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A level inorganic chemistry: 3d block-transition metal complex ions & hydroxide precipitates

Periodic Table - Transition Metal Chemistry - Doc Brown's Chemistry  Revising Advanced Level Inorganic Chemistry Periodic Table Revision Notes

 Appendix 12 Complex and hydroxide precipitate 'pictures'

Some 'test tube' pictures of a variety of soluble transition metal complex ions and precipitates of insoluble complexes.

(c) doc b GCSE/IGCSE Periodic Table Revision Notes

(c) doc b GCSE/IGCSE Transition Metals Revision Notes

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB KS5 A/AS GCE advanced level inorganic chemistry students US K12 grade 11 grade 12 inorganic chemistry - 3d block transition metal chemistry Sc Ti V Cr Mn Fe Co Ni Cu Zn

INORGANIC Part 10 3d block TRANSITION METALS sub–index: 10.1–10.2 Introduction 3d–block Transition Metals * 10.3 Scandium * 10.4 Titanium * 10.5 Vanadium * 10.6 Chromium * 10.7 Manganese * 10.8 Iron * 10.9  Cobalt * 10.10 Nickel * 10.11 Copper * 10.12 Zinc * 10.13 Other Transition Metals e.g. Ag and Pt * 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, Eø * 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

Advanced Level Inorganic Chemistry Periodic Table Index * Part 1 Periodic Table history * Part 2 Electron configurations, spectroscopy, hydrogen spectrum, ionisation energies * Part 3 Period 1 survey H to He * Part 4 Period 2 survey Li to Ne * Part 5 Period 3 survey Na to Ar * Part 6 Period 4 survey K to Kr and important trends down a group * Part 7 s–block Groups 1/2 Alkali Metals/Alkaline Earth Metals * Part 8  p–block Groups 3/13 to 0/18 * Part 9 Group 7/17 The Halogens * Part 10 3d block elements & Transition Metal Series * Part 11 Group & Series data & periodicity plots * All 11 Parts have their own sub–indexes near the top of the pages

Appendix 12 PICTURES of PRECIPITATES and COMPLEX FORMATION

Prior to, and with, excess reagent for selected 3d block aqueous ions.

They can be used as simple tests for identifying transition metal ions.

Text and formula summary of these reactions of 3d block ions is given below but there are more details in most cases in the notes for each metal for ...

[M(H2O)6]n+ where M = metal, n = 2 or 3 and Al3+ for comparison (See Chemical Tests for more precipitates)

... and many are useful simple tests to identify metal ions (ppt. = precipitate, gel. = gelatinous)

Reagent\Ion and initial colour Cr3+(aq)

green

 Mn2+(aq) very pale pink ~ colourless Fe2+(aq)

pale green

 Fe3+(aq)

yellow–brown

 Co2+(aq)

pink

 Ni2+(aq)

green

 Cu2+(aq)

blue

 Zn2+(aq)

colourless

 Al3+(aq)

colourless
initial NaOH(aq)

strong base/alkali

 green gel. ppt. of

Cr(OH)3

 white gel. ppt. but darkens with oxidation

Mn(OH)2 ==> Mn2O3  ==> MnO2

 dark green ppt.  => brown on oxidation

Fe(OH)2 ==> Fe(OH)3

 brown gel. ppt. of

Fe(OH)3

 blue gel.  ppt. that turns pink on standing

Co(OH)2

 green gel. ppt. of

Ni(OH)2

 gel. blue ppt. of

Cu(OH)2

 white gel.  ppt. of

Zn(OH)2

 white gel.  ppt. of

Al(OH)3
excess NaOH(aq)

strong base/alkali

 ppt. dissolves to give clear green solution of complex ion

[Cr(OH)6]3–

 no further effect – just as above with more oxidation no further effect – just as above with more oxidation no further effect – just as above with more oxidation no further effect no further effect There is a slight reaction, a deeper blue colour is seen, but, the hydroxide precipitate is effectively insoluble. See Copper Notes ppt. dissolves – clear solution, colourless complex ion

[Zn(OH)4]2–

 ppt. dissolves – clear solution, colourless  complex ion

[Al(OH)6]3–
initial NH3(aq)

weak base/alkali

 green gel. ppt. of

Cr(OH)3

 white ppt. darkens with oxidation from O2

Mn(OH)2 ==> Mn2O3 ==> MnO2 

 dark green ppt. turns brown – oxidation

Fe(OH)2 ==> Fe(OH)3

 brown gel. ppt. of

Fe(OH)3

 blue gel. ppt. that turns pink on standing

Co(OH)2

 green gel. ppt. of

Ni(OH)2

 gel. blue ppt. of

Cu(OH)2

 white gel. ppt. of

Zn(OH)2

 white gel. ppt. of

Al(OH)3
excess NH3(aq)

weak base/alkali

 dissolves – clear green solution of complex ion

[Cr(NH3)6]3+

 no further effect no further effect no further effect ppt. dissolves – clear brown solution of complex ion

[Co(NH3)6]2+

 dissolves – clear pale blue solution of complex ion

[Ni(NH3)6]2+

 ppt. dissolves to give clear blue solution of complex ion

[Cu(NH3)4(H2O)2]2+

 ppt. dissolves – clear colourless solution of

[Zn(NH3)4]2+

 no further effect
adding of Na2CO3(aq)

weak base/alkali

 green gel. ppt. +  bubbles

Cr(OH)3 + CO2

 white ppt. that darkens with oxidation

MnCO3 ==> Mn2O3  ==> MnO2

 dark green ppt. turns brown – oxidation

Fe(OH)2 ==> Fe(OH)3

 brown gel. ppt. + bubbles

Fe(OH)3 + CO2

 blue gel. ppt. that turns pink on standing

Co(OH)2 + CoCO3

green gel. ppt of

Ni(OH)2 + NiCO3

 gel. blue–turquoise ppt.

