Precipitation of Group 4-Cations• The Group IV cations are Ba2+, Sr2+, Ca2+.• These metals form chlorides, sulfides and hydroxides that are soluble under that prevail in the precipitations of Group I, II, and III.
• The carbonates of barium, strontium, and calcium precipitate in aqueous ammonia solutions containing ammonium carbonate.• These conditions give a carbonate concentration high enough to precipitate BaCO3, SrCO3, and CaCO3 but not MgCO3.
• To bring the solution to the required ammonium concentration, the centrifugate from Group III separation, which contains ammonium salts, is first evaporated to dryness and then heated strongly to expel the ammonium salts present. The equations are: NH4Cl NH3(g) + HCl(g) NH4NO3 N2O(g) + 2H2O(g)
• The necessary ammonium ion concentration is then obtained by adding the group IV precipitant, which consists of ammonium chloride and aqueous ammonia in the required concentrations. Ba2+ + CO32 BaCO3 (white) Sr2+ + CO32 SrCO3 (white) Ca2+ + CO32 CaCO3 (white)
SEPARATION and IDENTIFICATION of BARIUM 1. Dissolution of the CarbonatesBaCO3 + 2CH3CO2H Ba2+ + 2CH3CO2 + H2O + CO2SrCO3 + 2CH3CO2H Sr2+ + 2CH3CO2 + H2O + CO2CaCO3 + 2CH3CO2H Ca2+ + 2CH3CO2 + H2O + CO2 2. Separation of Barium from Strontium and Calcium Cr2O72 + H2O 2CrO4 + 2H+
4. Dissolution of Barium Chromate - A solution of 12M HCl is used to bringabout the dissolution of BaCrO45. Identification of Barium - the presence of barium ion in the solutionis confirmed by precipitating it as bariumsulfate, using sulfuric acid as the precipitant. - flame test- yellow green color
Sodium Hydroxidea) 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 formedBarium has a soluble (slightly unsoluble Hydroxide) and it is very hard to form a precipitate with NaOH.Ammonium Hydroxidea) 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.Sodium Carbonatea) A MILKY WHITE PPT was immediately formedb) No reaction on heating or exessInsoluble white Barium Carbonate was immediately formed.Potassium Sulphatea) 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.SodiumThioSulphatea) 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.Sodium Sulphite(or Sodium Metabisulphite)a) Similar to the sulphate, a WHITE PPT was formed rapidly.b) No further reaction on boilingPrecipitation of the insoluble Barium Sulphite.Sodium Sulphidea) A WHITE ppt was formed on adding the Sulphide to the Barium sol.b) No further reaction on heating or adding SulphidePrecipitation of white Barium Sulphide.Sodium Fluoridea) 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.
Potassium Iodatea) A MILKY WHITE PPT was formed exhibiting the "Titanic" effect. b) No effect on heating or standing. White and heavy (dense) Barium Iodate was precipitatedAmmonium Phosphatea) 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.Sodium Tetraboratea) A WHITE PPT. was formed rapidly.b) No further reaction on heatingWhite insoluble Barium Borate was formed.Sodium Citratea) A dense white ppt was immediately formed.b) On heating, no other reaction took place. Barium Citrate, like Calcium, is a white insoluble compound.Sodium Silicatea) A WHITE ppt was formedb) No further reaction on heating or standing. Solid white Barium Silicate was formedSodium Vanadatea) 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 reactionBarium Vanadate is formed, also with the posible formation of a vanadium soluble salt which is colourless / pale yellow in colour.Potassium Dichromatea) The apparent precipitation is of an orange precipitate, however filtration had shown that the reaction formed a DENSE HIGH-LIGHTER YELLOW PPT at thebottom 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, whereasthe chrome ions were orange. Adding more barium salt to the orange filtrate didnt gave off again a ppt.Sodium Tungstatea) A MILKY WHITE ppt was formed at onceb) No further reaction on heating, standing or adding xs TungstateBarium Tungstate was precipitated as a white solid.Ammonium Molybdatea) A MILKY WHITE ppt was formedb) No further reaction on heat or standing
SEPARATION and IDENTIFICATION of STRONTIUM1. Separation of Strontium from Calcium Cr2O72 + 2NH3 + H2O 2CrO42 + 2NH4+2. Identification of Strontium- the formation of a fine yellow crystalline precipitate ofstrontium chromate confirms the presence of strontium- flame test- crimson color
IDENTIFICATION of CALCIUM• The solution from the strontium chromate separation contains the calcium ion.• The addition of ammonium oxalate precipitates calcium oxalate, CaCrO4, a white crystalline salt. Ca2+ + C2O42 CaC2O4• Flame test- brick red color
01: Sodium Hydroxidea) This gave a MILKY WHITE PPT. insoluble in exess Hydroxide b) No reaction on heating Unslouble (slightly soluble) white Calcium Hydroxide was formed.02: Ammonium Hydroxidea) 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 Hydroxide03: Sodium Carbonatea) A WHITE PPT was immediately formedb) No reaction on heating or exess Insoluble white Calcium Carbonate was immediately formed.04: Potassium Sulphatea) 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.05: Sodium Sulphite (or Sodium Metabisulphite)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 itsreaction 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 thesulphate.06: Sodium Sulphidea) 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.07: Sodium Fluoridea) 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.08: Potassium Iodatea) 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 Calciumiodate. Dont know why this was not spontanous (i.e formed as soon as the two solutions were mixed.)
09: Ammonium Phosphatea) A WHITE PPT formed at once.b) No further reaction on heating. Calcium also bears an insoluble phosphate.10: Sodium TetraBoratea) A dense WHITE PPT. was formed rapidly.b) No further reaction on heating White insoluble Calcium Borate was formed.11: Sodium Citratea) No reaction at allb) 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. Anexcellent test to distinguish between Mg and Ca for example. White insoluble Calcium Borate was formed.12: Sodium Silicatea) WHITE ppt was formed rapidly.b) No reaction on heating or standing. White Calcium Silicate was formed.13: Potassium Ferro(II)Cyanidea) No reaction or ppt detectedb) On heating a little white fine ppt was formed. Dont know if its an experimental error, but I would not rely on and perform this test.14: Sodium Tungstatea) A MILKY WHITE ppt was formed rapidly.b) No further reaction, due to heating, xstungstste or standing15: Ammonium Molybdatea) No initial precipitation or reactionb) On heating, a FAINT WHITE PPt was formed.