CHEMISTRY :
Metal Cation Identification
S I L V E R
| PROJECT CODE: |
02.19 |
| SECTION: |
METAL CATION IDENTIFICATION |
| PROJECT TITLE: |
ID of SILVER Cations by Precipitation Reactions |
| RELEASE DATE: |
21 JULY 1998 |
| 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 Silver ions in solution by simple precipitation reactions. Silver is very easy to distinguish since most of its compounds are insoluble compounds, however many are white. With the following set of tests it will be easy to confirm Silver, which is one of the transitional metals, without requiring complex procedures or sophisticated equipment.
PRINCIPLE
As mentioned, the tests are simple precipitation reactions. A solution of a Silver salt (Silver Nitrate) was mixed with an equal ammount of another solution, which give a physical change, usually a colour change due to a precipitation of the Silver insoluble compound.
Ag+ 2X- (aq) + 2Na+ 2Y- (aq) ===> Ag+ 2Y- (s) + 2Na+ 2X- (aq)
(s) Solid precipitate forming a colour change in soultion
One type of reaction is not enough, to confirm the presence of Silver, since other metal salts may 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 Silver cations. However the verification of 4 or 5 such test will be enough to confirm Silver in an unknown sample.
PROCEDURE
In 10ml testtubes, 4mls of Silver solution was placed. If using tap water, a white ppt will form, since of the chloride/chlorine present in it. A clear silver Nitrate solution is achieved by filtering this solution, from the solid Silver Chloride formed.
About 2mls of reagent solution of the following compounds all having different anions (-ve) was added. Again if not distilled water is used to dissolve these, chlorine/chloride must be removed from tap water. This is done by adding few drops of silver nitrate in xs tap water. The water is filtered from the silver chloride formed to obtaine a chloride/chlorine free water (perhaps with some xs Silver Nitrate, which will not intefere with the test. The white solution to be filtered had to be boiled and filtered for 3 to 4 times using 542 filter paper before a clear solution was obtained. This slight white ppt formed was strangely enough not blocked by the filter papaer! filtered
When the reagent is added to the silver nitrate solution, any precipitation or colour changes are noted. If desired, the mixture was heated gently to increase rate of reaction, or added in xs perhaps the ppt formed will dissolve (especially for Ammonia and sodium hydroxide.)
The following compounds was mixed with the Silver salt of which 28 produced a valuable result. These are marked with an Y in the React Column .
RESULTS
a) This gave a BROWN ppt which on adding xs, it intensified to a DARK BROWN ppt. This did not dissolve on xs hydroxide.
b) No particular reaction on heating
Insoluble brown Silver Hydroxide was formed.
a) This also gave a BROWN PPT, which dissolved on adding little xs ammonia to a COLOURLESS Solution
b) No reaction on heating.
Insoluble brown Silver Hydroxide was formed, which forms a complex transitional ion on xs. [ Ag(NH3)2 ] +
a) A WHITE PPT which turns to BAIGE on standing was formed.
b) On heating, the precipitate turned to a dark grey colour.
Insoluble white Silver Carbonate was formed. On heating the carbonate decomposed to the black Silver Oxide.
a) A WHITE ppt was formed, but after about 8 sconds the colour turned to BAIGE, then YELLOW, BROWN, and DARK BROWN c) Heating turned thh ppt slightly darker, nearly BLACK.
Insoluble Silver Thiosulphate was propably produced.
a) A WHITE PPT was rapidly formed, which did dissolve in xs into a COLOURLESS solution.
b) When heated, A greyish silvery ppt was formed, whichalso deposited on the interior of the tube wall, forming a greyish coat.
Insoluble Silver Sulphite was produced, which forms a soluble transitional complex on xs sulphite. Could the ppt formed after heating be silver deposits?
a) An INTENSE DARK BROWN/BLACK ppt was formed on the addition of few drops of sulphide
b) No reaction on adding xs Sulphide or boiling (apart from the bad smell!)
The characteristic BLACK Silver Sulphide was precipitated.
a) No reaction.
b) On standing for a long time or heating some DARK GREY/BLACK ppt was formed.
This is an excellent test, although not very clear, both for Silver, and for fluoride, since there is no other metal which posses a black insoluble fluoride.
a) A WHITE ppt was formed which sank to the bottom of the tube after shaking for few seconds.
b) No reaction on heating
Silver Chloride was produced. (An excellent test for the chloride anion)
a) A CREAM / PALE YELLOW ppt was formed. Again sank to the bottom at once. Dissolves on adding very xs bromide to a colourless sol.
b) No further reaction on heating
Silver Bromide was produced, forming a soluble complex on adding very xs [AgBr2]-
a) A LIGHT YELLOWW precipitate was formed. On adding quite xs Iodide the ppt. dissolves to a colourless sol.
b) No further reaction on heating, standing or xs Iodide.
Precipitation of the Yellow Silver Iodide which dissolves in xs iodide to a colourless complex : [ AgI2 ] -
a) A THICK MILK WHITE ppt which sank to the bottom after few sec
b) No reaction on heating or standing.
