Qualitative Analysis

The presence of Cl^- (chloride) is indicated by the observations.

Here's a breakdown:

• Reaction with Lead Nitrate: The addition of lead nitrate (Pb(NO₃)₂) to a chloride salt will produce a white precipitate of lead(II) chloride (PbCl₂):
• Solubility in Warm Water: Lead(II) chloride (PbCl₂) is unique in that it is soluble in hot water. The elevated temperature increases its solubility, causing the precipitate to dissolve:
• Reprecipitation on Cooling: As the warm water cools, the solubility of lead(II) chloride decreases, causing it to reprecipitate out of solution as a white solid.
• Other Anions:
  • Lead sulfate (PbSO₄) is also a white precipitate, but it is largely insoluble in water, even when heated.
  • Lead sulfide (PbS) is a black precipitate.
  • Lead nitrate (Pb(NO₃)₂) is soluble, so nitrate (NO₃^-) would not form a precipitate.

Therefore, the given observations strongly suggest the presence of chloride (Cl^-) ions in the original sodium salt.

Correct Answer: Cl^-