3.10+Solubility

3.10 Solubility

Enduring Understanding

  • SPQ-3: Interactions between intermolecular forces influence the solubility and separation of mixtures.

Learning Objective

  • SPQ-3.C: Explain the relationship between the solubility of ionic and molecular compounds in aqueous and nonaqueous solvents and the intermolecular interactions between particles.

Solubility

  • Definition: Solubility refers to the extent to which a solute dissolves in a solvent to form a solution.

    • Highly Soluble: When a large amount of solute can dissolve.

    • Slightly Soluble: When only a small amount of solute dissolves.

    • Insoluble: When no solute dissolves.

Aqueous Solutions

  • Water as a Solvent: Water is commonly used because it dissolves many substances due to its properties.

  • Polarity: Water is a highly polar molecule, with a partial positive charge on hydrogens and a partial negative charge on the oxygen due to lone pairs on oxygen.

Hydration

  • Definition: Hydration is the process in which water molecules surround and dissolve ions.

  • Ion-Dipole Interaction: Water molecules orient themselves so that the positive ends face negative ions and the negative ends face positive ions, facilitating dissolution.

  • Hydrated Ions: When ionic solids dissolve in water, they become hydrated.

Dissolution of Polar Solids

  • Example: Water can also dissolve non-ionic substances like acetic acid (CH3COOH).

    • The –O-H group in acetic acid forms hydrogen bonds with water, allowing it to dissolve without breaking apart like ionic compounds.

Like Dissolves Like

  • Rule: "Like dissolves like" conveys that substances with similar intermolecular forces (IMFs) are more likely to dissolve in each other.

    • Polar Substances: Dissolve in polar solvents.

    • Nonpolar Substances: Dissolve in nonpolar solvents.

    • Incompatibility: Nonpolar substances do not dissolve in polar solvents due to insufficient energy retrieval from interactions.

Steps of Solution Formation

  1. Solute Particle Separation: Energy is required to separate solute particles.

  2. Solvent Particle Separation: Energy is required to separate solvent particles.

  3. Solute and Solvent Interaction: Energy is released when solute and solvent particles combine.

  • Energy Considerations: The energy involved varies with the strength of IMFs.

Miscibility

  • Miscible: Two substances that mix well (e.g., vinegar and water).

  • Immiscible: Two substances that do not mix (e.g., oil and water).

Practice Activity

  • For the substances listed, determine the type(s) of IMF present and whether they will dissolve better in hexanes (C6H14) or water (H2O):

    • NaCl

    • C3H8

    • CO2

    • CH2O

Review Activity

  • Molecular Level Diagram Task: Diagram the reaction:

    • Pb2+(aq) + 2NO3-(aq) + 2Na+(aq) + 2Cl-(aq) → PbCl2(s) + 2Na+(aq) + 2NO3-(aq)

    • Include solutions before and after the reaction and include a key.