102 5. In analyzing an unknown, why is it reasonable to test for Ca?, Mg and A b

Question

102 5. In analyzing an unknown, why is it reasonable to test for Ca?, Mg and A before testing (by precipitation) for k*? 6. You are told that an unknown solutton can contafn only AT(H20, Mg (H20)6 a) Suggest two reagents (include concentration) where each of them, if used care b) Considering each of your suggested reagents one at a time, would 1t be useful Ca, and NO ions. fully, could precipitate a11 of the metallic ions? by itself in detecting and/or distinguishing between Ca and A(H206if you knew that only one of these ions was present in the solution? How? (Make sure that you discuss each reagent that you have suggested in enough detail.) 7. Of the cations studied so far, the only cation that is not "soluble" when com- bined with sulfate ion is calclum-partially soluble Cas04 2H20 forms. Hould a reagent containing the sulfate ion (decide on a specific reagent) be the best way (most likely to result in a precipitate) to test for Cat in a solu tion of an Unknown 2. Why/why not?

Explanation / Answer

5. Among the given ions, all respond to the flame test by imparting varying colours to the flame that are extremely difficult to distinguish to all but the trained eye. But except potassium ion, all others can be selectively precipitated from the medium by using reagents specific for each ion. Now after precipitation if the flame test is performed, the only change in flame colour can be attributed to the non-precipitable potassium ions thus eliminating all other factors which can mask its presence.

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