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CHEMISTRY : Metal Cation Identification


PROJECT TITLE: ID of BARIUM Cations by Precipitation Reactions
LAST UPDATE: 02 May 1998
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 Barium ions in solution by simple precipitation reactions. Barium is quite easy to detect since it has many insoluble compounds, although most of them are white. With the following set of tests it will be easy to confirm Barium without requiring complex procedures or sophisticated equipment.


As mentioned, the tests are simple precipitation reactions. A solution of a Barium salt (Barium 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 Barium insoluble compound.

Ba++ 2X- (aq) + 2Na+ 2Y- (aq) ===> Ba++ 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 Barium, 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 Barium cations. However the verification of 4 or 5 such test will be enough to confirm Barium in an unknown sample.


In 10ml testtubes, 4mls of Barium salt 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 were mixed with the Barium salt of which 17 produced a valuable result. These are marked with an Y in the React Column .
01 Sodium Hydroxide
02 Ammonium Hydroxide
03 Sodium Carbonate Y
04 Potassium Sulphate Y
05 Sodium ThioSulphate
06 Sodium (Metabi)Sulphite Y
07 Sodium Sulphide Y
08 Sodium Fluoride Y
09 Sodium Chloride
10 Potassium Bromide
11 Ammomium Iodide
12 Potassium Iodate Y
13 Ammonium Phosphate Y
14 Sodium TetraBorate (Borate) Y
15 Sodium Salicylate
16 Sodium Benzoate
17 Tannic Acid
18 Sodium Malate sol.
19 Sodium Methanoate sol.
20 Sodium Ethanoate
21 Sodium Citrate Y
22 Sodium Tartarate
23 Sodium Silicate Y
24 Potassium Ferro(II)Cyanide
25 Potassium Ferri(III)Cyanide
26 Sodium Vanadate Y
27 Potassium Permanganate
28 Potassium Dichromate Y
29 Sodium Tungstate Y
30 Ammonium Molybdate Y
31 Sodium BiSelenite
32 Potassium Thiocyanate


01: Sodium Hydroxide

a) This gave no immediate ppt.

b) After leaving for about 10 mins, a faint white ppt formed slowly, which apparently dissolved on heating. This test is regarded as no ppt was formed

Barium has a soluble (slightly unsoluble Hydroxide) and it is very hard to form a precipitate with NaOH.

02: Ammonium Hydroxide

a) This also gave no immediate ppt.

b) No reaction on heting, and trace ammounts of ppt formed slowly after 20mins or so. This test is regarded as no ppt was formed. Ammonia is unable to precipitate the slightly unsoluble Barium Hydroxide.

03: Sodium Carbonate

a) A MILKY WHITE PPT was immediately formed

b) No reaction on heating or exess

Insoluble white Barium Carbonate was immediately formed.

04: Potassium Sulphate

a) A WHITE PRECIPITATE was formed at once.

b) No further reaction on heating. Barium Sulphate is an very unsoluble white substance, and is the official test for the Sulphate anion.

05: SodiumThioSulphate

a) No reaction takes place

b) On heating and leving for about 20mins, some traces of white ppt formed slowly. Since very low ammount of ppt was formed after heating and long time, this result is regarded as negative. Perhaps some few thiosulphate ions yielded the sulphate ions on heating, which gave the white ppt.

06: Sodium Sulphite (or Sodium Metabisulphite)

a) Similar to the sulphate, a WHITE PPT was formed rapidly.

b) No further reaction on boiling

Precipitation of the insoluble Barium Sulphite.

07: Sodium Sulphide

a) A WHITE ppt was formed on adding the Sulphide to the Barium sol.

b) No further reaction on heating or adding xs Sulphide

Precipitation of white Barium Sulphide.

08: Sodium Fluoride

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 Ca, Al and Mg solutions. The flouride of metals seem to be all unsoluble.

09: Potassium Iodate

a) A MILKY WHITE PPT was formed exhibiting the "Titanic" effect.

b) No effect on heating or standing. White and heavy (dense) Barium Iodate was precipitated

10: Ammonium Phosphate

a) A dense WHITE PPT formed at once. As other phosphates, this ppt sinks rapidly to the base of the testtube.

b) No further reaction on heating. Barium also bears an insoluble phosphate.

11: Sodium TetraBorate

a) A WHITE PPT. was formed rapidly.

b) No further reaction on heating

White insoluble Barium Borate was formed.

12: Sodium Citrate

a) A dense white ppt was immediately formed.

b) On heating, no other reaction took place. Barium Citrate, like Calcium, is a white insoluble compound.

13: Sodium Silicate

a) A WHITE ppt was formed

b) No further reaction on heating or standing. Solid white Barium Silicate was formed

14: Sodium Vanadate

a) This gave a CREAM / PALE YELLOW PPT and a pale yellow/colourless solution.

b) No further reaction on heating apart from perhaps speeding up the reaction

Barium Vanadate is formed, also with the posible formation of a vanadium soluble salt which is colourless / pale yellow in colour.

15: Potassium Dichromate

a) The apparent precipitation is of an orange precipitate, however filtration had shown that the reaction formed a DENSE HIGH-LIGHTER YELLOW PPT at the bottom of the tube, leaving an orange solution, propably a chromium salt.

b) No further reaction on heating. The complex dichromate ion broke to give chromate and chrome salts. Barium Chromate is a bright yellow compound, whereas the chrome ions were orange. Adding more barium salt to the orange filtrate didn't gave off again a ppt.

16: Sodium Tungstate

a) A MILKY WHITE ppt was formed at once

b) No further reaction on heating, standing or adding xs Tungstate

Barium Tungstate was precipitated as a white solid.

17: Ammonium Molybdate

a) A MILKY WHITE ppt was formed

b) No further reaction on heat or standing

The insoluble barium molybdate was formed.


From the results aboove, Barium can be easily traced. The first unique test is the yellow ppt. formed with the DICHROMATE, and the pale yellow ppt with the VANADATE.

An interesting negative test is the lack of precipitation with Sodium Hydroxide and Ammonia. This will also eliminate many metal anions, except of course the Group I metals, and to some extent Calcium , since this hydroxide is sparingly soluble.

Finally, one can confirm Barium with the SULPHATE, CITRATE and BORATE tests, all giving a white ppt at once. However note that these 3 give the same results with Calcium

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