Cations Group IIIB

For the separation of Group IIIB cations two methods are described. The first... 

Table V.24 Separation of Group IIIB cations with the hydrochloric acid-hydrogen peroxide method The ppt. may contain CoS, NiS, MnS, and ZnS. Wash well with lper cent NH4C1 solution to which 1 per cent by volume of (NH4)2S has been added reject the washings. Transfer the ppt. to a small beaker. Add 5 ml water and 5 ml 2m HC1, stir well, allow to stand for 2-3 minutes and filter (1).

Table V.25 Separation of Group IIIB cations with the hydrochloric acid-potassium chlorate-hydrogen peroxide method The ppt. may contain CoS, NiS, MnS, and ZnS. Wash well with 1 per cent NH4C1 solution to which 1 per cent by volume of yellow ammonium sulphide solution has been added reject the washings. Transfer the ppt. to a porcelain basin, add 5 ml water and 5 ml concentrated HC1 and stir for 2-3 minutes. If a black residue is obtained, the presence of NiS and CoS is indicated if complete dissolution takes place, only small amounts of Ni and Co are likely to be present. Evaporate the mixture to 2-3 ml in the FUME CUPBOARD, add 4 ml concentrated HN03 (1) and concentrate to 2-3 ml. If the solution is not clear, dilute with 8-10 ml water, filter off the sulphur and return the filtrate to the porcelain basin in the fume cupboard. Boil down to 1-2 ml, taking great care not to evaporate to dryness. Add 5 ml concentrated HN03 and evaporate again to 1-2 ml (2).

VI.14 SEPARATION AND IDENTIFICATION OF GROUP IIIB CATIONS ON THE SEMIMICRO SCALE The separation scheme outlined in Table VI. 16 commences with the sulphide precipitates obtained according to the prescriptions of the general separation table (Table VI. 11 in Section VI.9). It is a semimicro adaptation of the hydrochloric acid-hydrogen peroxide method, described in Table V.24 (Section V.15). 

Table VI.16 Separation of Group IIIB cations on the semimicro scale The ppt. may contain CoS, NiS, MnS, and ZnS. If it is not black, CoS and NiS are absent. Stir the ppt. in the cold with 1 ml of M HQ (1 volume of concentrated acid 10-12 parts of water) for 1-2 minutes. Centrifuge.

Table VII.7 Separation of Tl from the rest of Group IIIB cations Dissolve the precipitate in 2m HN03. Expel H2S by boiling, add H2S03 and expel excess S02 again by boiling. Pour the solution into an excess of saturated Na2C03 solution. Filter.

Under the appropriate conditions, the heavier members of the groups IIIB-VIB elements will form a wide variety of interesting cluster compounds called Zintl anions. Some of these contain a group lA element as the cation The main group anion clusters in this class of compounds generally follow normal rules of valence, and most are semiconducting. All require the presence of an easily oxidizable element, such as those of the groups lA and IIA, in their formation. 

Munze (19) has used a Born-type equation to calculate stability constants of In(III) and An(III) complexes of carboxylates as well as other ligands which agreed well with experimental values. His approach was modified by allowing the dielectric constant to be a parameter (the "effective" dielectric constant, De) in an analysis of fluoride complexation by M(II), M(III) and M(IV) cations (20). A value of De = 57 was found satisfactory to calculate trivalent metal fluoride stability constants which agreed with experimental values for Ln(III), An(III) and group IIIB cations (except Al(III). Subsequently, the equation was used... 

Table 5.8 Separation of Group IIIB cations (contd.)...

If this test is positive, remove phosphate (see Table 5.6 in Section 5.8). Among the less common ions, titanium, zirconiiun, cerium, thorium, and uranium will be completely precipitated by ammonia solution, and will therefore appear together with the other Group IIIA cations. Vanadium will only partly be precipitated here some of the vanadium present will be found in the filtrate of the sulphide precipitates of Group IIIB cations. Some of the thallium(I) partly removed with Group I will also appear in this Group some molybdenum will appear in the filtrate of Group IIIB sulphides. 

V.10 SEPARATION OF GROUP II CATIONS INTO GROUPS IIA AND IIIB Having precipitated the sulphides of the Group II cations (cf. Section V.8, Table V. 12) the next task is to separate these into Groups IIA (Hg2+, Bi3+, Pb2+, Cu2+ and Cd2+) and IIB (As3+, As5+, Sb3+, Sb5+, Sn2+, Sn4+). There are two methods recommended for the purpose, one making use of (yellow) ammonium polysulphide, the other making use of potassium hydroxide. 

Table VII1.4 Removal of phosphate ions before precipitating the Group III cations Boil the filtrate from Group II until free from H2S, add a few drops concentrated HN03 (or 1-2 ml bromine water) and boil gently for 1 minute. Test a small portion for phosphate with ammonium molybdate and nitric acid, and a further portion for the presence of Groups IIIA, IIIB, IV, or Mg by the addition of NH4C1 and NH3 solution. If both tests are positive, proceed as follows.

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