CHEMISTRY :
Metal Cation Identification
I R O N
| PROJECT CODE: |
02.0x |
| SECTION: |
METAL CATION IDENTIFICATION |
| PROJECT TITLE: |
ID of IRON (II) and (II) Cations by Precipitation Reactions |
| RELEASE DATE: |
Sunday 21st September 1997 |
| LAST UPDATE: |
Sunday 21st September 1997 |
| VERSION HISTORY: |
1.0, 1.1, 1.2 ( Context updates)
V2.0 ( Text and formatting update - Sep-2009) |
INTRODUCTION:
This is an account on how to detect Iron ions in solution by simple precipitation reactions. Iron is quite easy to distinguish since many of its compounds are insoluble, and have characteristic green (Fe2+) or brown (Fe3+) colour. With The following set of tests it will be easy to confirm Iron without requiring complex procedures or sophisticated equipment.
PRINCIPLE
As mentioned, the tests are simple precipitation reactions. A solution of a Iron salt (Iron Ammonium Sulphate solution for Fe2+ and Iron Chloride for Fe3+.) was mixed with an equal ammount of another solution, which give a physical change, usually a colour change due to a precipitation of the Iron insoluble compound or formation of a complex since Iron is a transitional metal.
Fe++ X (aq) + 2 Na+ Y- (aq) ===> Fe++ 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 Iron, since other metal salts can give the same results. The verification of 4 or 5 such tests will be enough to confirm Iron in an unknown sample.
PROCEDURE
In 10ml testtubes, 4mls of Iron 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. Since Iron can exist in the +2 Oxidation state (Fe2+) as well in the +3 Oxidation state (Fe3+), the reaction were performed in duplicates, one of each for the two different oxidation states
The following compounds was mixed with the Iron salt of which 27 produced a valuable result. These are marked with an Y . In some cases only the Fe3+ produced a reaction and this is marked with a Y.
RESULTS
IRON (II):
a) A DIRTY DARK GREEN precipitate was formed which did not dissolved on xs.
b) No further reaction on heating.
IRON (III):
a) A RUSTY BROWN ppt was formed, insoluble in xs hydroxide
b) No further reaction on heating.
The insoluble hydroxide was precipitated...
IRON (II):
a) Similarly to the NaOH, a DIRTY DARK GREEN ppt was formed which did not dissolved on xs Ammonia
b) No reaction on heating.
IRON (III):
a) Like the Sodium Hydroxide, a RUSTY BROWN ppt was immediately formed.
b) No further reaction on heating.
Iron Hydroxide was precipitated by Ammonia
IRON (II):
a) A GREYISH GREEN/CYAN ppt was immediately formed. (Insoluble in xs)
b) Heat had no effect on the ppt.
IRON (III):
a) A LIGHT BROWN ppt was formed at once (Insoluble in xs)
b) No further reaction on heating.
In both cases, Iron Carbonate was ppted.
IRON (II):
a) No reaction appears with the Fe2+
b)
IRON (III):
a) YELLOW-CLEAR BROWN solution was formed which seems to decolourize rapidly with mixing to a YELLOW solution.
b) On heating the solution turns to a BROWN-YELLOW precipitate.
A strange reaction took place with the Fe3+. It's a good test to distinguish between Fe2+ and Fe3+
IRON (II):
a) A PALE GREYISH GREEN ppt was formed
b) No further reaction on heating.
IRON (III):
a) A BROWN RED solution was developed.
b) On heating an ORANGE BROWN ppt was formed.
Regarding the Fe2+, the sulphite was immediately preipitated, but for the Fe3+ a very similar rection to the Thiosulphate took place. Again a good test to distinguish between Fe2+ and Fe3+
IRON (II):
a) A THICK BLACK (greenish tinge) ppt was formed.
b) No further reactions on heating, or standing out.
IRON (III):
a) A THICK BLACK ppt was formed
b) No further reaction on heating or standing out.
Black Iron Sulphide was ppted at once.
IRON (II):
a) No reaction or colour change
b)
IRON (III):
a) A brown red solution was formed.
b) On heating a YELLOW BROWN ppt was formed in a BROWN solution, propably a solution of Iodine. Some purple vapour of Iodine was given off as well.
Another similar reaction with the Fe3+ only, hence the formation of a brown solution, which its precipitation taking place only after heating. It could be the fact that the solution formed is due to a transitional complex which breaks down on heating ?!
