Qualitative tests on First Row Transition Metal Ions.

For these exercises, you will be assigned two T.M. ions on which you will perform some simple tests. This is best done in a series of test tubes using small samples (1 or 2 mg or the amount needed to cover the tip of a small spatula). In most cases, the absence of a colour change will signify that no reaction has taken place, however this should NOT be taken for granted. Record all observations as they occur directly in your laboratory notebook.
In addition, you should answer the following questions:

        1). What are the principal minerals and how is the metal isolated?
        2). In which biological species does the metal occur?
        3). What are the principal industrial applications?

Titanium

        a) Take a small quantity of TiO2 and suspend it in a few cm3 of H2O. Divide the suspension and to one half add a saturated solution of KOH. Dilute the solution. To the other half, carefully drop in some concentrated H2SO4. Dilute the solution. Note and explain your observations. Test each solution with H2O2.

For the remainder of the tests, prepare a solution of TiCl3 by diluting 2 cm3 to 20 cm3.

        b) Add a few drops of 30% H2O2 to a small quantity of your Ti(III) solution. Finally add some NaOH solution to this. Note and explain your observations.

        c) To a few cm3 of the Ti(III) solution, add some bench ammonia solution. Leave the resulting suspension to stand for 10 minutes. Note and explain your observations.

        d) Repeat this using NaOH instead of the ammonia. Note and explain your observations.

        e) Decant off the mother liquor from the product of c) above and wash the precipitate with water, discard the washings. Carefully add concentrated H2SO4 to your residue. Carefully add the resulting solution to an equal volume of H2O2. Note and explain your observations.

        f) To a few cm3 of solution e) add some Zn dust and a few cm3 of dilute H2SO4. Note and explain your observations.

Vanadium

         a) Place a small amount (the end of a spatula) of ammonium meta-vanadate in a silica crucible and heat gently until no further changes occur. Note and explain your observations.

        b) Once your silica crucible has cooled, add 10 cm3 of 3M NaOH to the solid and transfer the suspension to a small flask. Wash the crucible with a further 10 cm3 of 3M NaOH and add the washings to the flask. Warm the flask gently to ensure complete dissolution of the solid. Slowly add 3M HCl from a burette to the solution. Note and explain your observations.

        c) Place one spatula load of ammonium meta-vanadate in a small flask and add 5 cm3 of dilute H2SO4. Note and explain your observations.

        d) Decant off the liquor from c) above and wash your solids with water, discarding the washings. Transfer your solid to a silica crucible and cover it with oxalic acid. Gently heat the mixture. Note and explain your observations.

        e) Once the fusion mixture from d) has cooled, add dilute HCl and transfer the suspension to a small flask. Make the solution up to 20 cm3 with dilute HCl and slowly add dilute NaOH dropwise. Note and explain your observations.

        f) To the final solution from e) above, add a small quantity of K2S2O8 and then acidify with dilute HCl. Note and explain your observations.

Chromium.

        a) Dissolve a spatula load of K2Cr2O7 in dilute HNO3. Slowly add to this dilute NaOH. Note and explain your observations.

        b) Add bench BaCl2 to an acidified solution of K2Cr2O7. Repeat using an alkaline solution of K2Cr2O7. Note and explain your observations.

        c) Mix a small quantity of K2Cr2O7 with a spatula load of KCl. Carefully add concentrated H2SO4 (in the fume cupboard). Note and explain your observations.

        d) Dissolve a small quantity of chrome alum in 20 cm3 of dilute HCl and cool the solution in ice. Slowly add 40 cm3 of dilute NaOH from a burette. Note and explain your observations. What do you understand by the term olation.

         e) Repeat d), but add a spatula load of sodium oxalate to the acidified solution before you begin adding the base. Note and explain your observations.

        f) Dissolve 2 g of chrome alum in 40 cm3 of cold water (do not heat). Divide the solution into two parts. Heat one of these solutions to 70 C, until the colour changes. Cool to room temperature and then add 20 cm3 of 0.2 M Pb(NO3)2. Stir and then allow the precipitate to settle. To the unheated solution, add 20 cm3 of 0.2 M Pb(NO3)2. Estimate which solution produces the more precipitate. Note and explain your observations.

