Doc Brown's Chemistry Clinic

 Advanced Level Inorganic Chemistry Revision notes

(e.g. UK Advanced Level Chemistry GCE-AS-A2-IB US K12 grades ~11-12)

 The Periodic Table Part 10

Part 10d "3d block - Transition Metals" revision notes  1st draft

10d: Extra Data and extra hydroxide precipitate 'pictures'

 GCSE Chemistry revision notes * GCSE notes on Transition Metals * EMAIL query?comment

Part 10 3d block sub-index: 1. Introduction * 2. 3d-block data, general trends and character of Transition Metals * 3. Scandium * 4. Titanium * 5. Vanadium * 6. Chromium * 7. Manganese * 8. Iron * 9. Cobalt 10. Nickel * 11. Copper * 12. Zinc * 13. Other Transition Metals e.g. silver Ag or platinum Pt * Appendix 1. Acidity of hexa-aqua ions * Appendix 2. Complexes & ligands - the basics * Appendix 3. The shapes of complexes and isomerism * Appendix 4. Electron configuration and colour theory * Appendix 5. Redox equations, feasibility, calculating E^ø_reaction * Appendix 6. Catalysis - examples and theory * Appendix 7. Balancing redox equations * Appendix 8. Stability Constants of complex ions * Appendix 9. Colorimetry - quantitative analysis and determining the formula of a complex ion * Appendix 10. Preparation of complexes * Extra 3d block - Transition Metals data * Extra Hydroxide precipitate 'pictures' * Extra Electrode Potential Chart for 3d-block * Extra comparison of 3d-block formulae and oxidation states

Advanced Periodic Table Index * Part 1 A brief Periodic Table history * the modern Periodic Table * Part 2 Electronic structure of atoms : Spectroscopy and the H spectrum : Ionisation energies * Part 3 Period 1 survey : 1. Hydrogen : 2. Helium : Summary of  Period 1 : heavier element formation-stellar nuclear fusion  * Part 7 s-block metals Gps 1/2 Alkali/alkaline Earth Metals * Part 11 Group and Series data summaries and links to periodicity plots

Quick click to Introduction * Sc * Ti * V * Cr * Mn * Fe * Co * Ni * Cu * Zn * Ag/Pt etc.

Part 10d-1 DATA TABLE 2 - Extended SUMMARY FOR 3d BLOCK METALS

• 3d block data notes:
  1. na means 'not applicable' or 'not available'.
  2. The electronegativity values are from the Pauling scale.
  3. Ionic radii relate to the 'isolated' theoretical ion, NOT aqueous ions.
  4. Polarizing power is a measure of the ions charge density which has important chemical consequences e.g.
     • the bonding nature with non-metals e.g. ionic/covalent MCl_n
     • and the acidity of the hydrated aqueous ion [M(H₂O)₆]ⁿ⁺_(aq).
     • The charge density is equal to the ion charge divided by the volume of the ion (4∏r³/3).
     • Here the relative polarizing power of an ion is taken as the [unit ionic charge]/[ion radius(pm)]³ ratio, multiplied by 10⁶ to give a 'reasonable' number scale for easy comparison.
       • Some polarising power scales use the isolated ion charge divided by the radius.
     • Obviously, the larger the charge, or the smaller the volume or radius, the greater the charge density or polarising power.
     • Relative polarising power of Groups 1-3 ions for comparison with the 3d block ions above:

     • Group	ion	ion radius/pm	relative polarizing power	rpp (charge/radius)
       1	Na+	98	1.1	?
       2	Mg2+	78	4.2	?
       3	Al3+	60	13.9	?
       1	K+	133	0.4	?
       2	Ca2+	106	1.7	?

     • -
  5. -

Quick click to Introduction * Sc * Ti * V * Cr * Mn * Fe * Co * Ni * Cu * Zn * Ag/Pt etc.

Part 10d-2 A summary of some 3d-block compounds, complexes and oxidation states

Most are mentioned in the detailed individual element notes, but some have been added to illustrate other oxidation states you may not encounter on your course - but some good oxidation number practice!

Quick click to Introduction * Sc * Ti * V * Cr * Mn * Fe * Co * Ni * Cu * Zn * Ag/Pt etc.

Part 10d-3 Standard Electrode Potential Chart Diagram for the 3d-block elements

• Redox potential chart comments:

• All data quoted is for standard conditions i.e. 298K, 1 atm. pressure and 1 mol dm^-3 solutions of ions.

• Other than the solid metals, MnO₂ and FeO₄^2-, hydrogen gas, you assume all ions are in aqueous media.

• Unless an oxyanion, oxocation or another ligand in a complex is indicated, you assume you are dealing with hexaaqua-metal ions (H₂O ligand only).

• Further comments below draw out some general patterns and other points of interest.

  • All except scandium (Sc³⁺), which is not that reactive to acids despite the relatively negative M/M³⁺ potential, form a hydrated M²⁺ ion either by reaction of the metal with acid or reduction of a higher oxidation state complex-compound.

  • The stable oxidation states in aqueous solution containing dissolved oxygen from air are for the hydrated ions ...

    • (only Sc³⁺), [TiO]²⁺, VO²⁺, Cr³⁺, Mn²⁺, Fe³⁺, Co²⁺ and Ni²⁺ (only Zn²⁺).

    • On the basis of the electrode potential chart above, the argument is simple. In neutral or acid solution the oxidising potential of the oxygen-proton-water system is +1.23V. Therefore any e.g. M³⁺/M²⁺ potential less positive than +1.23V will result in the oxidation of the lower oxidation state species to the higher oxidation state species in the presence of dissolved oxygen which is reduced to water.

