CHEMISTRY : Metal Cation Identification

N I C K E L

INTRODUCTION:

This is an account on how to detect Manganese ions in solution by simple precipitation reactions. Manganese is quite easy to distinguish since many of its precipitates (mainly greenish) it forms. With the following set of tests it will be easy to confirm Nickel without requiring complex procedures or sophisticated equipment.

PRINCIPLE

As mentioned, the tests are simple precipitation reactions. A solution of a Nickel salt (Nickel Ammonium Sulphate) was mixed with an equal ammount of another solution, in which a physical change is noted, usually a colour change due to a precipitation of the Nickel insoluble compound or formation of a complex since Nickel is a transitional metal.

Ni++ X (aq) + 2 Na+ Y- (aq) ===> Ni++ Y (s) + 2 Na+ X- (aq)
(s) Solid precipitate forming a colour change in soultion

One type of reaction is not enough, to confirm the presence of Nickel, since other metal salts can give the same results. The verification of 4 or 5 such tests will be enough to confirm Nickel in an unknown sample.

PROCEDURE

In 10ml testtubes, 4mls of Nickel solution was placed. To this, about 2mls of solution of the following compounds all having different anions (-ve) was added. If desired, the mixture was heated gently to increase rate of reaction or added in exess to detect further complex reactions, usually the dissolving of the ppt just formed.

The following compounds were mixed with the Nickel salt of which 13 produced a valuable result. These are marked with an Y in the React Column .

RESULTS

01: Sodium Hydroxide

a) A PISTACCIA LIGHT GREEN ppt was formed which did not dissolved on xs. c) No particular change on heating

The insoluble green hydroxide was precipitated out.

02: Ammonium Hydroxide

a) No precipitation, but the colour changes from green to CLEAR VIOLET BLUE No change on adding xs ammonia.

b) No reaction on heating. A complex transitional reaction have taken place, forming [ Ni(NH3)6 ] 2+

03: Sodium Carbonate

a) A CREAM LIGHT GREEN ppt was formed.

b) Heat had no effect on the ppt. Precipitation of Nickel Carbonate.

04: Sodium Sulphite (or Sodium Metabisulphite)

a) No rection initially

b) A GREY GREEN ppt was formed on heating strongly. Only on heating the Grey Green Nickel Sulphite was ppt.

05: Sodium Sulphide

a) A THICK BLACK ppt was formed immediately, insoluble in xs.

b) No further reactions on heating, or standing out. Nickel Sulphide was ppted at once.

06: Ammonium Phosphate

a) A GELATINOUS LIGHT GREY GREEN ppt was formed.

b) On heating, no colour changes seem to happen. The insoluble Nickel Phosphate was precipitated out.

07: Sodium Tetraborate

a) Initially, no reaction was formed,

b) On heating a CLOUDY WHITE/GREEN ppt was formed. Nickel Borate was precipitated on heating. Very slow reaction since not so much ppt was formed.

08: Sodium Methanoate

a) No reaction

b) On heating strongly, just some GREEN ppt was formed

This test which considered as a negative result, or a very slow reaction which does not give valuable results.

09: Sodium Silicate

a) A LIGHT GREEN ppt was formed

b) No further reaction on heating or standing. Insoluble Nickel Silicate was precipitated.

10: Potassium Ferro(II)Cyanide

a) A GREEN-CYAN ppt was formed

b) On heating the ppt turned to a more GREENISH colour

Another straight forward precipitation

11: Potassium Ferri(III)Cyanide

a) This resulted in an ORANGE/BROWN ppt

b) On heating + standing no further reaction took place. Precipitation reaction

12: Sodium Tungstate

a) A WHITE, LIGHT GREEN ppt was formed

b) No further changes on heating. Nickel Tungstate precipitated

13: Sodium Biselenite

a) No reaction initially, even upon adding xs BiSelenite

b) On heating strongly a little cloudy ppt was formed. Propably a false indicative result since very little ammount of ppt was deposited.

CONCLUSION

Nickel is a transitional metal, but which unlike most metals of this family, it does not form many coloured ppt or complex solutions

It is first identified by the LIGHT GREEN ppt formed with Sodium Hydroxide (insoluble in xs) and with Sodium Carbonate. An important test is that with Ammonia sol., which results in no precipitate but a unique BLUE VIOLET solution. This distinguishes very good from the suspect of the green ppt produced by Fe2+ ions.

Most of the reactions available are in the greenish colour (Phosphate, Silicate, Borate), but the black ppt with the Sulphide, Rusty Brown ppt with Ferro(III)Cyanide, and the CYAN GREEN ppt with the Ferro(II)Cyanide are good tests to identify the presence of Nickel.

Unfortunately there are no other unique tests for Nickel although the above are just enough.

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