Manganese.

        a) Dissolve a small quantity of Na2C2O4 in water and add a few drops of concentrated H2SO4 (carefully). Add a drop of dilute KMnO4. Gently heat the solution. Note and explain your observations.

        b) Dissolve a small quantity of Na2C2O4 in water using just enough H2SO4 to effect solution. Warm to 60 C and then without stirring, slowly add dropwise KMnO4. Note and explain your observations.

        c) Dissolve a small quantity of MnSO4 in dilute H2SO4 and carefully add 10 drops of concentrated H2SO4. To this add 5 drops of 0.1 M (approximately) KMnO4. Note and explain your observations.

        d) Add concentrated HCl to:
i) solid KMnO4 ii) solid MnO2. Note and explain your observations.

        e) Dissolve a small quantity of MnSO4 in dilute H2SO4 and then slowly add a dilute solution of NaOH. Note and explain your observations.

Iron

        a) To separate dilute solutions of FeCl3,
add: i) KSCN ii) K3{Fe(CN)6} iii) K4{Fe(CN)6}. Note and explain your observations.

        b) Repeat a) above, using an iron(II) solution instead of iron(III). Note and explain your observations.

        c) To a dilute solution of FeCl3, add solid NaF and then a few drops of a dilute solution of KSCN. Note and explain your observations.

        d) To a dilute solution of FeCl3, slowly add dilute NaOH. Repeat this test but add some NaF before adding the NaOH. Note and explain your observations.

        e) Repeat d) using an iron(II) solution. Note and explain your observations.

        f) To a dilute solution of FeCl3, add some NaI and a few drops of CCl4. Note and explain your observations.

        g) Prepare a solution of I3-. Add a few drops of this to a solution of iron(II) and warm gently. Add some CCl4. Once all reactions appear to be completed, acidify with dilute H2SO4. Note and explain your observations.

Cobalt

        a) Make a dilute aqueous solution of CoSO4. To this, slowly add dilute ammonia and finally concentrated NH3. Note and explain your observations.

        b) Carefully add 3% H2O2 to half the solution from a) above. Dilute the resulting solution with water. Make up the other half of the solution above to the same volume with water. Note and explain your observations.

        c) To a dilute solution of CoSO4, carefully add 3% H2O2. Note carefully any changes. Slowly add NH3 to your resulting solution. Note and explain your observations.

        d) To a dilute solution of CoSO4, carefully add dilute NaOH. To the resulting suspension add pellets of NaOH. Note and explain your observations.

        e) Carefully add 3% H2O2 to the resulting suspension from d). To a separate portion of CoSO4 solution, add 3% H2O2 and then dilute NaOH. Note and explain your observations.

        f) To a dilute solution of CoSO4, slowly add solid NaCl. Repeat using concentrated HCl instead. Dilute the resulting solutions with water. Note and explain your observations.

Nickel

        a) To a dilute solution of Ni(II), slowly add 3 M NaOH. Is the solid formed soluble in excess base? Note and explain your observations.

        b) To the suspension from a) above, slowly add a small quantity of K2S2O8. Note and explain your observations.

        c) To a dilute solution of Ni(II), slowly add a few cm3 of bench ammonia. Once the reaction appears to be complete, add concentrated ammonia. Note and explain your observations.

        d) To the solution resulting from c) above, add a small quantity of K2S2O8. Once the reactions are complete, slowly add NaOH solution. Note and explain your observations.

        e) To a dilute solution of Ni(II), slowly add concentrated HCl. Note and explain your observations.

        f) What is the structure of Ni(DMG)2? Is this a common stereochemistry for Ni(II)? Draw the d orbital splitting diagram which accounts for the diamagnetism of this compound.

Copper

        a) To a dilute solution of Cu(II), slowly add concentrated HCl. To the resulting solution add solid NH4Br. Note and explain your observations.

        b) To a dilute solution of Cu(II), slowly add concentrated ammonia. To this solution add a small piece of filter paper. Note and explain your observations.

        c) To a dilute solution of Cu(II), slowly add 4M NaOH. Heat gently the resulting suspension. Note and explain your observations.

        d) To a dilute solution of Cu(II), slowly add a solution of KI. Add a few drops of CCl4 and shake. Slowly add an aqueous solution of Na2S2O3 until the reaction has completed. Note and explain your observations.

        e) To a dilute solution of Cu(II), add a few cm3 of tartaric acid. Slowly add an aqueous solution of NaOH. Adjust the quantities of tartrate and OH- until no precipitate remains. Add a small quantity of glucose and warm gently. Decant the mother liquor and wash the solid with water. Note and explain your observations.

        f) To the solid from e) above, add concentrated HCl and then slowly add NaOH. Note and explain your observations.

References

Comprehensive Inorganic Chemistry
Chemistry of the Elements, Greenwood and Earnshaw
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