HW Lab 25 Group II

HW Lab 25 Group II - Lab 25 Group II Prelab Questions: Use...

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Lab 25 Group II Prelab Questions: Use Discussion information starting p.59 1) Basis of separation a) Group II ions form insoluble sulfides from acidic solution (p.50)(after they are oxidized to their highest oxidation state by the nitric acid) b) Basic solution (3 M NaOH): Sulfides in the copper subgroup are insoluble but sulfides in the antimony subgroup are soluble because they are amphoteric.(p.53) c) Lead forms an insoluble sulfate upon the addition of sulfuric acid while sulfates of bismuth and copper are soluble.(p53) d) Bismuth forms an insoluble hydroxide upon the addition of ammonia while copper hydroxide does not form due to the preferential formation of the copper ammonia complex ion which is soluble (p.54) 2) Purpose of procedure a) Oxidizing agent (see 1a above) b) To make sure the yellow ppt is not simply (BiO) 2 CrO 4 (s) which is also yellow and does in fact contain PbCrO 4 . The lead chromate will dissolve in in the presence of hydroxide but the bismuth compound will not.(p54) c) Stannite ion, Sn(OH)) 3 - , is easily oxidized by oxygen to stannate ion, Sn(OH) 6 2- , and there is a disproportionation rxn that can also occur upon standing. (p55) d) Oxalic acid is added because the tin oxalato complex is more stable and will stay in solution while the antimony oxalato complex can be converted to the antimony sulfide with the addition of thioacetamide.(p56) e) The iron will reduce the antimony to its elemental form (black solid) and also reduce tin(IV) to tin(II).(p57) 3) Reagent Solid Ion in Solution a) 9 M H 2 SO 4 PbSO 4 Cu 2+ b) 3 M NaOH Bi 2 S 3 Ni 2+ c) Thioacetamide CuS Ni 2+ d) PbS Zn 2+ e) Cold dilute HCl AgCl Sn 2+ f) Thioacetamide SnS 2 Fe 2+ g) 15 M NH 3 Bi(OH) 3 Cu(NH 3 ) 4 2+ h) Thioacetamide Sb 2 S 5 Al 3+ 4) Confirmation a) Pb 2+ Confirming Reagent
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This note was uploaded on 04/29/2008 for the course CHEM 123 taught by Professor Larosa during the Spring '06 term at Ohio State.

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HW Lab 25 Group II - Lab 25 Group II Prelab Questions: Use...

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