Metal Cation Identification
C A L C I U M
| PROJECT CODE:
|| METAL CATION IDENTIFICATION
| PROJECT TITLE:
||ID of CALCIUM Cations by Precipitation Reactions
| RELEASE DATE:
|| 06th NOVEMBER 1997
| LAST UPDATE:
| VERSION HISTORY:
|| 1.0, 1.1, 1.2 ( Context updates)
V2.0 (Text and formatting update - Sep-2009)
This is an account on how to detect aluminum ions in solution by simple precipitation reactions. Aluminium is not very easy to distinguish since most of its compounds are soluble, and those which are not are white. With the following set of tests it will be easy to confirm Aluminium without requiring complex procedures or sophisticated equipment.
As mentioned, the tests are simple precipitation reactions. A solution of an Aluminium salt (Aluminium Sulphate) was mixed with an equal ammount of another solution, which give a physical change, usually a colour change due to a precipitation of the Calcium insoluble compound.
Ca++ 2X- (aq) + 2 Na+ Y- (aq) ===> Ca++ 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 aluminium, 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 Aluminium cations. However the verification of 4 or 5 such test will be enough to confirm Aluminium in an unknown sample.
In 10ml testtubes, 4mls of Aluminium 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 was mixed with the aluminium salt of which only 16 produced a valuable result. These are marked with an Y in the React Column .
01 * Sodium Hydroxide
02 * Ammonium Hydroxide
03 * Sodium Carbonate
04 * Potassium Sulphate
05 Sodium ThioSulphate
06 * Sodium (Metabi)Sulphite
07 * Sodium Sulphide
08 * Sodium Fluoride
09 Sodium Chloride
10 Potassium Bromide
11 Ammomium Iodide
12 * Potassium Iodate
13 * Ammonium Phosphate
14 * Sodium TetraBorate (Borate)
15 Sodium Salicylate
16 Sodium Benzoate
17 Tannic Acid
18 Sodium Malate sol.
19 Sodium Methanoate sol.
20 Sodium Ethanoate
21 * Sodium Citrate
22 Sodium Tartarate
23 * Sodium Silicate
24 * Potassium Ferro(II)Cyanide
25 Potassium Ferri(III)Cyanide
26 Sodium Vanadate
27 Potassium Permanganate
28 Potassium Dichromate
29 * Sodium Tungstate
30 * Ammonium Molybdate
31 Sodium BiSelenite
32 Potassium Thiocyanate
a) This gave a MILKY WHITE PPT. insoluble in exess Hydroxide
b) No reaction on heating
Unslouble (slightly soluble) white Calcium Hydroxide was formed.
a) This gave no immediate ppt.
b) On heating and standing for some hours, few cloudy white ppt was formed.
Ammonia is unable to precipitate the sparingly soluble Calcium Hydroxide
a) A WHITE PPT was immediately formed
b) No reaction on heating or exess
Insoluble white Calcium Carbonate was immediately formed.
a) A white precipitate was formed slowly.
b) Heating the mixture, made faster the reaction, and the white precipitate
was quickly formed.
Calcium Sulphate is an insoluble white substance.
a) No reation when mixture is room temp.
b) On boiling, the reaction formed a white ppt, and the liquid bumped violently
on reaching the boiling point.
Propably the white compound is Sodium sulphite, and it's reaction rate is slower
from the sulphate one. Also it is possible that heating have in some way
converted the Sulphite into Sulphate, and the ppt formed was due the sulphate.
a) After letting to stand for few minutes, the clear solution turns slightly
dirty due the formation of a very faint white ppt.
b) On heating a light grey, faint white ppt was formed and fell to tha bottom
of the tube.
Slow formation of the insoluble light grey Calcium Sulphide took place. Heating
increased the rate of reaction.
a) A faint white ppt was formed, which did not intensified on standing.
b) No further reaction on heating.
An exact similar ppt took place with the Al and Mg solutions.
a) No immediate precipitate or colour change.
c) A WHITE PPT was formed only after standing for some quite time or heating.
Precipitation of the insoluble Calcium iodate. Don't know why this was not
spontanous (i.e formed as soon as the two solutions were mixed.)
a) A WHITE PPT formed at once.
b) No further reaction on heating.
Calcium also bears an insoluble phosphate.
a) A dense WHITE PPT. was formed rapidly.
b) No further reaction on heating
White insoluble Calcium Borate was formed.
a) No reaction at all
b) On heating a WHITE precipitate was formed.
This is an interesting test, since Citrate does not form a ppt in any way with
Mg and Al. An excellent test to distinguish between Mg and Ca for example. White insoluble Calcium Borate was formed.
a) WHITE ppt was formed rapidly.
b) No reaction on heating or standing.
White Calcium Silicate was formed.
a) No reaction or ppt detected
b) On heating a little white fine ppt was formed.
Don't know if its an experimental error, but I would not rely on and perform
a) A MILKY WHITE ppt was formed rapidly.
b) No further reaction, due to heating, xs tungstste or standing
a) No initial precipitation or reaction
b) On heating, a FAINT WHITE PPt was formed.
From the results aboove, Calcium can be easily traced. The first test is the
formation of a white precipitate with Sodium Hydroxide (undissolved in exess)
and the lack of a ppt with Ammonium Hydroxide. Next comes the sulphate test,
which eliminates most transition metals, Al and Mg.
The citrate ppt will confirm the presence of calcium. Of course further tests such as the borate and
metabisulphite can be performed for further confirmation if desired. The
Phosphate, Iodate, Fluoride and Carbonate are of no help.
Metal Cation ID Section Links
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