Separation and identification of Group IIB cations

For the separation of Group II cations into Groups IIA and IIB two methods were suggested (cf. Section V.10, Tables V.14 and V.15). To separate and identify the Group IIB cations, one of the two recommended procedures must be followed, according to the method chosen in the previous step. If the ammonium polysulphide method (method a) has been followed in Section V.10, then method (a) has to be applied here. Method (b), on the other hand, has to be used if the potassium hydroxide method was followed to separate Groups IIA and IIB. 

Transfer the ppt. to a small conical flask, add 5-10 ml concentrated HC1 and boil gently for 5 minutes (with funnel in mouth of flask). Dilute with 2-3 ml water, pass H2S for 1 minute to reprecipitate small amounts of arsenic that may have dissolved, and filter (3). 

Dissolve the ppt. in 3-4 ml warm dilute NH3 solution, filter (if necessary), add 3-4 ml 3 % H202 solution and warm for a few minutes to oxidize arsenite to arsenate. Add a few ml of the Mg(N03)2 reagent. 

Stir and allow to stand. White, crystalline ppt. of Mg(NH)4)As04, 6H20. 

Filter off ppt., and pour 1 ml of AgN03 solution containing 6-7 drops of 2m acetic acid on to residue on filter. Brownish-red residue of Ag3As04 (4). 

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VI.12 SEPARATION AND IDENTIFICATION OF GROUP IIB CATIONS ON THE SEMIMICRO SCALE For this separation the centrifugate from Group IIA is used. The separation scheme outlined in Table VI. 14 is therefore linked directly to Table VI in Section VI.11. If the ammonium polysulphide method has been adopted for the separation of Groups IIA and IIB, the student should scale down the scheme given in Table V.18 (Section V.12) to semimicro scale. 

The separation and identification of Group IIB cations can be carried out by following the prescriptions given in Table VII.4. 

Table VII.4 Separation and Identification of Group IIB cations in the presence of Pt, Au,...

VL11 SEPARATION OF GROUPS IIA AND IIB AND SEPARATION AND IDENTIFICATION OF GROUP IIA CATIONS When describing these separations in macro scale, two alternative methods have been suggested (see Section V.10), one being based on the use of ammonium polysulphide (see Table V.14) and the other on potassium hydroxide (Table V.15). In semimicro scale the potassium hydroxide method is more suitable and this will be presented here. This does not mean however that the ammonium polysulphide... 

VII.14 SEPARATION AND IDENTIFICATION OF GROUP II CATIONS IN THE PRESENCE OF MOLYBDENUM, GOLD, PLATINUM, PALLADIUM, SELENIUM, AND TELLURIUM The first step in this separation process is to separate cations into Groups IIA and IIB. 

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