IRON (II):
a) No reaction on adding the Iodate solution
b) On heating a BROWN ORANGE ppt was formed and vapour of Iodine was also visible. On filtering an ORANGE - LIGHT BROWN ppt was left on the filter paper, and a CLEAR YELLOW-BROWN solution was obtained.
IRON (III):
a) A WHITE ppt was formed on adding few drops Iodate, which dissolved on shaking the tube. This kept taking plce until xs Iodate was added and a CREAM WHITE/ORANGE ppt remained.
b) On heating, the colour darkened slightly to CREAM/ORANGE but no particular change took place.
The Iodate could have been precipitated as a CREAM ORANGE/WHITE ppt. by different pathways in both cases
IRON (II):
a) A GREY GREEN ppt was formed.
b) On heating, no solour changes seem to happen.
IRON (III):
a) A gelatinous YELLOW-LIGHT brown ppt was formed.
b) On heating the precipitate intensified to a BROWN ORANGE ppt
The insoluble IRON phosphates (Fe2+, Fe3+) were precipitated out.
IRON (II):
a) Initially a YELLOW ppt was formed, but on adding more borate solution the colour changed to LIGHT GREEN, GREEN and finally DARK GREEN/BLACK GREEN precipitate
b) No further reaction on heating.
IRON (III):
a) ORANGE BROWN solid was precipitated.
b) On heating the ppt intensified slightly to pure BROWN colour
Iron Borate was precipitated. It seems evident that the Fe3+ is the first to be precipitated out since the Fe2+ solution slightly posses Fe3+ and hence this is the reason of the initial yellow ppt formed.
WOW! this could be a very unique test for Fe3+ Ions:
IRON (II):
a) No reaction until few mls of salicylate were added which resulted in a colour change to a PEACH-BROWN solution.
b) On heating the colour decolorized slightly to a CLEAR BROWN yellow solution
IRON (III):
a) On adding few drops, a unique VIOLET solution was formed. On adding few more drops of salicylate, a DARK PURPLE/VIOLET solution (very near to a potassium permangante solution) was developed. On adding xs, this colour changed to a GPURPLE RED, BROWN RED, and finally DARK BROWN (vermouth like) colour. On adding Fe3+ the intially violet colour forms back). It was noted that on the addition of NaOH, the colour changes to a brown yellow due the formation of a ppt (possibly Iron Hydroxide)
b) On heating the violet colour slightly decolorize, but no particular change on the whole.
Very complex reactions taking place here. However the latter is a very unique identification test for Fe3+
IRON (II):
a) No reaction
b) No reaction
IRON (III):
a) CREAM ppt is initially formed which dissolved on shaking. This continued to take place until on adding some mls the ppt did not dissolved any more. In xs benzoate a PEACH/LIGHT BROWN ppt was formed
b) On heating, the ppt turned to BROWN colour
ANOTHER EXCELLENT TEST FOR IDENTIFICATION OF IRON !!!
IRON (II):
a) Initially a CLEAR GREY VIOLET SOLUTION was formed, but on standing after 30-60 seconds, the colour intensified to a DARK RASPBERRY VIOLET SOLUTION.
On standing for further time (15mins) a the colour intensified further to a BLACK colour and a ppt was seen to form. On filtering this mixture, a CLEAR VIOLET SOLUTION + A BLACK PPT was resulted.
b) On heating the initial dark violet solution, a BLACK ppt + a CLEAR VIOLET solution was obtained.
IRON (III):
a) On adding few drops a DARK BLUE solution was immediately formed. On adding xs Tannic acid, the colour changed to a DARK RASPBERRY VIOLET solution. Filtering the dark blue solution resulted in some BLACK DEPOSITS and BLUE SOLUTION. Similarly filtering the violet solution (after left to stand for about 10 mins) produced a VIOLET SOLUTION + some BLACK PPT on the filter paper.
b) On heating, the Blue solution turned to a BLACK ppt (+ colourless solution), but there was no colour change or precipitation on heating the Dark Violet solution (obtained by xs Tannic acid).
Very complex reaction taking place, which involves the transitional chemistry of Iron. The final black precipitate could be that of Iron Tannate. The colour depends on the concentration of the Fe3+ solution. Very weak (i.e Tannic Acid in xs) = violet, then grey-blue, deep Blue, and blue-green (ie Fe3+ in xs).
IRON (II):
a) There was a slight colour change from the clear green/brown solution of the Fe2+ to a clear LIME GREEN solution. No ppt formed though.
b) No change on heating
IRON (III):
a) Similarly there was a slight colour change from the clear brown solution of the Fe3+ to a CLEAR YELLOW solution. No ppt was formed.
b) No change on heating
The reaction involved is like that of converting the contaminating Fe3+ ions in the Fe2+ solution to Fe2+, hence a total green colour and vice versa for the Fe3+ i.e converting any Fe2+ to Fe3+. However this is just an opinion, and nothing chemically proven. The test in feact can be considered as negative.
