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CHEMISTRY : Metal Cation Identification


PROJECT TITLE: ID of LEAD Cations by Precipitation Reactions
LAST UPDATE: 31-Jul-98
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 lead ions in solution by simple precipitation reactions. lead 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 lead without requiring complex procedures or sophisticated equipment.


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

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


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


01: Sodium Hydroxide

a) This gave a MILKY WHITE PPT.

b) The ppt dissolved in excess Hydroxide forming a clear solution

Insoluble white Lead Hydroxide was formed which in exess NaOH, the Plumbate soluble anion was formed. [ Pb(OH)4 ] 2-

02: Ammonium Hydroxide

a) This gave a DENSE WHITE PPT. insoluble in exess Ammonia

b) No reaction on heating. Insoluble white lead Hydroxide was formed

03: Sodium Carbonate

a) A WHITE PPT was immediately formed

b) No reaction on heating or exess

Insoluble white lead Carbonate was formed.

04: Potassium Sulphate

a) A WHITE PPT was immediately formed

b) No reaction on heating or exess

Insoluble white lead Sulphate was formed.

05: Sodium ThioSulphate

a) A WHITE ppt was formed. Smell of bad eggs was given off (H2.S)

b) On adding xs Thiosulphate, the white ppt turned to a clear solution, which on standing for 1 day, a few grey-black powder was deposited. c) No further reaction on heating. Insoluble Lead Thiosulphate was propably produced, which dissolved in xs forming a Lead complex. The grey powder could be deposit of Lead?!

06: Sodium Sulphite (or Sodium Metabisulphite)

a) A WHITE PPT was rapidly formed.

b) No further reaction on heating. Insoluble Lead Sulphite was produced. If using Sodium Metabisulphite, heating is required to obtain the white precipitate.

07: Sodium Sulphide

a) An INTENSE 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 Lead Sulphide was precipitated. This is one of the main tests for the presence of Lead used in Labs.

08: Sodium Fluoride

a) A DENSE WHITE ppt which was insoluble on heating or xs. Lead Fluoride, insoluble in both cold and hot water was formed.

09: Sodium Chloride

a) A WHITE ppt was formed which dissolved on heating. Lead Chloride was produced which is insoluble in cold but more soluble in hot water

10: Potassium Bromide

a) Same as the chloride, hence a white ppt was formed, which dissolved to a less extent in hot water. Lead Bromide was produced which is insoluble in cold, but more soluble in hot water.

11: Ammonium Iodide

a) An intense YOLK-YELLOW precipitate was formed.

b) No further reaction on heating or xs Lead salt. Precipitation of the Yelloe Lead Iodide.

12: Potassium Iodate

a) A THICK MILK WHITE ppt which sank to the bottom after 10sec (Titanic effect) c) No reaction on heating or standing. The reaction involves the formation of the insoluble Lead Ioadate, which varies in colour from the canary yellow Iodide ppt.

13: Ammonium Phosphate

a) A DENSE WHITE ppt. was immediately formed

b) Ppt. was insoluble in xs Phosphate, and did not react on heating

Insoluble white Lead Phosphate was produced.

14: Sodium TetraBorate

a) A DENSE WHITE ppt. was immediately formed

b) Ppt. was insoluble in xs and did not react on heating

Insoluble white Lead Borate was produced.

15: Tannic Acid

a) No fast precipitation occured but on standing for some minutes the clear faint yellow solution started to darken and become 'dirty'

b) On heating a cloudy LIGHT-GREY/BROWN ppt was formed at the very bottom of the tube. Perhaps the formation of Lead Tannate, but the reaction was not so clear.

16: Sodium Malate solution

a) A WHITE ppt was formed slowly.

b) On heating the ppt dissolved, and some reformed on cooling. c) On addition of very xs (about x 20 as much volume) of Sodium Malate sol. the ppt dissolved. The large volume of malate required could be due using a weak solution of Sodium Malate.

17: Sodium Citrate

a) A milky white ppt was formed.

b) On adding exess citrate, the ppt dissolved to a colourless solution.

18: Sodium Silicate

a) A MILKY WHITE ppt was formed which dissolved in xs Silicate.

b) No further reaction on heating

Insoluble Lead Silicate was formed.

19: Potassium Ferro(II)Cyanide

a) A DENSE WHITE ppt was formed.

b) No further reaction on heating or xs cyanide. An insoluble complex of Lead was propably formed. Also the reaction could be simpler and the ppt is just Lead FerroCyanide.

20: Sodium Vanadate

a) A BROWN-YELLOW ppt was formed.

b) No further on heating or standing

Lead Vanadate was formed which is yellow and insoluble.

21: Potassium Permanganate

Procedure: 2 crystals of the permanganate were dropped in a medium size test-tube, 4/5 full of water. When dissolved, half the solution is placed in another similar test-tubes which serves as a control and to compare the result. To one of the solutions add 1 to 2 drops of lead nitrate solution. N.B. If using a stronger permanganate solution, the experiment could not be appreciated, since of its intense violet colour.

a) The clear violet solution darkens up (but remains violet), and the inside surface of the test tube will get a black tinge. On filtering, some black solid remains on the filter paper.

