Chapter 18, Problem 64E

Interpretation Introduction

Interpretation:

In the qualitative cation analysis for 1.00 mL of the saturated ${\text{PbCl}}_{\text{2}}\left(aq\right)$ at $25{}^{\circ }\text{C}$, the presence of sufficient Pb²⁺to produce a precipitate of PbCrO₄(s) needs to be shown.

Concept introduction:

When a solution is treated with HCl and a precipitate is formed, one or more of these cations may be present in the solution; Pb²⁺, Hg₂²⁺, Ag⁺. To identify these individual cations, the precipitate is filtered and the dried precipitate is further subjected to testing.

PbCl₂ is more soluble than other two precipitates; Hg₂Cl₂ and AgCl. When the temperature increases, solubility of a solid increases. So, when the precipitate obtained from group 1 analysis is washed with hot water, PbCl₂ precipitate dissolves in hot water and only Hg₂Cl₂ and AgCl remains as precipitates. Presence of Pb²⁺ can be identified by adding a CrO₄^2- solution. When Pb²⁺ reacts with CrO₄^2-, it forms a yellow color precipitate PbCrO₄.