Solubility Notes

Introduction to Solubility

Basic Definitions

  • Solute: The stuff that gets dissolved.

  • Solvent: The stuff that does the dissolving.

  • Solution: What you get when the solute mixes into the solvent.

Examples of Solutions in Different States of Matter (Table 8.1)

  • Solid in Solid:

    • Steel: Has a bit of carbon mixed in with iron.

  • Solid in Liquid:

    • Seawater: Has salt and other stuff mixed in water.

  • Solid in Gas:

    • Mothballs: They evaporate and mix with the air, which keeps moths away.

Solubility

  • Definition: How much of a solute can dissolve in a solvent at a certain temperature. Usually measured in grams per milliliter (g/mL).

    • Slightly soluble: Not much dissolves.

    • Soluble: A good amount dissolves.

    • Insoluble: Almost nothing dissolves.

Types of Solutions

  • Unsaturated: You can still add more solute and it will dissolve.

  • Saturated: You can't add any more solute; it won't dissolve.

  • Supersaturated: Has more solute dissolved than it should at that temperature; might form crystals.

Crystallization

  • Definition: When solids form out of a supersaturated solution as it cools down.

  • You need a tiny crystal to start the process.

Solubility and Dissolving

  • Solubility: How much stuff dissolves at a certain temperature (like 36 g of salt in 100 mL of water).

  • Dissolving: When the solute breaks apart and mixes with the solvent.

Solubility Rules for Ionic Compounds in Water (Table 8.3)

  • General Rule: If a compound dissolves well (at least 1 g/100 mL of water), we say it's soluble.

  • Usually Soluble:

    • Alkali metal ions (Li+, Na+, etc.)

    • Hydrogen ion (H+)

    • Ammonium ion (NH₄+)

    • Nitrate (NO₃-)

    • Ethanoate (acetate) (CH₃COO-)

  • Exceptions for Chlorides, Bromides, and Iodides:

    • Don't dissolve well with Ag+, Pb2+, etc.

  • Exceptions for Fluorides:

    • Don't dissolve well with Mg2+, Ca2+, etc.

  • Exceptions for Sulfates:

    • Don't dissolve well with Ca2+, Sr2+, etc.

  • Sulfides:

    • Dissolve well with Alkali ions and H+, NH₄+, Be2+, Mg2+, Ca2+, Sr2+, Ba2+

    • Don't dissolve well with others

  • Hydroxides:

    • Dissolve well with Alkali ions and H+, NH₄+, Sr²+, Ba²+, Tl+

    • Don't dissolve well with others

  • Phosphates, Carbonates, and Sulfites:

    • Dissolve well with Alkali ions and H+, NH₄+

    • Don't dissolve well with others

"Like Dissolves Like" Principle

  • Polar stuff dissolves in polar stuff because they attract each other.

  • Nonpolar stuff dissolves in nonpolar stuff because they don't have charges.

  • Soap can dissolve in both because it has polar and nonpolar parts.

Dissolving by Hydration

  • Water is attracted to ions and breaks them apart.

  • Water surrounds the ions and spreads them out.

  • Not all ionic compounds dissolve in water.

Factors Affecting Solubility of Ionic Compounds

  1. Ionic Radius: Bigger ions usually dissolve better.

  2. Charge: More charge usually makes it harder to dissolve.

Ion Orientation in Water

  • The positive side of water faces negative ions.

  • The negative side of water faces positive ions.

Salt vs. Sugar Dissolved in Water

  • Salts (Ionic Compounds): Break into ions when dissolved.

  • Sugar (Molecular Compounds): Stay as molecules when dissolved.

Molecular Compounds and Solubility

  • Polar molecules stick together; if water pulls them apart, they dissolve.

  • Nonpolar molecules don't dissolve in water.

  • Bigger nonpolar parts make it harder to dissolve (e.g., ethanol vs. methanol).

Factors Affecting the Rate of Dissolving

  1. Surface Area: Smaller pieces dissolve faster.

  2. Agitation: Stirring helps it dissolve faster.

  3. Temperature:

    • Hotter temperatures help things dissolve faster.

Temperature and Pressure Effects on Solubility

  • Solids: Hotter (↑T) means more dissolves (↑S).

  • Liquids: Temperature and pressure don't matter much.

  • Gases:

    • Hotter (↑T) means less dissolves (↓S).

    • More pressure (↑P) means more dissolves (↑S).

Solubility Curves

  • Graphs that show how much solute dissolves in 100 mL of water at different temperatures.

  • The steeper the line, the more the temperature affects solubility.

Interpreting Solubility Curves

  • Unsaturated Region: Below the line.

  • Saturated Region: On the line.

  • Supersaturated Region: Above the line.

Questions from Solubility Curve Graph

  • Which salt dissolves the least at 0°C?

  • At what temperature does $$K