3. In analyzing an unknown salt containing one of the anions discussed in this m

Question

3. In analyzing an unknown salt containing one of the anions discussed in this module, a student obtains negative results for all three classification reactions. Briefly explain. 4. A solution is known to contain at least one of the anions discussed in this module. (1) The yellowish precipitate that forms when AgNO, solution is added to the solution dissolves when HNOs is added. Which anion(s) may be present? A BaCl, solution is added to this solution. A white precipitate forms that dissolves when HNO, is added. No color, odor, or evolved gas is observed. Which anion is present? Describe a confirmatory reaction for this anion. (2) In some of the classfication reactions, it is important when there is no reaction upon addition of a second reagent. For which anions is this true? . In some of the classif

Explanation / Answer

4) it may contain these anions  Br^-, CO3^2-, Cl^-, I^-. NO3^-, NO2^-, PO4^3-, SO4^2-, and SO3^2-

1.)PO4(3-)
with silver nitrate solution a yellow precipitate of silver orthophosphate Ag3Po4 is formed which is soluble in dilute ammonia and in dilute nitric acid...
i am giving the net ionic eqn for the three cases...
Po4(3-) + 3Ag(+) -----> Ag3Po4
Ag3Po4 + 6Nh3 ------> 3[Ag(Nh3)2](+) + Po4(3-)
Ag3Po4 + 2H(+) -------> H2Po4(-) + 3Ag(+)

2)both phosphate(Po4^3-) and carbonate(Co3^2-) give white precipitate with Bacl2 forming barium phosphate and barium carbonate respectively and both are soluble in HNo3...
2PO4(3-) + 3Ba (2+) -----> Ba3(Po4)2
Co3(2-) + Ba(2+) ----->BaCo3
but carbonate gives vigouros effervescence with Hno3...so it is not the anion according to your conditions...
CO32-(aq or s) + 2H+(aq) ------->H2O(l) + CO2(g)
so phosphate is the answer
i am not sure about the confirmatory test but i will try... i hope this is right...
when ammonium molybdate is treated with a solution containing phosphate a yellow crystalline precipitate of ammonium phosphomolybdate is formed ....
Po4(3-) + 3Nh4(+) +12MoO4(2-) +24H+ -------> (Nh4)3[P(Mo3O10)4] + 12H2o

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