Recognition of nichel

Nickel is sought to fourth analytic group as Ni 2+. It is precipitated as sulphide insoluble at pH 9.8 for ammonium / ammonia buffer. The precipitating reagent is Na 2 S (preferable to TAA and ammonium sulfide).

sulfide of nickel

In reality, the nickel and cobalt are not searched as sulphides. They are searched directly in the solution coming from the third analytical group . This solution is at pH 8-9 for ammonium / ammonia buffer.

The nickel if present is in the form of complex or tetra amino hexacoordinate → Ni (NH 3) 6 2+ or Ni (NH 3) 4 2+.

Nickel recognition

Remember that the solution from the third analytical group is divided in two. In a portion are searched cobalt and nickel, zinc and manganese in the other.

-Reazione Of Tschugaeff

We must make sure that the pH of the solution from the third group is actually post 8-9. A pH more alkaline, given by an excess of ammonia, mean low concentration of Ni 2+ "free" (because complexed by ammonia).

At the rate in which the search nickel are added 2-3 drops of dimethylglyoxime (alcoholic solution). If this Ni 2+ forms a flocculent precipitate cherry red.

Overall nickel dimethylglyoxime

The precipitate is formed because the nickel-dimethyl gliossima whole is more stabila nickel-ammonia complex. The complex is however soluble in acid environment, as you can see from the stoichiometry of the reaction.

In fact, even the cobalt forms a complex with dimethylglyoxime. The complex is rust colored and soluble. This is usually used an excess of reagent (dimethylglyoxime), so as to delineate a cherry red precipitate (insoluble complex of nickel) in the field rust (soluble complex of cobalt).

* (See → search of cobalt )

The search of the nickel is also carried out from the solution in which it is precipitated as a salt of the cobalt Fischer (cobaltinitrito or potassium). This solution (after centrifuging and removed the yellow precipitate cobaltinitrito) is made alkaline with soda. If this Ni 2+ precipitates Ni (OH) 2, nickel hydroxide, a precipitate by the evident apple green color. For further confirmation, and thoroughly washed after separating the precipitate, it can be treated with bromine water. Br 2 oxidized Ni (OH) 2 Ni (OH) 3, of brown color.

Warning: the English translation of this article must be completed.

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