The reaction $Pb \left( NO _3\right)_2$ and $NaCl$ in water produces a precipitate that dissolves upon the addition of $HCl$ of appropriate concentration The dissolution of the precipitate is due to the formation of
- $PbCl _2$
- $PbCl _4$
- $\left[ PbCl _4\right]^{2-}$
- $\left[ PbCl _6\right]^{2-}$
The Correct Option is C
Approach Solution - 1
We are given the following reaction in aqueous solution:
\[ \text{Pb(NO}_3\text{)}_2 + \text{NaCl} \rightarrow \text{PbCl}_2 (\text{precipitate}) + 2 \text{NaNO}_3 \]
When the precipitate, \( \text{PbCl}_2 \), is formed and then dissolves upon the addition of HCl, this dissolution is due to the formation of a soluble complex ion.
Step 1: Precipitation of \( \text{PbCl}_2 \)
When \( \text{Pb(NO}_3\text{)}_2 \) and \( \text{NaCl} \) are mixed in water, a precipitation reaction occurs: \[ \text{Pb}^{2+} + 2 \text{Cl}^- \rightarrow \text{PbCl}_2 (s) \] Here, lead(II) chloride (\( \text{PbCl}_2 \)) forms as a white precipitate.
Step 2: Dissolution of the Precipitate
Upon adding excess HCl, the \( \text{PbCl}_2 \) precipitate dissolves, forming a soluble lead(II) chloride complex. This occurs because the chloride ions from HCl coordinate with lead ions to form a complex. The formation of the complex ion can be represented as: \[ \text{PbCl}_2 (s) + 2 \text{Cl}^- \rightleftharpoons [\text{PbCl}_4]^{2-} \] The \( [\text{PbCl}_4]^{2-} \) complex is soluble in water, which leads to the dissolution of the precipitate.
Step 3: Conclusion
The dissolution of \( \text{PbCl}_2 \) is due to the formation of the soluble \( [\text{PbCl}_4]^{2-} \) complex ion. Therefore, the correct answer is:
The correct option is C: \( [\text{PbCl}_4]^{2-} \)
Approach Solution -2
When lead ions (Pb2+) react with chloride ions (Cl−), a white precipitate of lead(II) chloride (PbCl2) forms.
This precipitate is soluble in concentrated hydrochloric acid due to formation of tetrachloroplumbate (II) ion
So the correct answer option is (C)
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Concepts Used:
P-Block Elements
- P block elements are those in which the last electron enters any of the three p-orbitals of their respective shells. Since a p-subshell has three degenerate p-orbitals each of which can accommodate two electrons, therefore in all there are six groups of p-block elements.
- P block elements are shiny and usually a good conductor of electricity and heat as they have a tendency to lose an electron. You will find some amazing properties of elements in a P-block element like gallium. It’s a metal that can melt in the palm of your hand. Silicon is also one of the most important metalloids of the p-block group as it is an important component of glass.
P block elements consist of:
- Group 13 Elements: Boron family
- Group 14 Elements: Carbon family
- Group 15 Elements: Nitrogen family
- Group 16 Elements: Oxygen family
- Group 17 Elements: Fluorine family
- Group 18 Elements: Neon family