Acids and Bases

Acids

Definition & Composition

  • Anhydrous acids: composed of covalent molecules; can exist in any state at room temperature.

  • All acids contain Hydrogen (H) in their formula and can ionize in water.

Ionization in Water

  • Acids break into ions when added to water: H⁺ ions + anion from the acid.

  • H⁺ ions attach to water to form Hydronium ions (H₃O⁺).

General Properties of Aqueous Acids

  • Sour taste

  • pH < 7

  • Turns blue litmus red

  • Corrosive

  • Electrolytes

Chemical Reactions

  • All acids form H⁺ ions in water, making reactions predictable.

  • H⁺ can be replaced by metal or ammonium ions to form salts.

Reactions of Acids

  1. With Metals, Carbonates, and Hydrogen Carbonates

    • Produces salt + CO₂ + H₂O

    • Observable: bubbling due to CO₂ release

  2. With Bases

    • Produces salt + water

    • Reaction called neutralization

    • Releases a fair amount of heat

Bases (Alkalis)

Definition & Composition

  • Typically metal oxides or hydroxides.

  • Can also be defined as proton acceptors.

  • Alkali: a base that dissolves in water to produce OH⁻ ions.

General Properties of Aqueous Bases

  • Bitter taste

  • Turns red litmus blue

  • Feels soapy

  • Corrosive

  • Electrolytes

Chemical Reactions

  • Neutralization with acids → salt + water

  • Bases are metallic oxides or hydroxides

  • Reactions release heat

Weak Acids and Bases

  • Do not fully ionize in solution.

  • Strength comparison: Ka (acid) and pKa

    • Higher Ka → stronger acid

    • Lower pKa → stronger acid

Buffers

Definition

  • Solution that resists pH change when small amounts of acid or base are added.

  • Composed of:

    • Weak acid + its conjugate base, or

    • Weak base + its conjugate acid

  • Example: blood uses bicarbonate/carbonic acid due to CO₂ absorption

How Buffers Work

  1. Weak acids donate H⁺, forming conjugate base

  2. Weak bases accept H⁺, forming conjugate acid

  3. Equilibrium shifts to maintain balance when species are consumed

Buffer Calculations

  • Henderson-Hasselbalch Equation:

    pH=pKa+log⁡[Conjugate Base][Acid]\text{pH} = \text{pKa} + \log \frac{[\text{Conjugate Base}]}{[\text{Acid}]}pH=pKa+log[Acid][Conjugate Base]​

  • Applications:

    • Calculate pH of buffer

    • Determine concentration of species in buffer

Buffer Capacity

  • Maximum amount of acid/base a buffer can neutralize before losing effectiveness.

Quick Recap

  • Acids: Sour, pH < 7, H⁺ ions, turn blue → red, electrolytes, corrosive

  • Bases: Bitter, pH > 7, OH⁻ ions, turn red → blue, electrolytes, corrosive

  • Neutralization: Acid + Base → Salt + Water (+ heat)

  • Weak acids/bases: Partial ionization; use Ka/pKa

  • Buffers: Resist pH change; composed of conjugate acid/base pairs