The reaction involves the formation of the insoluble Silver Ioadate, which varies in colour from the yellow Iodide ppt. A good test to distinguish between Iodate and Iodide!
a) A PALE YELLOW PPT was formed, which darkened on adding xs Phosphate to a YELLOW/LIGHT BROWN ppt.
b) Strangly, on heating the ppt colour turned back to the initial yellow colour
Insoluble white Silver Phosphate was produced.
a) A DENSE MILKY WHITE ppt. was immediately formed
b) On heating, the colour turned to BROWN, then GREY/DARK BROWN ppt.
Insoluble white Silver Borate was produced. Oxidation, or decomposition on heating might have took place.
a) A MILKY WHITE ppt was formed at once.
b) No further reaction.
Insoluble Silver Saliyclate was precipitated.
a) THICK SOLID MILKY WHITE PPT was formed.
b) No effect on heting, but on standing for long time, the white ppt turned into a LIGHT LILAC COLOUR.
Insoluble Silver Benzoate was precipitated. Oxidation on standing may have turned the ppt to lilac, or this was a contaminant.
a) No reaction initially.
b) On heating a GREY/DARK BROWN precipitate and an ORANGE BROWN solution was formed.
Perhaps the formation of Silver Tannate, but the reaction was not so clear.
a) A Brown ppt was formed which darkened slowly on standing.
b) On heating a black ppt was formed, which also covered the inside of the tube. c) After letting to cool and so standing for some minutes, the solution mixture was poured into a clean tube, it was found the the ppt was now GREy/BAIGE in colour
Strange reaction(s) taking place, but the insoluble Silver Methanoate was undoubtly pecipitated.
a) A MILKY WHITE ppt was formed.
b) On adding very exess citrate, the ppt dissolved to a COLOURLESS solution.
THe insoluble Silver Citrate was precipitate which formed a solule complex ion.
a) A WHITE PPT was formed
b) No further reaction on standing, adding xs or heating
Possibly, Silver Tartarate was precipitated. One of the few precipitates obtained with the tartarate anion.
a) An INTENSE LIGHT BROWN ppt was formed.
b) No further reaction on heating
Insoluble Silver Silicate was formed.
a) A DENSE WHITE ppt was formed.
b) On heating, the white ppt turned to PALE BLUE, and the solution turned to CLEAR YELLOW.
An insoluble complex of Silver was propably formed. Also the reaction could be simpler and the ppt is just Silver FerroCyanide.
a) ORANGE BROWN ppt and a yellow solution was obtained
b) No reaction on heating.
The insoluble Silver Ferro(III)Cyanide is an ORANGE/BROWN ppt, and the yellow solution is propably unreacted Potassium Ferro(III)Cyanide (hence in xs).
a) A YOLK YELLOW/ORANGE ppt was formed.
b) No further on heating or standing
Silver Vanadate was formed which is yellow and insoluble.
a) A DARK RED BROWN ppt was formed at once.
b) No reaction on heating or standing
Silver Dichromate was formed
a) A THICK CREAM/WHITE ppt was formed immediately b On heating, the ppt turned to a WHITE ppt.
Another straight forward precipitation, this time Silver Tungstate.
a) A MILKY DENSE WHITE ppt was formed at once.
b) No further reaction on heat, apart that from turning slightly PALE YELLOW in colour
Another straight forward precipitation, this time Silver Molybdate
a) a THICK WHITE ppt. was immediately formed
b) Ppt was insoluble in xs an no reaction on heating
Insoluble Silver (bi)Selenite was formed.
a) a THICK WHITE ppt. was immediately formed
b) Ppt was insoluble in xs an no reaction on heating
Insoluble Silver Thiocyanate was formed.
CONCLUSION
The first indications of Silver is the formation of a DARK BROWN ppt with NaOH, and Ammoinia solution, in which the latter, the ppt dissolved in xs. Also, a very good test is the formation of GREY/BLACK ppt with the Fluoride, since no other metal precipitates a black fluoride deposit.
Further confirmatory tests is the WHITE, CREAM/PALE YELLOW, and YELLOW ppt, insoluble on heating, with Chloride, Bromide and Iodide respectively. The BLACK BROWN Sulphide, is common with many metals, but the DARK RED BROWN ppt with the Dichromate, the LIGHT BROWNW ppt with the Silicate, and the Intentse DARK YELLOW/ORANGE ppt with the Vanadate are unique coloured ppts formed with silver.
Silver then has many unique MILKY WHITE precipitates, such as with the Citrate, Tartarate, Benzoate, Salicylate, Thiocyanate, Iodate, Selenite, etc, but one must bear in mind that Lead also produce many MILKY WHITE, ppt, some of which
Finally, the Ferro(II) and Ferro(III) cyanide does also produce some interesting reactions. Silver is the most metal who had produced insoluble precipitates (28 out of 32 used, so it is quite easy to confirm it's presence in solution.
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