      • Oxidation states higher than the stable ones tend to oxidise water liberating oxygen and as mentioned above, lower oxidation states tend to be reducing and liberate hydrogen from water. So the Mn³⁺/Mn²⁺ and Co³⁺/Co²⁺ potentials lie above +1.23V so Mn³⁺ and Co³⁺ will oxidise water and cannot be stable in acid solution.

    • Note that the +4 oxidation states of Ti and V exist as hydrated oxo-cations because the high polarising power of the highly charged central metal ion causes deprotonation (see Appendix 1. Acidity of hexa-aqua ions).

    • The rest are [M(H₂O)_n]^2+/3+ where n is usually 6, can be 4 for Cu and Zn.

  • Apart from iron, there is a tendency for the lower oxidation state to become increasingly more stable with increasing atomic number.

  • Higher oxidation states which are normally oxidising in aqueous solution can be stabilised by complexing e.g. compare the Co(II)/Co(III) potential when complexed with water (+1.82V) and with the ligand ammonia (+0.10V).

  • There are classic examples of disproportionation where an intermediate oxidation state species spontaneously changes into a higher and lower' oxidation state species e.g.

    • Cu(I) ==> Cu(0) + Cu(II) and Mn(VI) ==> Mn(II) + Mn(VII).

    • These are described in detail, complete with electrode potential arguments for thermodynamic feasibility, under the respective metal.

  • -

Quick click to Introduction * Sc * Ti * V * Cr * Mn * Fe * Co * Ni * Cu * Zn * Ag/Pt etc.

Part 10d-4 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)

MUST X-CHECK ALL EQUATIONS and OBSERVATIONS IN THE NOTES

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 - amphoteric behaviour.

  • [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 consider it dissolving in mineral acids to form typical salts e.g. aluminium chloride, aluminium nitrate and aluminium sulphate.

    • Al(OH)_3(s) + 3HCl_(aq) ==> AlCl_3(aq) + 3H₂O_(l)

    • Al(OH)_3(s) + 3HNO_3(aq) ==> Al(NO₃)_3(aq) + 3H₂O_(l)

    • 2Al(OH)_3(s) + 3H₂SO_4(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) + 3CO₃^2-_(aq) ==> 2[Al(H₂O)₃(OH)₃]_(s) + 3CO_2(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) + CO₃^2-_(aq) ==> 2[Al(H₂O)₄(OH)₂]⁺_(aq) + CO_2(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.

Quick click to Introduction * Sc * Ti * V * Cr * Mn * Fe * Co * Ni * Cu * Zn * Ag/Pt etc.

GENERAL REVISION NOTES

SITE PURPOSE EDUCATION - online learning or 'self-private-tuition' using revision notes, quizzes, practice tests involving ADVANCED LEVEL CHEMISTRY in the areas of REVISING only the CHEMISTRY at Doc Brown's Chemistry Clinic via HOMEPAGE in secondary school/schools, 6th form college/colleges, academy/academies or home self-study and may help with 1st year undergraduate university chemistry courses. Hopefully it will encourage interest and understanding of Chemistry, Earth Science and Radioactivity in any country of the world, though the site is written entirely in English. The website is designed to help and unofficially support students/teachers revise-learn/teach the chemistry for modular or co-ordinated examination science courses from UK QCA based AQA, OCR (Oxford and Cambridge), Nuffield, Salters, Cambridge International (CIE), London International, WJEC, CCEA etc. Also, national award assessments-examinations for BTEC-NVQ applied, additional and chemistry science courses, Advanced Subsidiary Level GCE-AS-A2-IB-KS5-BTEC-NVQ exams. National Chemistry assessment levels, International Baccalaureate, K12 higher US grade level examinations for the national curriculum for secondary schools and colleges. The notes should also provide some background theory for a coursework assignment or project. BUT please note that my on-line revision notes and quizzes are no substitute for good classroom teaching-lecturing and thorough studying of your own notes and textbooks, practicing past papers and a copy of the syllabus which are readily downloaded from the examination board sites, but I hope here and there they will lend a tutoring hand on some topic, unit, module etc. For final revision you have to be intellectually honest about what you don't know or follow, YOU have to take the stuff to pieces, analyse what you do/do not understand and reconstruct it so it all makes sense in the end. There is no other way, there are no magic secrets on how to revise and learn, its mainly down to hard work and just good old fashioned study and employing teach-yourself strategies without the need for extra tutors and tutoring lessons. I also think there is too much hit and miss revision using past papers (which I do NOT supply) and not enough systematic revision. I also hope it will help teachers in planning lessons and developing schemes of work for science-chemistry. There are no lesson plans on the site but there are plenty of quizzes to incorporate into classroom activities whether photocopied or on electronic whiteboard projector for use as self-tuition-assessment purposes and a variety of teaching and learning styles and the images may be used in Microsoft Word documents and powerpoint projections. The site seems to be used by a large number of home study tutors, particularly the revision notes. An individual tutor may print out the notes for science-chemistry learning teaching-tuition purposes and for background material for assignments and projects. I have no interest or time in producing WORD.doc or xxxx.pdf files of the notes at the moment. Neither have I time to write up many practical laboratory experiments ('lab'-'labs') at the moment, but the notes contain lots of background information of chemical reactions in terms of observations-balanced equations-reactants-products-theory etc. I also find it difficult to recommend specific exam websites or syllabus textbooks, it depends exactly on what you need, what you have time for, and there are so many of them to choose from and I do not supply past examination papers. Dr W P Brown GCE A AS A2 IB Advanced-Subsidiary Level Chemistry 25-09-07