Question

The reaction of Pb(NO₃)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 ______.

Options

• PbCl₂

• PbCl₄

• [PbCl₄]²⁻

• [PbCl₆]²⁻

Answer 1

The reaction of Pb(NO₃)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 [PbCl₄]²⁻.

Explanation:

When Pb(NO₃)₂ (lead nitrate) reacts with NaCl (sodium chloride) in water:

\[\ce{Pb(NO3)2_{(aq)} + 2 NaCl_{(aq)} -> PbCl2_{(s)} + 2NaNO3_{(aq)}}\]

PbCl₂ is a white precipitate.

When HCl is added to the precipitate PbCl₂, the precipitate dissolves. This happens because:

Pb²⁺ ions react with excess Cl⁻ from HCl to form a soluble complex ion.

\[\ce{PbCl2_{(s)} + 2 HCl -> [PbCl4]^{-2}}\]

The dissolution of the precipitate is due to the formation of the tetrachloroplumbate(II) complex ion, [PbCl₄]²⁻.