An unknown colorless aqueous solution might contain any of these 9 different ion

Question

An unknown colorless aqueous solution might contain any of these 9 different ions: CO3(2-), SO4(2-), CrO4(2-), Cl(-), SCN(-), Pb(2+), Ni(2+), Cu(2+), or Fe(3+). Suppose you observe the following using 3 different samples of the unknown:

- Upon addition of 6 M HCl, no change appears to have occurred.

- When 0.1 M BaCl2 is added to the acidified unknown, a clear solution results.

- When 0.5 M KSCN is added to the unknown, a deep red color appears.

QUESTIONS:

a) Which ions are certainly present in the unknown? Explain.

b) Which ions are definitely absent in the unknown? Explain.

c) Finally, for which ions in the unknown would you have to conduct more experiments to determine? What experiments would you have to conduct?

Explanation / Answer

Answer;-

(a). Cl(-) and Fe(3+) ions are certainly present in the unknown because KSCN makes deep red colored solution with Fe(3+) and addition of BaCl2 makes solution clear.

(b). Pb(2+), SO4(2-), CrO4(2-) and SCN(-) ions are certainly absent because addition of BaCl2 does not give white precipitate and addition of HCl does not give black precipitate of PbCl2 and there is no red blood color of solution due to SCN(-).

(c). CO3(2-), Cu(2+), and Ni(2+).

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