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Acid Base Theories

Learning Objectives

• Personal learning goals:
    - About both the Arrhenius and Bronsted-Lowry theories for identifying acids and bases.

• Student Success Criteria:
    - I will be successful if I can:
      - Identify an Arrhenius acid and base.
      - Identify a Bronsted-Lowry acid and base.
      - Identify the acid, base, conjugate acid, and conjugate base for an acid-base reaction.

Acid and Base Theories

Arrhenius Theory

• Definition of Acids:
    - A substance that contains $H^+$ and ionizes in water to produce $H^+$ (or $H_3O^+$).
      - Example:
        - $HCl + H_2O <br>ightarrow H_3O^+ + Cl^-$

• Definition of Bases:
    - A substance that contains $OH^-$ and dissociates in water to produce $OH^-$.
      - Example:
        - $NaOH <br>ightarrow Na^+ + OH^-$

Arrhenius Theory Limitations

• Can only classify compounds with $OH^-$ as a base.

• Can only be applied to reactions in water.

• Would incorrectly classify substances:
    - For instance, ammonia ($NH_3$) could not be classified as a base despite being a base because it does not contain $OH^-$.
    - Also, compounds like methane ($CH_4$) would be incorrectly labeled as an acid.

• Only pertains to reactants within aqueous solutions.

Practice

• Classify the following as an Arrhenius acid or an Arrhenius base:
    - $Ca(OH)_2$
    - $HNO_3$
    - $KOH$
    - $HBr$
    - $H_2SO_4$
    - $LiOH$

Bronsted-Lowry Theory

• Definition of Acids:
    - Any substance that can donate an $H^+$ to another substance.
      - Example:
        - In the reaction
          - $HCl + H_2O <br>ightarrow H_3O^+ + Cl^-$
          - $HCl$ is the Bronsted-Lowry acid because it donates its $H^+$ to $H_2O$.

• Definition of Bases:
    - Any substance that can accept an $H^+$.
      - Example:
        - In the same reaction, $H_2O$ is the Bronsted-Lowry base because it accepts the $H^+$ from $HCl$.

Conjugate Acids and Bases

• Conjugate Acid:
    - Forms after the base accepts the $H^+$ from the acid.

• Conjugate Base:
    - The particle that remains after the acid donates its $H^+$.

• Conjugate Acid-Base Pair:
    - Two substances that differ by only one $H$ atom.

• Example:
    - Reaction:
      $HCl + H_2O <br>ightarrow H_3O^+ + Cl^-$
      - $HCl$ is the acid.
      - $H_2O$ is the base.
      - $H_3O^+$ is the conjugate acid.
      - $Cl^-$ is the conjugate base.
      - $HCl$ and $Cl^-$ form a conjugate acid-base pair.
      - $H_2O$ and $H_3O^+$ form a conjugate acid-base pair.

Example of Base Reaction

• Example Reaction:
    - $NH_3 + H_2O <br>ightarrow OH^- + NH_4^+$
      - $NH_3$ is the base.
      - $H_2O$ is the acid.
      - $OH^-$ is the conjugate base.
      - $NH_4^+$ is the conjugate acid.

Amphoteric Substances

• Definition:
    - A substance that can act as both an acid and a base.

• Example:
    - Water can act as a base in one context and as an acid in another context.

Finding Conjugate Acids and Bases

• Given a Bronsted-Lowry acid, to find its conjugate base:
    - Take away one $H^+$ and lower (subtract) the charge by 1.

• Given a Bronsted-Lowry base, to find its conjugate acid:
    - Add one $H^+$ and raise (add to) the charge by 1.

Practice: Find Conjugate Bases of Given B-L Acids

• HI → __________

• HBr → __________

• $HCO_3^-$ → __________

• $H_2PO_4^-$ → __________

Practice: Find Conjugate Acids of Given B-L Bases

• $H_2PO_4^-$ → __________

• $F^-$ → __________

• $ClO_3^-$ → __________

• $CO_3^{2-}$ → __________

Acid Terminology

• Acids can be classified by how many $H^+$ they can donate:
    - Monoprotic Acid:
      - Can donate 1 hydrogen ion.
      - Example: $HNO_3$
    - Diprotic Acid:
      - Can donate 2 hydrogen ions.
      - Example: $H_2SO_4$
    - Triprotic Acid:
      - Can donate 3 hydrogen ions.
      - Example: $H_3PO_4$

Practice Identification of Acid, Base, Conjugate Acid, Conjugate Base

• For the reaction $HNO_3 + H_2O <br>ightarrow H_3O^+ + NO_3^-$
    - Identify:
      - Acid: $HNO_3$
      - Base: $H_2O$
      - Conjugate Acid: $H_3O^+$
      - Conjugate Base: $NO_3^-$

• Find the formula and name of the conjugate base of the following B-L acids:
    - $HCO_3^-$ → __________
    - $HI$ → __________

• Find the formula and name of the conjugate acid of the following B-L bases:
    - $ClO_3^-$ → __________
    - $H_2PO_4^-$ → __________

Daily Assignment

• Please return to Canvas and complete the Canvas Quiz Daily Assignment.