Acids and Bases: Definitions and Properties

This document comprehensively covers the concepts of acids and bases, detailing their properties, dissociation, classifications, and key theories.

Properties of Acids and Bases

Acids

• Litmus Paper Test: Turns litmus paper red.

• Taste: Sour note.

• Reactivity: React vigorously with metals, causing them to dissolve and often releasing hydrogen gas.

• Conductivity: Conducts electricity when dissolved in water.

• Corrosiveness: They can be corrosive to materials and tissue.

• Chemical Formation: Produce hydronium ions ($H_3O^+$) in solution.

• Proton Donors (Brønsted-Lowry): Defined as substances that donate protons (hydrogen ions).

Bases

• Litmus Paper Test: Turns litmus paper blue.

• Taste: Bitter.

• Feel: Slippery texture.

• Conductivity: Conducts electricity in solution.

• Corrosiveness: Can also be corrosive.

• Chemical Formation: Produce hydroxide ions ($OH^-$) in solution.

• Proton Acceptors (Brønsted-Lowry): Defined as substances that accept protons.

Dissociation of Acids and Bases

• Definition: The process where an ionic compound breaks apart into its constituent ions when dissolved in water.

• **Dissociation equations:
    1. *Sodium Hydroxide:*
       $NaOH <br>ightarrow Na^+ + OH^-$
    2. Calcium Hydroxide:
       $Ca(OH)_2 <br>ightarrow Ca^{2+} + 2OH^-$
    3. Hydrochloric Acid:
       $HCl <br>ightarrow H^+ + Cl^-$
    4. Carbonic Acid:
       $H_2CO_3 <br>ightleftharpoons H^+ + HCO_3^-$

Strong vs Weak Electrolytes/Acids/Bases

Strong Acids/Bases

• Completely dissociate in water.

• Examples:
    - Strong Acid: Hydrochloric Acid, $HCl$.
    - Strong Base: Sodium Hydroxide, $NaOH$.

Weak Acids/Bases

• Partially dissociate in water.

• Example:
    - Weak Acid: Acetic Acid, $CH_3COOH$.
    - Weak Base: Ammonia, $NH_3$.

• In equilibrium, only a few $H^+$ or $OH^-$ ions are released.

Theories of Acids and Bases

Arrhenius Theory

Arrhenius Acids

• Definition: Any substance that, when added to water, increases the concentration of hydronium ions ($H_3O^+$).

• Ionizable Hydrogens: Count the number of ionizable hydrogens in a compound to predict how many $H_3O^+$ ions will form.

• Examples:
    - Hydrochloric Acid, $HCl$.
    - Sulfuric Acid, $H_2SO_4$.

Arrhenius Bases

• Definition: Any substance that, when added to water, increases the concentration of hydroxide ions ($OH^-$).

• Hydroxide Count: The number of hydroxide ions in the formula indicates how many $OH^-$ ions will be produced.

• Examples:
    - Sodium Hydroxide, $NaOH$.
    - Calcium Hydroxide, $Ca(OH)_2$.

Limitations of Arrhenius Theory

• Only applicable to aqueous solutions.

• Cannot classify amphoteric substances that can act as either acids or bases depending on the context.

Brønsted-Lowry Theory

Brønsted-Lowry Acids

• Definition: Substances that donate protons.

• Example Reaction:
    1. $HCl <br>ightarrow H^+ + Cl^-$
    2. $H^+ + H_2O <br>ightarrow H_3O^+$

• Analysis: Hydrochloric acid ($HCl$) is classified as both an Arrhenius acid (produces $H_3O^+$) and a Brønsted-Lowry acid (donates a proton).

Brønsted-Lowry Bases

• Definition: Substances that accept protons.

• Example:
    - Ammonia ($NH_3$) acts as a proton acceptor and produces $OH^-$ in water, thus fulfilling the Arrhenius base criteria.

Classification Overlap

• Arrhenius acids and bases are inherently Brønsted-Lowry acids and bases.

• Conversely, Brønsted-Lowry acids and bases are not always classified within the Arrhenius framework.

Conjugate Acids and Bases

• Definition:
    - When an acid loses a proton, it becomes a conjugate base.
    - When a base gains a proton, it becomes a conjugate acid.

• Practice Problems:
    - Write the conjugate base of Hydrofluoric Acid ($HF$). The answer is $F^-$.
    - Write the conjugate acid of Nitrate ($NO_3^-$). The answer is $HNO_3$.

• General Rule: Every acid has a corresponding conjugate base, and every base has a corresponding conjugate acid derived from proton transfer reactions.
  

Reversibility of Acid/Base Reactions

• Observation: Reactions can be reversed to identify alternate acids and bases, but the acid/base pairs remain consistent.

Example of Acid/Base Reaction

• $HCl + H_2O <br>ightarrow H_3O^+ + Cl^-$

Amphoteric Substances

• Definition: Compounds that can act as either an acid or a base depending on the context; they can both donate and accept protons.

• Example: Water ($H_2O$) is amphoteric as it can act as either:
    - Acid: $HCO_3^- + H_2O <br>ightarrow H_2CO_3 + OH^-$
    - Base: $HCO_3^- + H_2O <br>ightarrow CO_3^{2-} + H_3O^+$

• Other Example: Hydrogen carbonate ($HCO_3^-$) can function both ways based on its interaction with other substances.