22: Potassium Dichromate

a) A Yolk-yellow ppt, very similar to the iodide, was formed. Usually, the ppt looks orange due to the orange solution of the dichromate still un-reacted, but on filtering off the ppt is intense yolk-yellow.

b) No reaction on heating or standing

23: Sodium Tungstate:

a) A THICK WHITE ppt was formed immediately

b) No further reaction on heating or adding xs Tungstate.

24: Ammonium Molybdate

a) A MILKY DENSE WHITE ppt was formed at once.

b) No further reaction on heat or standing

25: Sodium Biselenite

a) a THICK WHITE ppt. was immediately formed

b) Ppt was insoluble in xs an no reaction on heating

Insoluble Lead (bi)Selenite was formed.

26: Potassium Thiocyanate

a) No rapid reaction, but on standing a white deposit was forming, especially on the sides of the tube. On closer inspection, the white deposit was actually needle shaped crystals (shiny against light) forming particularly at the edges and some will fall at the base of the tube.

b) Surprisingly enough, on heating, the crystals seams not to disslove, and rather more crystals were formed on heating. No 'true' ppt was formed. Very strange reaction especially that the crystals did not dissolve in hot water.



A solution of Lead Nirate was prepared in a beaker or flask. Fairly concentrated NaOH was added slowly, forming an intense white ppt of Lead Hydroxide. The solution was heated up to 60 C to ensure complete reaction. Heating to boiling would lead to a faint yellow ppt which could be due the formation of Lead oxide from the hydroxide due to heat.

More NaOH was dropped slowly until the intense whites starts to fade to a clear solution. When a faint white ppt solution was achieved, no more NaOH was added. If excess NaOH was added, a clear transperent solution is formed which is a mixture of plumbate + Hydroxide. The Hydroxide would interefere with the tests, so it must be sure that the solution contains no NaOH. So if a clear solution is obtained, few drops of Nitric acid were added until a faint white precipitate was obtained again. The mixture of white solid Lead Hydroxide and soluble Sodium Plumbate was filterd and the filtrate (thus the Plumbate) was gathered.

although I did all the best to produce the free plumbate solution, I am not convinced that I managed to get such a pure sample, but I believe there was some un reacted NaOH as well. The solution had a slimy feel (characteristic of Sodium NaOH), and decissevely alkaline to litmus paper. Hence the following tests for the plumbate could be not valid due to contamination of the hydroxide ions.

Test for Plumbate ions:

About 4mls of the following solutions was prepared and added 2mls - 4mls Sodium Plumbate solution to each.
01 Iron (III) Sulphate: Rusty Brown ppt. Rusty Brown ppt.
02 Zinc Chloride: Thick White ppt. Thick White ppt.
03 Copper Sulphate: Blue sky ppt. Blue sky ppt.
04 Manganous Sulphate: White/cream ppt. Cream ppt.
05 Cobalt Chloride: Navy Blue ppt. Grey/brown ppt.
06 Potassium Chromic Sulphate: Blue/green ppt. Blue/green ppt.
07 Ammonium Nickel Sulphate: Lime green ppt. Lime green ppt.
08 Tin (II) Chloride: Dense White ppt. Dense White ppt.
These colurs have same characteristics as precipitation with Hydroxide solution, but few of the above can clearly show that the colour change was responsible due to the reaction with the Plumbate ions not the Hydroxide, (or just he hydroxide). The precipitation of the Plumbate and hydroxide of the corresponding cations is compared below.


Heating the blue ppt formed by Aluminate or Hydroxide.

Aluminate: No colour change results. Hydroxide: The blue ppt turns black - Hydroxide oxidised to black Copper Oxide


Heating the lilac ppt formed by Aluminate or Hydroxide < - Aluminate: The prissian blue ppt turns to a grey brown ppt on heating Hydroxide: The lilac ppt turns blue - Hydroxide oxidised to blue cobalt Oxide


Add NaOH or Aluminate in exess < - Aluminate: Blue ppt remains on exess; no reaction takes place Hydroxide: Blue ppt turns to a dark green solution due to a complex chrome ion.


The first indications of Lead is the formation of a white ppt with NaOH, dissolving in xs, and the formation of white ppt with Ammonia sol., insoluble in xs. but this has the same charactersitic of other metals such as Aluminium, and Tin.

Further confirmatory tests is the yolk-yellow ppt with the Dichromate and Iodide solutions, and if you prefer also with the Vanadate (N.B. The Vanadate only is not enough since it also gives a yellow ppt with Aluminium). The coal black ppt. with Sodium Sulphide completes the confirmation.

Lead then has many unique reactions, such as with the Citrate, and Thiosulphate, which forms a white ppt, soluble in xs, and the insoluble Sulphate and Chloride, which unlike Barium and Calcium, have soluble chlorides.

The formation of the plumbate, and further tests on the plumbate are not advisable since they yield nearly the same colour changes as with hydroxides. Also it takes a lot of time to prepare the plumbate, and difficult to get the aqueous plumbate ions free from Hydroxide ions.

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