10.4. Chemistry of Titanium Ti, Z=22, 1s²2s²2p⁶3s²3p⁶3d²4s² 

data comparison of titanium with the other members of the 3d–block and transition metals

Extended data table for TITANIUM

• Extraction of titanium

  • Titanium ore is mainly the oxide TiO₂, which is converted into the tetrahedral shaped covalent liquid titanium tetrachloride TiCl₄ by heating with carbon and chlorine. There is no change in oxidation state of titanium in this reaction (+4 in both compounds involved)

  • The chloride is then reacted with sodium or magnesium to form titanium metal and sodium chloride or magnesium Chloride.

  • This reaction is carried out in an atmosphere of inert argon gas so non of the metals involved becomes oxidised by atmospheric oxygen.

  • TiCl₄ + 2Mg ==> Ti + 2MgCl₂ or TiCl₄ + 4Na ==> Ti + 4NaCl

  • Overall the titanium oxide ore is reduced to titanium metal (overall O loss, oxide => metal) and the magnesium or sodium acts as a reducing agent.

• Uses of TITANIUM

  • Titanium is a hard silvery–white lustrous metal of relatively low density.

  • Titanium is relatively resistant to corrosion and is a very important metal for various specialised uses.

  • Titanium carbide, TiC, is used in making extremely hard alloys for high speed tools e.g. the drill bit.

  • Titanium alloys are amongst the strongest and lightest of metal alloys.

    • There is a GCSE/IGCSE note about the bonding and structure of alloys on another page.

  • It is used in aeroplanes, in nuclear reactor alloys, chemical reactor vessels and for replacement hip joints.

  • With a lighter density of 4.4 g/cm³ compared to steel (~7.9 g/cm³) its just as strong as steel and with the added advantage of being unreactive towards oxygen and water at room temperature so does not suffer the rusting of iron corrosion.

  • Titanium(IV) oxide, TiO₂, is an important white pigment used in the paints industry.

    • Note that Ti⁴⁺ has a [Ar]3d⁰ structure, hence, with no 3d electrons it is colourless (see colour theory).

  • Titanium(IV) oxide is also used in paper making, ceramics and textile industries.

  • Titanium(IV) chloride and other covalent titanium compounds are used as polymerisation catalysts (e.g. Ziegler–Natta catalysts) for manufacturing polyalkenes like poly(propene).

The Chemistry of TITANIUM

• Titanium extraction and Ti(IV) CHEMISTRY

• It is more difficult  to extract from its ore than other more common metals so is not cheap!

  • Titanium is extracted from the raw material rutile ore which contains titanium dioxide. This is a high melting ionic compound Ti⁴⁺(O^2–)₂.

  • Carbon reduction of the oxide to the metal is not that practical due to titanium carbide formation so the titanium(IV) oxide is initially converted to titanium(IV) chloride which is then reduced to the metal with a more reactive metal in a displacement reaction.

    • Tungsten (W), another transition metal, cannot be obtained from reduction of its oxide for the same reason.

  • The rutile titanium oxide ore is heated with carbon and chlorine to make titanium(IV) chloride

    • TiO₂ + 2Cl₂ + C ==> TiCl₄ + CO₂

  • After the oxide is converted into TiCl₄ which is then reacted with sodium or magnesium to form titanium metal and sodium chloride or magnesium Chloride. The sodium and magnesium act as the reducing agent in this batch process.

    • This reaction is carried out in an atmosphere of inert argon gas so non of the metals involved becomes oxidised by atmospheric oxygen.

      • TiCl₄ + 2Mg ==> Ti + 2MgCl₂  or  TiCl₄ + 4Na ==> Ti + 4NaCl

    • These are examples of metal displacement reactions e.g. the less reactive titanium is displaced by the more reactive sodium or magnesium.

    • Overall the titanium oxide ore is reduced to titanium metal (overall O loss from ox. state +4, oxide => metal with ox. state 0)

    • TiCl₄ is covalent liquid which (i) hydrolyses back to the oxide in water , BUT (ii) dissolves in conc. hydrochloric acid to form the hexachlorotitanate(IV) complex ion.

      • (i) TiCl_4(l) + 2H₂O_(l) ==> TiO_2(s) + 4HCl_(aq/g) (fumes in air!)

