Metal Cation Identification
M A N G A N E S E
| PROJECT CODE:
|| METAL CATION IDENTIFICATION
| PROJECT TITLE:
||ID of MANGANESE Cations by Precipitation Reactions
| RELEASE DATE:
|| 9 JULY 1998
| LAST UPDATE:
| VERSION HISTORY:
|| 1.0, 1.1 ( Context updates)
V2.0 ( Text and formatting update - Sep-2009)
This is an account on how to detect Manganese ions in solution by simple precipitation reactions. Manganese is not so easy to distinguish since many of its compounds are white precipitates or does not form a ppt at all. However, with The following set of tests it will be easy to confirm Manganese without requiring complex procedures or sophisticated equipment.
As mentioned, the tests are simple precipitation reactions. A solution of a Manganese salt (Manganese 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 Manganese insoluble compound or formation of a complex since Manganese is a transitional metal.
Mn++ X (aq) + 2 Na+ Y- (aq) ===> Mn++ 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 Manganese, since other metal salts can give the same results. The verification of 4 or 5 such tests will be enough to confirm Manganese in an unknown sample.
In 10ml testtubes, 4mls of Manganese 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 Manganese salt of which 16 produced a valuable result. These are marked with an Y in the React Column .
a) A WHITE/CREAM-PEACH ppt was formed which did not dissolved on xs.
b) On standing a characteristic brown ring at the surface exposed to air, and browning at the sides of the test tube (where the ppt is in contact with air taks place. c) No particular change on heating
The insoluble white hydroxide was precipitated. This is oxidized by air to a manganese (hydorxide) having a higher oxidizing state.
a) Similarly to the NaOH, a WHITE/CREAM ppt which gets a brownish tinge where it is in direct contact with air.
b) No reaction on heating.
Manganese Hydroxide was precipitated by Ammonia
a) A PURE WHITE ppt which is not oxidised to a brown compound on standing in air, as did the hydroxide.
b) Heat had no effect on the ppt.
Precipitation of Manganese Carbonate.
a) No rection initially
b) A faint white ppt was formed on heating strongly.
Can be considered as a negative test, since not so much ppt was formed.
a) A FLESH BROWN ppt was formed immediately
b) No further reactions on heating, or standing out.
Manganese Sulphide was ppted at once.
a) A GELATINOUS WHITE ppt was formed.
b) On heating, no colour changes seem to happen.
The insoluble Manganese phosphate was precipitated out.
a) Initially a GELATINOUS WHITE PPT was formed,
b) On heating the ppt intensified to a CREAM WHITE colour.
Manganese Borate was precipitated. Perhaps some degree of oxidation has taken place on heating.
a) No reaction
b) On heating strongly, just some brown ppt was formed
This is yet another test which is considered as a negative result
a) A GELATINOUS CREAM/LIGHT BROWN ppt was formed.
b) No further reaction on heating or standing.
Insoluble Manganese Silicate was precipitated.
a) A MILKY WHITE ppt was formed
b) On heating no reaction took place.
Another straight forward precipitation
a) This resulted in MUDDY BROWN ppt
b) On heating + standing no further reaction took place.
a) The solution turned to a clear yellow colour, and on standing for few minutes a brown ring was formed at the surface of the solution
b) On heating a faint Yellow/Light Brown ppt was formed.
Very strange reaction. erhaps a very slow ppt type of reaction.
a) A Dark Brown ppt was immediately formed. When filtered a clear solution + the drk brown ppt was obtained. Hence all the permangante have reacted rapidly.
b) No further reaction on heating.
This is a great test for Manganese ions, as the permanganate rarely forms ppts. It is also strange that a manganese forms a ppt with the Permanganate anion (same element in cation + anion!)
a) A THICK WHITE ppt was formed
b) No further changes on heating.
a) No colour change apart from the solution turned from colourless/pink to clear yellow solution.
b) No particular change on heating.
Not quite an indicative test!?
a) No reaction initially, even upon adding xs BiSelenite
b) On heating strongly a WHITE ppt was formed.
The white Manganese selenite ppt was formed on heating
Manganese is a transitional metal, but which unlike most metals of this family, it does not form many coloured ppt or complex solutions
It forms a white ppt with the Ammonium Hydroxide and Sodium Hydroxide
(insoluble in xs) which turns to a brown ppt on contact with air. This is already a quite good indication of the presence of Manganese.
Thus is obviously not enough, hence further confirmatory tests are required. The ones which stand out are that with the Permanganate producing a dark brown precipitate and the muddy brown ppt produced with the Potassium Ferri(III)Cyanide solution. Also the milky white ppt with Ferri(II)Cyanide will help to exclude many suspected metals, such as Fe3+.
Unfortunately there are no other unique tests for Manganese.
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