Why do the premininary tests not help in theidentftificatin of nitrate and nitri

Question

Why do the premininary tests not help in theidentftificatin of nitrate and nitrite?

2. A student analyzes a sample using the prelininarytests and finds that no precipitate is obtained upon the additionof silver ion but a precipitate is observed on the addition ofbarium ion. Which individual ion tests should be used todetermine the anions present in this sample?

3. In the preliminary tests 3 HNO3is added to the precipitate of the silver group. If a yellowprecipitate remains, what ion is probably present?

4. Why can't a fresh sample of unknown solution be usedfor the individual ion test for sulfite?

5. Describe the specific tests that would need to becarried out on an unknown sample suspected of containing carbonate,sulfate, and iodide:

Explanation / Answer

both give brown fumes ine with dil h2so4 and conc h2so4 hence it would be tough to come to any specific conclusion. Colourless gas with the smell of rotten eggs is evolved which turns lead acetate paper black. Colourless gas with a pungent smell, like burning sulphur which turns acidified potassium dichromate solution green. Brown fumes which turn acidified potassium iodide solution containing starch solution blue. CO2 H2S SO2 NO2 Carbonate ( 2– 3 CO ) Sulphide (S2– ) Sulphite ( 2– SO3 ) sulphate ion is present, brium gives white precipitate. A dirty green precipitate is formed with sodium hydroxide solution. Bright yellow flame test. Lilac flame test. Dissolve in nitric acid, then add barium chloride solution which gives a white precipitate. PbCl2 is by far the most soluble of the three in water. Therefore, the first step in separating the three chlorides is to treat the solid mixture with hot water to selectively dissolve PbCl2 and to leave AgCl and Hg2Cl2 as a solid mixture. Once Pb2+ is back in aqueous solution, the presence of this ion in this solution can be confirmed by the addition of potassium chromate, K2CrO4. The Pb2+ ion and the chromate ion, CrO4 2-, combine to form the bright yellow, insoluble solid lead(II) chromate, PbCrO4. Pb2+(aq) + CrO4 2-(aq) PbCrO4(bright yellow solid) Silver(I) and mercury(I) chlorides are too insoluble in water to be redissolved in water, even when the water is boiled. Therefore, we turn to another useful trick for dissolving precipitates: we take advantage of the tendency of transition metal ions such as Ag+ to form water-soluble complex ions with ammonia, NH3. Here the ammonia uses the lone pair of electrons of the N atom to form a bond with the Ag+ ion. this is beacause both sulphate and ulphite give precipitate, hence the result will be incnclusive. the following are the tests that should eb carried to find out ablout the carbonate sulphite and iodide. Colourless gas with the smell of rotten eggs is evolved which turns lead acetate paper black. Colourless gas with a pungent smell, like burning sulphur which turns acidified potassium dichromate solution green. Brown fumes which turn acidified potassium iodide solution containing starch solution blue. CO2 H2S SO2 NO2 Carbonate ( 2– 3 CO ) Sulphide (S2– ) Sulphite ( 2– SO3 ) A colourless, odourless gas is evolved with brisk effervescence, which turns lime water milky. Colourless gas with the smell of rotten eggs is evolved which turns lead acetate paper black. Colourless gas with a pungent smell, like burning sulphur which turns acidified potassium dichromate solution green. Brown fumes which turn acidified potassium iodide solution containing starch solution blue. CO2 H2S SO2 NO2 Carbonate ( 2– 3 CO ) Sulphide (S2– ) Sulphite ( 2– SO3 )

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