Question

An unknown mixture of ions may contain the following ions: Cl^-, I^-, CO3^2-, PO4^3-, NO3^-

The following tests are performed on the unknown solution and there are the results:

i.) AgNO3 is added to the mixture and no precipitate forms.

ii.) BaCl2 is added to the mixture and no precipate forms.

Based on the results (i.) and (ii.) answer the following:

a.) Which ions (if any) are definitely identified?

b.) Which ions (if any) are definitely not in the unknown mixture?

c.) Which ions (if any) would require further tests in order to determine their presence in the unknown mxiture?

Answer 1

i) AgNO₃ solution reacts with Cl^- and I^- to form white and yellow precipitates of AgCl and AgI respectively. It also forms yellow precipitates of Ag₂CO₃ and Ag₃PO₄ with CO₃^2- and PO₄^3- ions._.As no precipitates are formed with AgNO₃, so Cl^-, I^-, CO₃^2- and PO₄^3- are definitely not present in the unknown mixture.

ii) BaCl₂ solution reacts with CO₃^2- and PO₄^3- to form precipitates of BaCO₃ and Ba₃(PO₄)₂. As no precipitation occurs in this case also, so CO₃^2- and PO₄^3- are definitely not present in the unknown mixture. BaI_{​​​​2} and BaNO₃ are water soluble. I^- is not present as per the test in (i) so NO₃^- could be present.

a) With the tests given above, there is no ion which is definitely identified.

b) With the tests above Cl^-, I^-, CO₃^2- and PO₄^3- are definitely not present in the unknown mixture.

c) For confirming presence of NO₃^- ions, further tests may be required.