CHEMISTRY :
Metal Cation Identification
T I N (II)
| PROJECT CODE: |
02.06 |
| SECTION: |
METAL CATION IDENTIFICATION |
| PROJECT TITLE: |
ID of TIN (II) Cations by Precipitation Reactions |
| RELEASE DATE: |
9 JULY 1997 |
| LAST UPDATE: |
01-Aug-98 |
| 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 Tin ions in solution by simple precipitation reactions. Tin is quite easy to distinguish since many of its compounds are insoluble, however many are white in color, end so it is not so easy to distinguish between other amphoteric metal cations such as Zinc, Aluminium, Lead, etc. With The following set of tests it will be easy to confirm Tin without requiring complex procedures or sophisticated equipment.
PRINCIPLE
As mentioned, the tests are simple precipitation reactions. A solution of a Tin salt (Tin (II) Chloride) was mixed with an equal ammount of another solution, which give a physical change, usually a colour change due to a precipitation of the Tin insoluble compound.
Sn+ X- (aq) + Na+ Y- (aq) ===> Sn+ Y- (s) + Na+ X- (aq)
(s) Solid precipitate forming a colour change in soultion
One type of reaction is not enough, to confirm the presence of Tin, since other metal salts give the same results. For Example with NaOH, many metals give a white ppt., and hence one can't say that the formation of a white ppt of an unknown sample with NaOH is 100% due to Tin cations. However the verification of 4 or 5 such test will be enough to confirm Tin in an unknown sample.
PROCEDURE
In 10ml testtubes, 4mls of Tin 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 formed.
When dissolved in water, my Tin (II) chloride formed a milky solution, which turned to faint yellow if boiled. A colourless solution was needed, since otherwise the whitiness of the solution will interfere with the interpretation of the results. A strong solution of Tin (II) chloride was formed and heated up to about 60 C (otherwise a yellow solution will result on boiling?!) The solution was filtered twice. If the solution remained light milky, it was poured in a tall measuring cylinder and let for a few hours so that the fine deposit will settle at the bottom, and the clear upper solution was carefully transferred to a dry beaker. Sometimes adding of water and heating this solution, will reform the ppt. Very strange indeed!!!
The following compounds was mixed with the Tin salt of which only 24 produced a valuable result. These are marked with an Y in the React Column .
RESULTS
a) A MILKY WHITE PPT was formed
b) On exess the white ppt DISSOLVED forming again a clear solution. c) No reaction on heating
White insoluble Tin Hydroxide was formed. On exess Hydroxide the soluble Sodium Stannate formed, and hence a clear solution was produced. [ Sn(OH)4 ] 2-
a) A MILKY WHITE PPT was formed
b) The white precipitate DID NOT DISSOLVED on adding exess ammonia solution. c) No further reaction on heating
Tin (II) Hydroxide was formed. No complex with ammino ions.
a) A WHITE PPT was formed immediately.
b) No reaction on exess c) No further reaction on heating
Insoluble White Tin Carbonate was formed.
a) A DENSE THICK WHITE ppt was formed.
b) No effect on heating or standing
Tin (II) Sulphite was precipitated. (same reaction with Metabisulphite)
a) A VERY DARK BROWN ppt was formed at once, which dissolves in xs Sulphide to a colourless (Pale Yellow) solution
b) No further reaction on heat or xs sulphide
The Sulphide was precipitated. On xs the colourless [ SnS3 ] 2- complex ion was formed.
a) No reaction with the few drops of iodide, but on adding xs iodide and leaving for a few minutes a FAINT YELLOW WHITE PPT was formed.
b) No colour change on heating.
The iodide is also a white insoluble salt of Tin.
a) With the first drops, a dark brown ppt was obtained. On adding further Iodate, and shaking vigourously the tube, the ppt turned to a dirty green ppt. Adding further Iodate solution, a YELLOW/CREAM WHITE ppt was finally formed which consisted of a WHITE PPT + A YELLOW SOLUTION.
b) No reaction on heating
Very starnge reaction, but finally, Iodine was released together with an insoluble White Iodate of TIN.
a) A CLOUDY WHITE PPT was immediately formed
b) No reaction on heating or exess
Insoluble white Tin Phosphate was formed.
a) An INTENSE MILKY WHITE ppt was immediately formed.
b) Partially soluble in xs benzoate as the intensity was reduced to a faint white colour c) No reaction on heating
A thick white ppt of the extremely insolunle Tin Benzoatewas formed, which seems to be soluble in xs.
a) A MILKY WHITE was formed immediately.
b) No reaction on exess or heating.
White Tin (II) Tannate was formed.
a) A MILKY WHITE ppt was formed immediately
b) No reaction on exess or heating.
Tin(II) Malate, which is a white solid, was formed
a) A MILKY WHITE ppt was formed immediately
b) No reaction on exess or heating.
White solid Tin(II) Methanoate was formed
a) A MILKY WHITE was formed immediately.
b) No reaction on exess or heating.
White Tin (II) Acetate was formed.
a) A MILKY WHITE PPT was immediately formed
b) On xs the white ppt dissolved. c) No further reaction on heating.
Tin forms a complex reaction with citrate.
a) A DENSE THICK WHITE ppt was formed, which dissolved slowly in xs silicate.
b) No effect on heating or standing
Insoluble White Tin(II) Silicate was precipitated, forming a sol complex with xs Silicate.
a) An INTENSE WHITE PPT as formed
b) No reaction on adding xs or heating.
