Verified Answer :

  • A precipitate is an insoluble solid that forms when two solutions react.
  • Potassium nitrate (\(\text{KNO}_3\)) is soluble in water, so it does not form a precipitate.
  • Silver chloride (\(\text{AgCl}\)) is insoluble in water and is a common precipitate.
  • Therefore, the substance that forms a precipitate is \(\boxed{\text{AgCl}}\).

Explanation

  1. Understanding Precipitation

To identify the product that forms a precipitate, we first define what a precipitate is. A precipitate is an insoluble solid that emerges from a liquid solution, typically occurring during a double displacement reaction where ions in aqueous solution combine to form an insoluble ionic compound. To determine which of the given products forms a precipitate, we must evaluate the solubility of each substance in water using standard solubility rules.

  1. Analyzing the Solubility of the Options

We examine the options provided:

  • \(\text{KNO}_3\) (Potassium nitrate): According to general solubility rules, all salts containing the nitrate ion (\(\text{NO}_3^-\)) are soluble. Furthermore, salts containing Group 1 metal cations, such as potassium (\(\text{K}^+\)), are also generally soluble. Since both ions are highly soluble, \(\text{KNO}_3\) will remain in solution and not form a precipitate.
  • \(\text{AgCl}\) (Silver chloride): Solubility rules state that while most chloride salts are soluble, halides of silver (\(\text{Ag}^+\)), lead, and mercury are exceptions and are generally insoluble in water. Thus, \(\text{AgCl}\) will form an insoluble solid, which constitutes a precipitate.
  • \(\text{AgK}\): This is not a stable ionic compound typical of aqueous reactions and does not fit the criteria for a standard ionic precipitate.
  • "no precipitate formed": Since \(\text{AgCl}\) is known to be an insoluble solid, this option is incorrect.
  1. Conclusion

Based on the solubility rules, \(\text{AgCl}\) is the only substance among the choices that is consistently characterized as insoluble in water. Therefore, in a reaction where silver ions and chloride ions are present in solution, \(\text{AgCl}\) will precipitate out as a solid. The final answer is \(\text{AgCl}\).

Examples

In laboratory settings, chemists use precipitation reactions to identify specific ions in an unknown sample. For example, if you suspect a solution contains silver ions (\(\text{Ag}^+\)), you can add a small amount of table salt (sodium chloride, \(\text{NaCl}\)) to it. If a cloudy white solid, which is \(\text{AgCl}\), forms, you have successfully confirmed the presence of silver ions in your solution. This technique is fundamental in analytical chemistry for both identification and purification processes.

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