Cu(OH)2 + CuCO3

 white gel. ppt of

Zn(OH)2 + ZnCO3

  white gel. ppt. + bubbles

Al(OH)3+ CO2
Reagent/Ion and initial colour Cr3+(aq)

green

 Mn2+(aq) very pale pink ~ colourless Fe2+(aq)

pale green

 Fe3+(aq)

yellow–brown

 Co2+(aq)

pink

 Ni2+(aq)

green

 Cu2+(aq)

blue

 Zn2+(aq)

colourless

 Al3+(aq)

colourless

For detailed equations of these reactions go to the specific chemistry sections for that metal via the index below

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

 

The comparison equations for the aluminium ion (NOT a 3d block metal)

  • The addition of limited amounts of the bases sodium hydroxide or ammonia solution to an aluminium salt solution.

    • [Al(H2O)6]3+(aq) + 3OH–(aq) ==> [Al(H2O)3(OH)3](s) + 3H2O(aq)

    • A white gelatinous precipitate of aluminium hydroxide is formed.

      • Simplified equation: Al3+(aq) + 3OH–(aq) ==> Al(OH)3(s)

  • The further addition of excess sodium hydroxide or ammonia solution.

    • With excess ammonia there is no effect, but with excess sodium hydroxide the aluminium hydroxide dissolves to form a soluble aluminate complex anion – therefore exhibiting amphoteric behaviour. since the hydroxide will also dissolve in acids (paragraph below NaOH equation).

    • [Al(H2O)3(OH)3](s) + 3OH–(aq) ==> *[Al(OH)6]3–(aq) + 3H2O(aq)

      • Simplified equation: Al(OH)3(s) + 3OH–(aq) ==> *[Al(OH)6]3–(aq)

      • *The products will be an equilibrium mixture including [Al(H2O)2(OH)4]–(aq) and [Al(H2O)(OH)5]2–(aq) too.

      • You could write the equation in terms of forming these species too and any of the three possibilities should get you the marks.

    • To complete the 'amphoteric' picture of aluminium hydroxide we consider it dissolving in mineral acids to form typical salts e.g. aluminium chloride, aluminium nitrate and aluminium sulfate.

      • Al(OH)3(s) + 3HCl(aq) ==> AlCl3(aq) + 3H2O(l)

      • Al(OH)3(s) + 3HNO3(aq) ==> Al(NO3)3(aq) + 3H2O(l)

      • 2Al(OH)3(s) + 3H2SO4(aq) ==> Al2(SO4)3(aq) + 6H2O(l)

  • The addition of sodium carbonate solution to an aluminium salt solution.

    • Bubbles of carbon dioxide and a white gelatinous precipitate of aluminium hydroxide are formed.

      • 2[Al(H2O)6]3+(aq) + 3CO32–(aq) ==> 2[Al(H2O)3(OH)3](s) + 3CO2(g) + 3H2O(aq)

      • There several equation 'permutations' to represent this quite complicated reaction, so I've just composed one that shows the formation of both observed products. Since sodium carbonate solution is alkaline you can legitimately write a hydroxide ppt. equation as for sodium hydroxide above but it doesn't show the formation of carbon dioxide.

        • You can write an equation to show the formation of carbon dioxide leaving a soluble cationic complex of aluminium in solution and this equation fits in well with the acid–base nature of this reaction.

          • [Al(H2O)6]3+(aq) + CO32–(aq) ==> 2[Al(H2O)4(OH)2]+(aq) + CO2(g) + 3H2O(aq)

          • This equation shows the hexaaquaaluminium ion acting as a Bronsted–Lowry acid donating two protons to the carbonate ion (B–L base) to form carbon dioxide and water.

      • This reaction shows why 'aluminium carbonate' 'Al2(CO3)3' cannot exist. The hydrated highly charged central metal ion is too acidic to co–exist with a carbonate ion. The same situation applies to the chromium(III) Cr3+ and iron(III) Fe3+ ions i.e. no chromium(III) carbonate or iron(III) carbonate exists. However with a lesser charged, lesser acidic ion, carbonates can exist, so there is an iron(II) carbonate FeCO3.

  • The addition of excess sodium carbonate solution has no further effect. Sodium carbonate is too weak a base to effect the amphoteric nature of aluminium hydroxide and dissolve the aluminium hydroxide precipitate.

 

 Doc Brown's Advanced Level Chemistry Revision Notes

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, Eø * 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

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