2Cr6Fe14H6FeOCr2332272+-O7H2Cr3Sn14H3SnOCr2342272+-Dichromate and chromateDichromate and chromate equilibria is pH dependent: HCrO4- - CrO42- + H+ K=10-5.9H2CrO4 - HCrO4- + H+ K=10+0.26Cr2O72- + H2O - 2HCrO4- K=10-2.2HCr2O7- - Cr2O72- + H+ K=10+0.85Dichromate preparationSodium dichromate is

34、 prepared on the large scale by heating powdered chromite with sodium carbonate, with free access of airConversion from chromate to dichromate:2 CrO42-(aq) + 2 H+ (aq) Cr2O72-(aq) + H2O (l)lower pH: Cr3O102-, Cr4O132-, CrO3. Strong oxidizing agent.Polymerization. stronger in oxyacids of Mo and W. polymetallates 多酸 e.g. Mo36O1128-, H2W12O4210- etc.HeteropolymetallatesCoIIW12O406-, NiIVMo9O326-, etc.Heterogeneous catalyst.Zeolite Linde A: Na12(Al2Si12O48).27H2O Similar behavior for some main group compounds:aluminosilicateChromium (II) Acetat