Lecture Notes: Basics of Acids and Bases

Identifying Acids and Bases

• Acids: Typically have a hydrogen (H) in front (e.g., HCl, HF, HC2H3OH).
• Bases: Typically have a hydroxide ion (OH-), e.g., NaOH, KOH.
• Charge: Hydrogen with a positive charge is an acid; with a negative charge, it's a base.

Definitions

Arrhenius Definition

• Acids: Release H+ ions into solution, equivalent to hydronium ions (H3O+) in water.
• Bases: Release OH- ions into solution.

Bronsted-Lowry Definition

• Acids: Proton donors.
• Bases: Proton acceptors.
• Example: HCl in water, HCl donates a proton becoming Cl-; water accepts a proton becoming H3O+.

Conjugate Acids and Bases

• Conjugate Acid: Formed when a base gains a hydrogen ion.
• Conjugate Base: Formed when an acid loses a hydrogen ion.
• Example: NH3 (base) becomes NH4+ (conjugate acid); H2O (acid) becomes OH- (conjugate base).

The pH Scale

• Range: Typically 0-14.
• Neutral: pH of 7.
• Acidic: pH < 7.
• Basic: pH > 7.
• Calculation:
  • pH = -log[H3O+]
  • pOH = -log[OH-]
  • pH + pOH = 14 at 25°C.

Strong vs Weak Acids and Bases

Strong Acids

• Ionize completely; strong electrolytes.
• Common examples: HCl, HBr, H2SO4.

Weak Acids

• Partially ionize; weak electrolytes.
• Examples: Acetic acid, HF.

Strong Bases

• Soluble ionic compounds; ionize completely.
• Examples: NaOH, KOH.

Weak Bases

• Insoluble compounds; do not ionize completely.
• Examples: Ammonia, acetate.

Chemical Reactions

• Strong Acids: Single arrow indicates complete ionization.
• Weak Acids: Double arrow indicates equilibrium.

Properties of Acids and Bases

• Acids: Taste sour, turn blue litmus paper red.
• Bases: Taste bitter, feel slippery, turn red litmus paper blue.

Definitions Recap

• Arrhenius: Acids release H+, Bases release OH-.
• Bronsted-Lowry: Acids donate protons, Bases accept protons.
• Lewis: Acids accept electron pairs, Bases donate electron pairs.

Additional Concepts

• Amphoteric Substances: Can act as either acid or base (e.g., water, H2PO4-).
• Kw (Autoionization constant of water): [H3O+][OH-] = 1 x 10^-14 at 25°C.
• Relation of Ka and Kb: Ka x Kb = Kw.
• Impact of Temperature: Affects the equilibrium constants like Kw.

Problem-Solving and Calculations

• Practice problems involve calculating pH, pOH, and concentrations using given formulas.
• Understanding the relationship between acid/base strength and their constants (Ka, Kb).

Exercises

• Match terms with definitions and apply concepts to reaction examples.
• Identification of strong/weak acids/bases and their conjugates based on given examples and Ka/Kb values.

Conclusion

• Key Takeaway: Strong acids have high Ka and low pKa, whereas strong bases have high Kb values.