Chapter 15.1

Exam 2 Material - Chapter 15: Solutions of Acids and Bases

Definitions of Acids and Bases

• Arrhenius Acid:

  • Any substance that produces $H^+$ when dissolved in water.

• Arrhenius Base:

  • Any substance that produces $OH^-$ when dissolved in water.

• Note: Arrhenius acids and bases are restricted to aqueous solutions.

Learning Objectives

• Define Brønsted-Lowry acids and bases.

• Differentiate between Brønsted-Lowry and Arrhenius acids and bases.

• Identify conjugate acid-base pairs.

• Identify the proton transfer in Brønsted-Lowry acid-base reactions.

Strong Acids and Bases

• Strong Acids and Bases:

  • Classified as strong electrolytes.

  • Dissociate or ionize completely (100%) in solution.

• Examples of Strong Acids and Bases:

  • $ext{HCl (aq)} <br>ightarrow H^+ (aq) + Cl^- (aq)$

  • $ext{NaOH (s)} <br>ightarrow Na^+ (aq) + OH^- (aq)$

Weak Acids and Bases

• Weak Acids and Bases:

  • Classified as weak electrolytes.

  • Do NOT ionize completely in solution.

• Example of Weak Acid:

  • $ext{HF (aq)} <br>ightleftharpoons H^+ (aq) + F^- (aq)$

  • 99% remain as HF and 1% dissociates.

Brønsted-Lowry Acid-Base Theory

• Brønsted-Lowry Acid:

  • Defined as a proton (H+) donor.

• Brønsted-Lowry Base:

  • Defined as a proton (H+) acceptor.

• Key Feature:

  • Brønsted-Lowry acid-base reactions involve the transfer of a proton (H+) from an acid to a base.

  • This definition is broader and not limited to aqueous solutions.

Proton Exchange in Reactions

• In aqueous solutions, the following terms are used interchangeably:

  • Proton

  • $H^+ (aq)$ (hydrogen ion)

  • $H_3O^+ (aq)$ (hydronium ion)

Conjugate Acid-Base Pairs

• Definition:

  • Molecules or ions that differ by a single proton (H+).

• Characteristics:

  • The acid contains the proton (H+) that is transferred to a molecule or ion.

  • The conjugate base is the molecule or ion remaining after the loss of the proton (H+).

  • Example:

  • $HA <br>ightarrow A^-$

  • Here, HA is an acid, and A^- is its conjugate base.

• Conjugate Nation:

  • Every acid turns into its conjugate base after donating a proton.

  • Every base turns into its conjugate acid after accepting a proton.

Examples of Brønsted-Lowry Reactions

• Sample Reaction:

  • $ext{HF (aq)} + ext{H}<em>2 ext{O}( ext{l}) ightleftharpoons F^-(aq) + H</em>3O^+(aq)$

  • In this case, HF donates a proton to water.

  • Reverse reaction:

  • $F^-(aq) + H<em>3O^+(aq) ightleftharpoons ext{HF (aq)} + ext{H}</em>2 ext{O}( ext{l})$

Amphoteric Substances

• Amphoteric Substances:

  • Can act as both an acid and a base.

  • Examples include $ext{H}<em>2 ext{O}$ and $ext{HSO}</em>4^-$.

• Note: In this class, only $ext{H}_2 ext{O}$ is designated as the amphoteric molecule we will study.

Monoprotic Acids and Bases

• Until noted otherwise, all acids and bases are considered monoprotic, meaning they transfer only one proton (H+).

General Acid-Base Reaction Equation

• Reaction Form:

  • $ext{acid} + ext{base} <br>ightleftharpoons ext{conjugate base} + ext{conjugate acid}$

• Examples of Acid-Base Reactions:

  • $ext{HF} + ext{NH}<em>3 ightleftharpoons F^- + ext{NH}</em>4^+$

  • $ext{HNO}<em>2 + ext{H}</em>2 ext{O} <br>ightleftharpoons ext{NO}<em>2^- + ext{H}</em>3 ext{O}^+$

  • $ext{H}<em>2 ext{O} + ext{NH}</em>2^- <br>ightleftharpoons ext{OH}^- + ext{NH}_3$

Additional Questions on Conjugate Acid-Base Pairs

• Exercise:

  • Write the formula for the conjugate acid of $ext{PO}_4^{3-}$.

  • Write the formula for the conjugate base of $ext{HClO}$.

• Example Conjugate Pairs:

  • From base to conjugate acid:

  • Base: $ext{PO}_4^{3-}$

  • Conjugate Acid: $ext{HPO}_4^{2-}$

  • From acid to conjugate base:

  • Acid: $ext{HClO}$

  • Conjugate Base: $ext{ClO}^-$

Identifying Conjugate Acid-Base Pairs in Reactions

• Example Reactions:

  • $ext{HCN(aq)} + ext{H}<em>2 ext{O}( ext{l}) ightleftharpoons ext{H}</em>3 ext{O}^+(aq) + ext{CN}^-(aq)$

  • $ext{CH}<em>3 ext{NH}</em>2(aq) + ext{H}<em>2 ext{O}( ext{l}) ightleftharpoons ext{CH}</em>3 ext{NH}_3^+(aq) + ext{OH}^-(aq)$

  • Each reaction highlights the transfer and identification of conjugate pairs.