Question

In a group 1 analysis, a student obtained a precipitate containing both \(\mathrm{AgCl}\) and \(\mathrm{PbCl}_{2}\). Suggest one reagent that would enable the student to separate \(\mathrm{AgCl}(s)\) from \(\mathrm{PbCl}_{2}(s)\)

Short answer

Use hot water to dissolve PbCl₂, separating it from AgCl.

Step-by-step solution

Understand Solubility Differences

AgCl and PbCl₂ have different solubility characteristics in hot water. While AgCl is poorly soluble in both hot and cold water, PbCl₂ is more soluble in hot water.

Select the Reagent Based on Solubility

To separate AgCl and PbCl₂, we can use hot water to dissolve PbCl₂. This separation takes advantage of the higher solubility of PbCl₂ in hot water compared to AgCl.

Apply the Reagent

Add hot water to the mixture of AgCl and PbCl₂. Stir the mixture to ensure that PbCl₂ dissolves into the hot water, while AgCl remains as a solid.

Perform Separation

Filter the solution. The hot water will contain dissolved PbCl₂, while AgCl will remain as a solid on the filter paper. This process effectively separates AgCl from PbCl₂.

Key concepts

Solubility Differences

Solubility differences arise when different substances exhibit varying abilities to dissolve in particular solvents like water. These differences are crucial in many separation techniques because they determine how substances can be selectively dissolved out of a mixture. For instance, silver chloride (\(\mathrm{AgCl}\)) has low solubility in water whether the water is hot or cold. Conversely, lead(II) chloride (\(\mathrm{PbCl_2}\)) becomes significantly more soluble in hot water, even though it's also relatively insoluble in cold water.
This property allows chemists to use temperature changes as a method of separating components of a mixture based on their solubility characteristics. By carefully selecting the correct conditions, one can selectively dissolve one component while leaving the other behind. This principle underlies many practical applications in laboratory settings and industrial processes.

Group 1 Analysis

Group 1 analysis refers to the systematic approach used in qualitative chemical analysis to identify and separate cations within the first group of metals. This group primarily includes ions that form insoluble chlorides, such as silver ion (\(\mathrm{Ag^+}\)), lead ion (\(\mathrm{Pb^{2+}}\)), and mercury(I) ion (\(\mathrm{Hg_2^{2+}}\)).
The process involves adding reagents that cause specific precipitation reactions. Due to the nature of group 1 ions, they can be initially precipitated out together as chlorides by adding hydrochloric acid. Subsequently, further treatment and analysis rely on exploiting different chemical properties such as variable solubility in selected solvents to achieve separation and identification.

• This method is a fundamental part of classical qualitative analysis schemes in chemistry.
• It's particularly useful in educational settings for teaching practical laboratory separation techniques.
• This type of analysis forms the basis for more advanced comprehension of analytical chemistry concepts.

Precipitate Separation

Precipitate separation is a critical laboratory technique involving the separation of solid particles (precipitates) from a liquid mixture. It often relies on differences in physical or chemical properties among the components of a mixture. In our scenario involving \(\mathrm{AgCl}\) and \(\mathrm{PbCl_2}\), these compounds are initially present as a mixed precipitate.
To separate \(\mathrm{AgCl}\) from \(\mathrm{PbCl_2}\), understanding each compound's solubility differences becomes key. By heating the mixture with hot water, \(\mathrm{PbCl_2}\) dissolves, whereas \(\mathrm{AgCl}\) does not. This forms the basis for dividing the components into distinct phases using simple filtration.

• The process often involves steps like washing, decanting, and using solvents selectively.
• Using a filter paper can aid in capturing the remaining solid particles after one of the components is dissolved.
• This is a fundamental exercise in separation based on solubility differences, often taught in basic chemistry labs.

Hot Water Solubility

Hot water solubility refers to how a substance's ability to dissolve in water changes with an increase in temperature. Generally, increased temperature enhances the solubility of solids in liquids, which is not always the case for all solutes but holds true for many ionic compounds.
In the context of \(\mathrm{PbCl_2}\) and \(\mathrm{AgCl}\), hot water becomes a selective solvent that can be used to dissolve \(\mathrm{PbCl_2}\) while leaving \(\mathrm{AgCl}\) undissolved. This is due to the nature of the compounds' crystal lattice energies and solvation dynamics with the water molecules. Such selective solubility is particularly useful in practical separation techniques where the aim is to isolate one component from a mixture while maintaining others in solid form.

• This technique highlights the relationship between temperature and solubility, offering insights into thermodynamic principles.
• The method is straightforward, requiring only heat application and subsequent filtration of the soluble component.
• Understanding this principle is crucial for efficient laboratory manipulations in both educational and industrial chemistries.