      • (ii) TiCl_4(l) + 2Cl^–_(aq) ==> [TiCl₆)]^2–_(aq) (typical complex anion)

  • When titanium(IV) compounds are dissolved in water of acid the oxo–cation [TiO]²⁺ is formed.

• The electrode potential chart highlights the values for various oxidation states of titanium.

• TITANIUM(III) CHEMISTRY

• Titanium(III) compounds can be obtained from Ti(IV) salts by using a zinc/dil. sulphuric acid reduction agent.

  • eg the colourless oxotitanium(IV) ion is reduced to the purple hexaaquatitanium(III) ion

  • colourless Ti(IV) as [TiO]²⁺ ==> Ti(III) in acid solution giving the purple [Ti(H₂O)₆)]³⁺_(aq).

  • but it is readily oxidised back to Ti(IV) by dissolved oxygen from the atmosphere (see electrode potential chart TiO²⁺/Ti³⁺ +0.10V is less positive than O₂+H⁺/H₂O +1.23V in acid solution).

  • Titanium(III) chloride TiCl₃ is a violet solid.

• TITANIUM(II) CHEMISTRY

• Titanium(II) chloride TiCl₂ is a black solid.

• The violet hexaaquatitanium(II) ion [Ti(H₂O)₆)]²⁺ ion can be formed by reducing Ti(IV) or Ti(III) with a metal/acid mixture but it is very unstable in redox terms, ie readily oxidised by dissolved oxygen from the atmosphere.

• Ti²⁺, a powerful reducing agent, will reduce water to hydrogen (i.e. oxidised by water to Ti³⁺) and because it is rapidly oxidised by air it cannot exist in aqueous solution.

  • From the electrode potential chart you can see that the electrode potential of Ti³⁺/Ti²⁺ is –0.37V and is less positive than electrode potential O₂/H⁺/H₂O +1.23V in acid solution.

• Comparison of titanium with a typical Group 4 metal e.g. tin

  • Tin only exhibits oxidation states of +2 and +4, there is no intermediate +3 compounds.

  • Tin compounds are usually colourless.

  • Physically, tin is a much weaker metal with much lower melting/boiling point than titanium.

• Summary of some complexes–compounds & oxidation states of titanium compared to other 3d–block elements

• –

Scandium * Titanium * Vanadium * Chromium * Manganese * Iron * Cobalt * Nickel * Copper * Zinc * Silver & Platinum

keywords redox reactions ligand substitution displacement balanced equations formula complex ions complexes ligand exchange reactions redox reactions ligands colours oxidation states: titanium ions Ti2+ Ti3+ Ti4+ Ti(+2) Ti(II) Ti(+3) Ti(III) Ti(+4) Ti(IV) TiCl4 + 2Mg ==> Ti + 2MgCl2 or TiCl4 + 4Na ==> Ti + 4NaCl TiO2 + 2Cl2 + C ==> TiCl4 + CO2 TiCl4 + 2Mg ==> Ti + 2MgCl2 or TiCl4 + 4Na ==> Ti + 4NaCl TiCl4 + 2H2O(l) ==> TiO2 + 4HCl TiCl4 + 2Cl–(aq) ==> [TiCl6)]2– [Ti(H2O)6)]3+ [Ti(H2O)6)]2+ Ti3+/Ti2+ oxidation states of titanium, redox reactions of titanium, ligand substitution displacement reactions of titanium, balanced equations of titanium chemistry, formula of titanium complex ions, shapes colours of titanium complexes

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Alphabetical Index for Science Pages Content A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Scandium * Titanium * Vanadium * Chromium * Manganese * Iron * Cobalt * Nickel * Copper * Zinc * Silver & Platinum

Introduction 3d–block Transition Metals * Appendix 1. Hydrated salts, acidity of hexa–aqua ions * Appendix 2. Complexes & ligands * Appendix 3. Complexes and isomerism * Appendix 4. Electron configuration & colour theory * Appendix 5. Redox equations, feasibility, E^ø * Appendix 6. Catalysis * Appendix 7. Redox equations * Appendix 8. Stability Constants and entropy changes * Appendix 9. Colorimetric analysis and complex ion formula * Appendix 10 3d block – extended data * Appendix 11 Some 3d–block compounds, complexes, oxidation states & electrode potentials * Appendix 12 Hydroxide complex precipitate 'pictures', formulae and equations