Recording-2025-02-27T19_59_50.929Z

Entropy and Ion Size

• The size of ions is important in understanding how they interact with water molecules.

• I^- is larger than F^-:

  • Due to increased radius, I^- leads to weaker ion-dipole interactions with water molecules.

  • This allows for more arrangements of water molecules.

• With more arrangements, the change in entropy (ΔS) is more positive.

• Hence, HI is a stronger acid than HF due to entropy considerations.

Acid-Base Reactions and Equilibrium

• In acid-base reactions, equilibrium favors the weaker side.

• Strong acids and bases react to form weaker acids and bases.

  • Example: Start with stronger acids/bases, end up with weaker counterparts at equilibrium.

• When researching a particular reaction, determine whether products or reactants are favored based on strength:

  • Stronger Acid + Stronger Base → Weaker Acid + Weaker Base

• Example Reaction: Water molecules can also react to produce H₃O⁺ and OH^-.

• If the concentration begins equal, the reaction will favor the formation of the weaker side (reactants in this case).

Identifying Acids and Bases in Reactions

• To identify acids and bases:

  • Recognize that in the reverse reaction, the species donating a proton is the acid (e.g. H₃O⁺ is the acid).

  • The species accepting a proton is the base (e.g. OH^-).

  • Remember to identify conjugate acid-base pairs in reactions.

Lewis Structures for Comparison

• Compare substances to identify which is a stronger base:

  • For example, comparisons between water and hydroxide (OH^-).

  • Hydroxide is recognized as a stronger base due to its negative charge which enhances its ability to share electrons.

Strong Acid and Base Identification

• Memorize common strong acids:

  • HCl, HBr, HI, HNO₃, H₂SO₄

  • Strong acids fully ionize in solution; anything not listed is likely a weak acid.

• Memorize strong bases:

  • Sodium hydroxide (NaOH) and similar alkali metal hydroxides fully ionize.

pH and Ion Concentration

• The pH scale indicates acidity or basicity:

  • pH = -log[H₃O⁺]: A lower pH indicates higher acidity (higher H₃O⁺ concentration).

  • In pure water, the concentration of H₃O⁺ is 1 x 10^-7 M, yielding a pH of 7.

• Beyond neutral pH (7), the solution becomes basic, with lower concentrations of H₃O⁺; below pH 7, it is acidic with higher concentrations.

Calculating pH

• To determine the pH from H₃O⁺ concentration:

  • Example: pH of 1 x 10^-2 M H₃O⁺ is 2 (acidic)

  • Example: pH of 3 x 10^-12 M H₃O⁺ is approximately 11.5 (basic)

• Understanding how pH changes with H₃O⁺ concentration is crucial for acid-base chemistry.