IRON (II):
a) No reaction
b) On heating strongly, a DIRTY GREEN BLACK ppt was formed (but in very little ammounts. This is considered as a negative result
IRON (III):
a) On adding few mls of the Methanoate, a brown orange solution was formed. After about 1 minute the solution started to turn into an ORANGE-BROWN precipitate.
b) No particular effect on heating apart from increasing the precipitation rate.
Iron (III) methanoate have been precipitated, unlike with Iron (II) which produced no rapid or obvious ppt.
IRON (II):
a) No immediate reaction on adding the ethanoate solution.
b) On heating strongly, a DIRTY GREEN BLACK ppt was formed (but in very little ammounts. This is considered as a negative result
IRON (III):
a) An ORANGE BROWN solution was formed on adding few mls of ethanoate sol. After about 1 minute the solution started to turn into an ORANGE-BROWN precipitate.
b) No change on heating apart from increasing the precipitation rate.
This reaction was SIMILAR not to say identical to the Methanoate test!
IRON (II):
a) The solution turned from yellow/brown to olive green solution
b) No further reaction
IRON (III):
a) Solution turned from orange brown to light yellow solution
b) No further reatcion
Since no ppt is formed, this is considered as a negative test.
IRON (II):
a) A GREY GREEN ppt was formed.
b) No further reaction on heating or standing.
IRON (II):
a) A YELLOW ORANGE ppt was immediately formed
b) No further reaction on heating or standing
Insoluble Iron Silicate was precipitated.
WOW!! THIS IS ANOTHER FORMIDABLE CONFIRMATORY TEST FOR Fe2+ / Fe3+
IRON (II):
a) On adding few drops of Ferro(II)Cyanide, a LIGHT GREEN-BLUE solution was formed. On adding more this turned to a CYAN precipitate, but did not dissolved. Filtering seperated the Cyan precipitate and a colourless solution.
b) On heating the ppt turned more BLUISH, but no particular change was detected.
IRON (II):
a) On adding few drops of Ferro(II)Cyanide a beautiful DEEP BLUE (NAVY BLUE) precipitate was formed. Filtering resulted in this DARK BLUE ppt as the residue, and a COLOURLESS solution as the filtrate. On adding xs Cyanide, the ppt seemed to dissolve and formed a LIGHTER BLUE ppt / BLUE SOLUTION. On filtering this mixture a BLUE ppt and a CLEAR GREEN solution was obtained. On repeating the latter filtration (after adding xs Cyanide) produced the BLUE ppt, but the filtrate was rather COLOURLES/GREEN than the green colour initially obtained; perhaps this is due the diluting of the reagents made to visualize the colours better (otherewise too dark to determine the exact colour)
b) Heating had no effect on the NAVY DEEP BLUE ppt formed.
Excellent reaction for distinguishing Fe2+ and especially Fe3+. The precipitates are propably the insoluble Cyanides of Fe2+ and Fe3+, the latter comprising a transitional complex reaction when it dissolves in xs.
IRON (II):
a) This resulted a similar reaction as that with Ferri(II)Cyanide + Fe3+. A Deep (NAVY) BLUE ppt was imemdiately formed. Unlike the prvious test, on adding xs Ferri(III)Cyanide, the ppt dissolved forming a DEEP BLUE solution. Filtering this in fact gave the blue solution as a filtrate with few deposits on the filter paper.
b) On heating + standing no further reaction took place.
IRON (II):
a) Initially a BROWN SOLUTION was formed without precipitation.
b) Only on heating strongly a DARK OLIVE GREEN PPT was formed. On filtering this, an OLIVE GREEN SOLUTION was obtained, leaving a DARK GREEN/BROWN PPT as residue.
Formation of solid Iron(II) and Iron (III) Ferri(III)Cyanides and complexes
IRON (II):
a) This formed a DARK BLACK BROWN PPT
b) No further reaction on heating, standing or adding xs.
IRON (III):
a) A YOLK YELLOW PPT (Sunsation milkshake!) was formed
b) No further reaction on heating, standing or adding xs.
This is another coloured ppt that Iron formed. Here the precipitation of the Iron Vanadates, have took place.
