1. You are given an unknown solution that may contain Pb2+ or Ba2+, a mixture of

Question

1. You are given an unknown solution that may contain Pb2+ or Ba2+, a mixture of both or neither ion. A reasonable method for separating these ions is shown below. Pb Ba NaCl Dilute Na2 SO 4 White precipitate (indicating presence of Pb21) White precipitate (indicating presence of Ba) 2+ a. What is the precipitate formed for Pb2+? b. What is the effect, if any, of adding excess chloride in the first step of the schema? c. What is the precipitate formed for Ba2+? d. Could a solution of HCI be used in the above scheme rather than aqueous NaCI? Explain. e. Would you need to perform confirmatory tests on either of the two precipitates shown? Why or why not?

Explanation / Answer

a)

Pb+2 + Cl- ions --> PbCl2(s)

since chloride ions of Lead are not soluble

b)

in excess Cl- ions:

PbCl2 dissolves due to the formation of a complex ion

tetrachloroplumbate(II) ion

PbCl2(s) + 2Cl-(aq) <==> [PbCl4]2-(aq)

c)

Ba+2 + SO4-2 --> BaSO4(s)

all barium sulfates are not soluble

d)

Not really... since Chlorine should precipitate only Pb ions...

even though if not all 100% Pb precipitate, then you could have PbSO4 which is not soluble

so you will want to confirm this is not PbSO4 when adding SO4-2 ions for BaSO4

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