Propably, insoluble white Tin Ferro(II)Cyanide was formed. A different reaction might occurred.
a) A WHITE/LIGHT BLUE (CELEST) PPT was immediately formed
b) No effect on leaving to stand, xs or heating.
a) A GREEN GRAY PPT was formed.
b) On adding xs Vanadate, the ppt darkened up gradually to form a dark green solution (+ some remaining grey green ppt). When dropped on filter paper or tissue paper, this dark green solution seperated into two colours, being an inner green(/blue) colour, and an outer yellow colour. Very unique reaction! c) No further reaction on heating
A complex reaction resulted on the addition of xs vanadate. The dark green solution seems to consist of two soluble compounds, one yellow, and one green/blue in color. The exact color changes from the first drop of vanadate till xs is as follows: Olive green -> blue-green -> grey-green -> dark green -> black green
a) A DARK BROWN PPT was formed. On repeating, a very small ammount of brown ppt was formed, in the unreacted violet permanganate. On adding the permanganate dropwise, the few drops were initially decolourized, then a pink -> dark red -> violet solution was formed on adding more permanganate.
b) Heating seems to speed up the reaction, forming more brown ppt. c) No reaction on xs permangante.
Very starange reaction, mainly baecause the total brown pptand colourless solution I got from the first time I performed the reaction was never achieved again, when repeating the reaction.
a) On adding few drops of dichromate a series of color changes took place as follows: Colourless -> clear sky blue solution -> olive green (perhaps a mixture of the initial blue colour + xs orange dichromate) -> yellow-green -> orange -> formation of RUSTY BROWN PPT. On filtration, the mixture separated into a brown precipitate and an orange solution.
Complex reactions took place propably due the different oxidizing states of chromium.
a) A LEMON YELLOW (FAINT YELLOW) ppt was formed.
b) This ppt did not dissolve on xs tungstate on no reaction on boiling or standing
The formation and precipitation of yellow Tin(II) Tungstate have taken place.
a) The general reaction is the immediate formation of A DARK BLUE/BLACK ppt.
b) Very complex reactions took place on this reaction:
1) Adding dilute (or just 1 drop) of Molybdate: A DIRTY GREEN PPT was formed. On heating slowly, the black green deposited at the base on the tube leaving a brown solution. On further heating, the brown solution also precipitated as a brown solid over the black deposit, leaving a clear solution. On shaking, a DARK BROWN PRECIPITATE was resulted.
2) Adding xs molybdate: A very DARK BLUE-GREEN PPT was formed. When a portion of this was added further xs molybdate, a dark GREEN-BLUE SOLUTION (no PPT) was formed, hence the ppt dissolved in xs to give this black apperaing solution (on dilution with water, the blue-green colour was confirmed.) On standing, the green component is lost making the solution turn to a DARK BLUE colour.
On heating/boiling the dark blue colour looses some of its intensity forming a paler blue-grey colour.
3) Filtering:
a) Filtering a freshly prepared ppt. Residue: BLACK-GREEN solid Filtrate: CLEAR GREEN solution
b) Filtering a freshly prepared pptafter boiling for some seconds Redisue: DARK BLUE / BLACK solid Filtrate: DEEP BLUE solution *
c) Filtering precipitate after 20 minutes standing Residue: DARK BLUE / BLACK solid Filtrate: DEEP BLUE solution *
* Heating the deep blue filtrate made this turn to a PALE BLUE-GREY solution as above in (2)
Very complex reaction(s) taking place. It seems that the initial black green ppt dissolves in xs molybdate (improved by heating or standing) forming a dark intense blue solution (have to be diluted approx 1:20 to give a clear blue solution). This then formed a more clear blue solution on heating.
a) On adding the few drops of selenite, a YELLOW-WHITE (CREAM) ppt was formed which turned to a LIGHT YELLOW-BROWN PPT on heating
b) On adding xs selenite, a white ppt which immediately turned to an ORANGE BROWN PPT (RUBBER ORANGE) was formed.
On heating the orange brown colour intensified. On appearance the RUSTY-BROWN ORANGE colour appears to be due to a ppt, but surprisingly, when filtered the filtrate was still brown orange leaving very few deposits on the filter paper. Hence no ppt was formed, even if the solution was opaque (light did not pass)
a) A FAINT WHITE PPT was formed
b) Slightly intensified to a whiter ppt on heating
Possibly, the thiocyanate of the metal was precipitated slowly.
CONCLUSION
Tin is characterized by the dissolving of the white ppt in xs NaOH forming the stannate soluble ion. Zinc, Lead, and Aluminium, also produces a similar reaction of which Zinc can be eliminated as it forms a soluble complex with xs Ammonia solution as well.
Hence after this first two tests with xs hydroxide and ammonia, the presence of Tin solution has to be distinguished from lead (which gives a yolk yellow ppt with Iodide and Dichromate) and Aluminium, which does not form white ppt with Borate, Tannate, Citrate and FerroCyanide as Tin does. Also the dark brown ppt with the Sulphide, the dark blue/black ppt soluble in xs with the Molybdate and the orange opaque solution with the Biselenite are unique test for Tin, which on the contrary Zn and Al forms white ppts.
Further confirmatory and unusual reactions for tin are those with the Vanadate and to a less extent with the Dichromate. It seems that particular reactions took place with the transition anions salts (dichromate, vanadate, permanganate). Also, very few metal salts form white ppt with the > Malate < Citrate (which dissolves in xs ) Ethanoate and Methanoate.
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