Reactions of the Metals of the Copper Group.

67. Metals whose sulphides are insoluble in HCl and are precipitated in presence of that acid by the group reagent H2S.

Mercury, Lead, Bismuth, Copper, Cadmium, Arsenic, Antimony, and Tin.

SUB-GROUP A.-Sulphides of the above metals insoluble in (NH4)2S1⁄2, viz., Mercury, Lead, Copper, Bismuth, and Cadmium.

MERCURY. Hg, c.w. 200. Mercuric Salts.

1. H2S produces, when added by degrees, first a white precipitate, which changes to orange, then to brownish red, and finally to a black precipitate of HgS. These successive changes of colour on the addition of HS are exceedingly characteristic. This precipitate is insoluble in HCl and in HNO3, even on boiling; it is soluble, however, in KHS and in aqua regia.

2. KHO produces a yellow precipitate of HgO, which is insoluble in excess of the precipitant, except when added to very acid solutions.

3. (NH)HO produces in solutions of HgCl, a white precipitate of HgCl(NH), ("white precipitate").

4. SnCl, produces, when added in small quantities, a white precipitate of HgCl2, but on adding an excess of the reagent, metallic mercury precipitates as a grey powder, and may be united into a coherent globule by boiling with HCI.

5. Reactions 5 and 6 for mercurous salts (64) are also produced with mercuric salts.

68. LEAD. Pb, c.w. 207.

1. H2S produces a black precipitate of PbS, even in solutions of PbCl2, so that a weak solution of a lead salt which has not been precipitated with HCl will be precipitated with H2S. Hence lead occurs both in the silver and copper groups.

2. Reactions 2, 3, 4, and 5, for lead, in Group I. (65), are also applicable in this group.

69. BISMUTH. Bi, c.w. 210.

1. HS produces a black precipitate of BigS, insoluble in KHS and KHO, but soluble in HNO3.

2. KHO or (NH4)HO produces a white precipitate, which on boiling becomes yellow (Bi2O3); the precipitate is insoluble in excess of either reagent.

3. H2O, when added in considerable quantity to normal salts of bismuth, produces an immediate white precipitate of a basic salt of bismuth.

Bismuth trichloride is most easily precipitated by H2O. If another salt of this metal is being examined, it is best to precipitate the oxide first by ammonia;

dissolve it in as little HCl as possible, and evaporate it almost to dryness. On adding water to this solution, a precipitate of BiOCl at once forms, which is insoluble in tartaric acid (compare corresponding reaction with antimony, 74, 4). Solutions of bismuth salts containing much free acid do not give this reaction with H2O until the excess of acid has been expelled by evaporation.

4. K2CrO4 produces a yellow precipitate of Bi2(CrO4)3, soluble in HNO3, and insoluble in NaHO. (Compare reaction for lead, 65, 3.)

5. Heated on charcoal with NaHCO, in the reducing flame of the blow-pipe, yields brittle metallic globules; also a slight yellow incrustation of oxide on the charcoal.

70. COPPER. Cu, c.w. 63°5.

1. H2S produces a black precipitate of CuS, soluble in HNO3, but insoluble in KHS, and only slightly soluble in (NH4)2S2. CuS is also dissolved by KCN, but is insoluble in hot dilute H2SO4

2. KHO produces a pale blue precipitate of Cu(HO)2, insoluble in excess of the precipitant. If the KHO be added in excess and the mixture boiled, the precipitate becomes black and loses water.

3. (NH4)HO produces, when added in small quantities, a greenish blue precipitate of a basic salt, soluble in excess to a dark blue solution, which consists of a double basic salt of copper and ammonium.

4. K4Fe(CN)。 produces a brown precipitate of

Cu,Fe(CN)6, insoluble in dilute acids, but decomposed by KHO.

5. Fe precipitates copper in the metallic state, from its solutions, especially in presence of a little free acid. The iron ought to be bright and clean.

6. Zn also precipitates copper solutions. If a solution of copper containing a few drops of HCl be placed in a platinum capsule, and a fragment of zinc added, the copper will be precipitated on the platinum as a red coating.

7. Compounds of copper, when heated in the Bunsen lamp flame, impart a green colour to it, especially after addition of AgCl.

8. Mixed with NaHCO3 + KCN and heated on charcoal before the reducing blow-pipe flame, yields bright red metallic particles, soluble in HNO, and giving a deep blue solution on adding (NH)HO.

71. CADMIUM. Cd, c.w. 112.

1. H,S produces a yellow precipitate of CdS, soluble in HNO3, but insoluble in KHS, in (NH4)2S, and in KCN. CdS is dissolved by hot dilute H2SO4. (Compare reaction for copper, 70, 1.)

2. KHO produces a white precipitate of Cd(HO)2 insoluble in an excess of the precipitant.

3. (NH4)HO also precipitates Cd(HO)2, but the precipitate is soluble in excess.

4. Heated on charcoal with NaHCO, in the reducing blow-pipe flame, yields no metallic bead, but a brown incrustation of CdO.

RESIDUE.