Concept I - Types of Solutions and Solubility

Classification of Mixtures

• Heterogeneous Mixtures: Non-uniform distribution of particles.
      * Suspensions: Large particles that settle out unless stirred (e.g., muddy water).
      * Colloids: Intermediate particle size; appear homogeneous but scatter light via the Tyndall effect (e.g., paint).

• Homogeneous Mixtures: Uniform distribution of particles.
      * Solutions: Two parts consisting of a solute (substance dissolved) and a solvent (dissolving medium).

Properties and Types of Solutions

• Gas in gas: Oxygen in nitrogen.

• Gas in liquid: Carbon dioxide in water.

• Liquid in liquid:
      * Miscible: Liquids that dissolve freely in any proportion.
      * Immiscible: Liquids that are not soluble in each other and form layers.

• Solid in solid: Zinc in copper (forms brass, an alloy).

• Comparison Summary:
      * Solutions: Smallest particles; does not settle; cannot be filtered; no Tyndall effect.
      * Colloids: Intermediate particles; does not settle; cannot be filtered; exhibits Tyndall effect.
      * Suspensions: Largest particles; settles out; can be filtered; sometimes exhibits Tyndall effect.

Solubility Principles and Guidelines

• Solubility: Amount of substance required to form a saturated solution at a specific temperature.

• Rule: "Like dissolves like" (polar dissolves polar; nonpolar dissolves nonpolar).

• General Solubility Rules:
      * Always Soluble: Group 1 ions, $NH_4^{1+}$, $NO_3^{1-}$, $C_2H_3O_2^{1-}$, $CH_3COO^{1-}$, $HCO_3^{1-}$, and $ClO_3^{1-}$.
      * Halides ($Cl^{1-}$, $Br^{1-}$, $I^{1-}$): Soluble except with $Ag^{1+}$, $Cu^{1+}$, or $Pb^{2+}$.
      * Sulfates ($SO_4^{2-}$): Soluble except with $Ag^{1+}$, $Ca^{2+}$, $Sr^{2+}$, $Ba^{2+}$, or $Pb^{2+}$.
      * Insoluble/Specific: $CO_3^{2-}$ and $PO_4^{3-}$ are only soluble with Group 1 or $NH_4^{1+}$. $OH^{1-}$ and $S^{2-}$ are soluble with Group 1, $NH_4^{1+}$, $Ca^{2+}$, $Ba^{2+}$, or $Sr^{2+}$.

Properties of Water and the Dissolving Process

• Water: Known as the universal solvent due to polarity and strong hydrogen bonds; has high specific heat.

• Dissolution: The process of a solute being surrounded by solvent molecules.

• Dissociation: Separation of ions in an ionic compound during dissolution.

• Solvation/Hydration: Interaction between solute and solvent particles; Hydrates are ionic crystals containing water (e.g., $CuSO_4 \cdot 5H_2O$).

• Net Ionic Equations: Equations showing only ions undergoing chemical change; spectator ions are removed.
      * Example: $Zn^{2+} \, (aq) + S^{2-} \, (aq) \rightarrow ZnS \, (s)$

Electrolytes vs. Nonelectrolytes

• Electrolytes: Ionic substances that conduct electricity in aqueous solutions.
      * Strong Electrolytes: High conductivity; solutes exist almost entirely as ions (e.g., $NaCl$).
      * Weak Electrolytes: Low conductivity; small amount of dissolved compound exists as ions (e.g., $NH_4OH$).

• Nonelectrolytes: Covalent substances (like sugar $C_6H_{12}O_6$) that dissolve as molecules and do not conduct electricity.

Factors Affecting Solubility and Saturation

• Rate Factors: Surface area (smaller particles dissolve faster), agitation (stirring), and temperature.

• Temperature Effects:
      * Solids: Solubility typically increases with temperature.
      * Gases: Solubility decreases as temperature increases.

• Pressure: Henry’s Law states gas solubility is directly proportional to the partial pressure of the gas above the liquid.

• Saturation Levels:
      * Saturated: Contains maximum dissolved solute.
      * Unsaturated: Contains less than the maximum solute.
      * Supersaturated: Contains more than the theoretical maximum solute.