An introductory course of lessons and exercises in chemistry (rewritten 1919) by Schoch Eugene Paul 1871-

Author:Schoch, Eugene Paul, 1871- [from old catalog]
Language: eng
Format: epub
Tags: Chemistry
Publisher: [Austin] The Chemical laboratory of the University of Texas
Published: 1919-03-25T05:00:00+00:00

10. Effects Produced by the Addition of Ammonium Chloride and Ammonia to Solutions of Salts of Common Metals.

Na% K + , Ca + + , Sr + + , Ba + + :—no effect whatever because the hydroxides of these metals are strong bases.

Ag + :—forms a ppt. of AgCl, which is dissolved by ammonia to form Ag(NH 3 ) 2 Cl. This compound tends to dissociate into its original constituents—

Ag(Jm,) ,C1 ^± AgCl-f-2HN 3 ,

and it is stable only in the presence of free NH 3 . Hence, when the excess of N~H, in these solutions is neutralized by the addition of an acid to the mixture, the insoluble AgCl is obtained again.

Pb + + :—forms a ppt. of PbCl 2 , and this is changed by ammonia to Pb(OH)Cl, an insoluble white compound.

Hg + :—forms a ppt. of Hg 2 Cl 2 , and this is changed by ammonia to a Hack, insoluble mass, admixture of mercury and of the compound HgCl NH 2 , according to the equation:

Hg 2 CL+2NH 4 0H=HgClNH,,+NH 4 C]+Hg+2H 2 0.

Hg + + :—gives, on the addition of ammonia, HgClNH 2 , a white compound insoluble in water. Treated with HC1, it forms HgCl.+NHjCl, which are soluble.

Cu + + , Cd + + , Zn + + , M + + :—they form soluble compounds of the general formula M(KrL) 4 Cl 2

Or M(NH 3 ) 4 S0 4 .

The cations of these salts are: Cu(NH 3 ) 4 ++ , Cd(NH 3 V + , Zn(NH 3 ) 4 ++ , M(M ; ) 4 ++ . With colored salts—such as those of Cu + + and Ni + + —the formation of the complex ions shows itself by a great deepening of the color.'

The ammonia compounds tend to dissociate into their original constituents—

Cu(NH,) 4 S0 4 ±^CuS0 4 +l:NH 3 ,

and they are stable only in the presence of free NTE 8 . Hence when the excess of NH 3 in these solutions is neutralized by the addition of an acid, the original simple salts (e. g., CuS0 4 , in the illustration above) are obtained again.

Fe + + and Mn + + :—these cations are not affected directly by N"H i Cl-j-NH 4 0H, but in alkaline solutions they exert a great tendency to change to the trivalent form—Fe + + + and Mn ++ + — hence on contact with the air, these mixtures turn dark and gradually form precipitates of Fe(OH).. and Mn(OH) 3 , respectively, because the change to the trivalent form is brought about by the oxygen of the air, according to the equation:— 2Fe(OH) 2 -fO+H,0=2Fe(OH) 3 .

Mg + + :—not affected by NH 4 C1+NH 4 0H.

Bi + * + . Fe + + + . A1 + + + :—theso ions are precipitated completelv as hydroxides, Bi(OH) 3 , Fe(OH) 3 , A1(0H) 3 .

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