IRON (II):
a) Brown solution formed which later turns to a SOIL BROWN ppt on standing
b) Heating results of the brown ppt immediately. c) On adding the permanganate dropwise, the following colour changes took place: Yellow (decolirization of the permanganate), brown-yellow, brown, dark brown, red-brown purple-red/brown mixture. This indicates that the colour is masked by the unreacted violet permanganate solution. In fact, filtering confirmed the BROWN ppt and gave the unreacted permanganate solution as the filtrate.
IRON (III):
a) No colour change on adding the permanganate or standing.
b) However on heating strongly, the SOIL BROWN ppt was formed, but in relatively smaller ammounts from the Fe2+. Filtration is required to detect the brown ppt since it will be masked with the unreacted permanganate solution.
Some of the Iron Permanganate was precipitated. Since the Permanganate ion is an oxidizing agent, the brown ppt is of the Fe3+ ions, being oxidized from the Fe2+ state by the permanganate. However, this cannot be totally proven, as when reacting the permanganate directly wth the Fe3+, no immediate precipitate was formed, and only on heating a little brown ppt was given. In fact the Fe3+ reaction can be considered as a slow or partial precipitation of the Fe2+, since more ppt was given off more rapidly.
IRON (II):
a) A LIGHT MUSTARD BROWN ppt was formed after some seconds. Filtration confirms this ppt colour, since there could be still left some unreacted orange dichromate in the mixture.
b) The precipitate was formed faster when heated
IRON (III):
a) No reaction on adding the dichromate, even after standing for a long time
b) Only on heating the MUSTARD BROWN ppt was formed, but in much smaller ammounts. The reaction is a partial reaction of that with Fe2+ since on adding xs Fe3+, heating and filtering the mixture, The orange dichromate (hence unreacted) was still obtained in the filtrate.
Similar reaction as with the permanganate.
IRON (II):
a) Light BROWN ppt was formed
b) On heating it darkened to FAIRLY DARK BROWN (SOIL COLOUR) precipitate
IRON (III):
a) BAIGE (CAFE-LATTE) Precipitate was formed.
b) No particular effect on heating
IRON (II):
a) Initially a CLEAR BROWN SOLUTION was formed and no ppt was given off.
b) On heating the brown solution turned to DARK BROWN, GREYISH, BLUE and on heating further, a BLUE-GREEN solution was formed. No ppt was formed.
IRON (III):
a) A BRIGHT (FLUORSCENT) YELLOW PPT was formed
b) No reaction on heating or adding xs.
Wth Fe2+ a complex reaction involvoing transition chemistry could have taken place. Regards Fe3+, the insoluble Iron(III)Molybdate has been precipitated.
IRON (II):
a) No reaction initially, even upon adding xs BiSelenite
b) On heating strongly some ppt, Peach brown in colour was formed. However this is not a good indicative test since liitle ppt was formed.
IRON (III):
a) With the first few drops a light BROWN/ORANGE PPT was formed but on adding in xs a WHITE YELLOW PPT was formed.
b) No further reaction on heating.
Insoluble, yellow/white Iron(III) Biselenite was precipitated out. Initially masked by the brown Fe3+ solution as a LIGHT BROWN ppt.
IRON (II):
a) No reaction
b) No reaction neither on heating
IRON (III):
a) A unique DEEP BLOOD RED Solution was formed. No ppt after filtering this off. No reaction on xs either.
b) On heating, the colour lost its clearness and became more brownish (thus brownish red.) On filtering, a Light brown ppt was left on the filter paper giving a red-orange solution.
A characteristic test for Fe3+. The red solution is due to the formation of a characteristic complex transitional ion -> [ Fe(SCN) ] 2+
CONCLUSION
IRON (II):
The green / cyan ppt, insoluble in xs formed with the Hydroxide and Carbonate is already a good indication of the presence of Fe2+. However two excellent tests for the confirmation of Fe2+ are those with Tannic Acid (raspberry violet sol), Ferro(III)Cyanide (deep blu sol), Ferro(II)Cyanide (Sky Blu ppt), Sodium Sulphide (black ppt), Potassium Dichromate (Mustard brown ppt), and a varied range of other anions to choose from
IRON (III):
The rusty brown ppt, insoluble in xs formed with the Hydroxide and Carbonate indicates strongly the presence of Fe3+. This can be confirmed with just 3 further test, hence the blood red solution obtained with Potassium Thiocyanate, and the Deep blue sol obtained by Tannic acid, and similar colour with Potassium Ferro(II)cyanide. again there is a good range of colourful ppt to further confirm the Fe3+, such as the Sulphide, Sulphite, Vanadate, Tungstate, etc.
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