CHEMISTRY :
Metal Cation Identification
S T R O N T I U M
PROJECT CODE: |
02.10 |
SECTION: |
METAL CATION IDENTIFICATION |
PROJECT TITLE: |
ID of STRONTIUM Cations by Precipitation Reactions |
RELEASE DATE: |
03 JUNE 1998 |
LAST UPDATE: |
03-June-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 Strontium ions in solution by simple precipitation reactions. Strontium is difficult to distinguish since it forms quite few insoluble and common precipitates. With the following set of tests it will be a guide to confirm Strontium without requiring complex procedures or sophisticated equipment.
PRINCIPLE
As mentioned, the tests are simple precipitation reactions. A solution of a Strontium salt (Strontium 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 Strontium insoluble compound.
Sr++ 2X- (aq) + 2 Na+ Y- (aq) ===> Sr++ 2Y- (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 Strontium, 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 Strontium cations. However the verification of 4 or 5 such tests will be enough to confirm Strontium in an unknown sample.
PROCEDURE
When some Strontium Nitrate was dissolved in water, a slight white precipitate was resulted perhaps due a slight contamination. Filtering this Strontium solution would prepare a clear solution.
In 10ml testtubes, 4mls of this clear Strontium solution was placed. To this, 1 drop of the reagent was initially added, followed by the further addition of about 2mls solution, and finally in xs. The reagents includes the following compounds all having different anions (-ve). If desired, the mixture was heated gently to increase rate of reaction. If a precipitate was formed, an xs volume of the anion (eg Hydroxide) was added to determine wether the ppt is soluble in xs reagent.
The following compounds was mixed with the Strontium salt of which 13 produced a valuable result. These are marked with an Y in the React Column .
RESULTS
a) A very FAINT WHITE ppt was formed, which was insoluble in xs Hydroxide. Can be considered as no reaction.
b) No further change on heating.
A very good identification test since this showed that Strontium have a solable (or slightly insoluble) hydroxide. This characteristical reaction was showed to some extent only by Strontium younger brother, hence Barium!
a) A very FAINT WHITE ppt was formed, which was insoluble in xs Ammonia. Can be considered as no reaction.
b) No further change on heating.
As above; many metals precipitate their hydroxide from Ammonia, but Strontium failed to do this, as so does Barium!
a) A MILKY WHITE ppt was formed.
b) no further reaction on heating on standing.
White Strontium Carbonate was precipitated, lime most other carbonates.
a) A WHITE ppt was immediately formed.
b) No further reaction occured
Strontium Sulphate was precipitated, again like Barium (and others such as Calcium and Lead)
a) A WHITE PPT was given rapidly
b) No further rection on heating or standing.
White and insoluble Strontium Sulphite was precipitated. No gases were detected.
a) A WHITE ppt was formed.
b) No further reaction on heating or xs.
Strontium Sulphide was precipitated as a white solid.
a) No ppt was formed until xs Fluoride was added where a WHITE ppt was formed. Could be a false result!
b) No further reaction.
Not so clear but the Strontium Fluoride could have been precipitated.
a) This gave a WHITE ppt insoluble in xs
b) No further reaction
The Iodate was precipitated
a) A MILKY WHITE ppt was formed
b) No reaction on heating/standing
White Strontium Phosphate precipitation.
a) A WHITE ppt was formed
b) No further reactions
The Borate of Strontium was precipitated as a white solid
a) No reaction on the addition of the Citrate to the Strontium solution.
b) On standing for some minutes after heating, a white ppt was slowly forming.
Could be a slow reaction and the Citrate was precipitated
a) A MILKY WHITE ppt was formed.
b) No effect on heating or standing.
Strontium Silicate was precipitated as a white solid.
a) No reaction on the addition of the Molybdate to the Strontium solution.
b) On standing for some minutes after heating, a white/cream ppt was slowly forming.
White Strontium Molybdate was precipitated.
CONCLUSION
The first indication is the lack of precipitate (or just a faint one) with Sodium Hydroxide and Ammonia.
It is further confirmed by the insoluble Sulphate and Sulphite, which will lead the choice between Barium and Strontium, the only which gives the above results. If calcium fails to produce the hydroxide (very rarely), it will also get in consideration, but Calcium will form a dense White ppt with the Tungstate
Strontium can be distinguished from Barium, because Barium will react with Tannic acid, and more noticably, with Ferro(II) Cyanide, (white) Ferro(III) cyanide (Yellow brown) and Vanadate (Yellow/orange) while Strontium does not.
Finally, Strontium gives a magnificent red flame test, used in red-coloured fire works. Thanks Tony Camilleri for the Strontium Nitrate and have a great firework feast at Luqa!!!
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