Lecture on Acids and Bases

Introduction

• This lecture provides a series of multiple-choice questions on acids and bases.
• It is recommended to attempt solving these problems before looking at the solutions.

Strong Acids and Bases

• Strong Acids: HI, HBr, HCl, H2SO4, HClO4, and HNO3.
• Strong Bases: Example includes sodium hydroxide.
• Question 1: Identify strong acids from a list. Correct answer: Perchloric acid.

Calculating pH

• Formula: pH = -log[H3O+].
• Question 2: Given [H3O+] = 4.7 x 10^-3, estimate pH (between 2 and 3).
• Question 3: Calculate pOH knowing pH, using pH + pOH = 14.

Bronsted-Lowry Acids and Bases

• Concepts:
  • Acid: proton donor.
  • Base: proton acceptor.
• Question 4: Identify the Bronsted-Lowry base in a reaction. Answer: Water.
• Conjugate Acids/Bases: Add/remove hydrogen to form conjugates.

Ion Concentrations

• Autoionization of Water:
  • Kw = [H3O+][OH-] = 1 x 10^-14 at 25°C.
• Question 5: Calculate [H3O+] given [OH-].

Additional pH and Ion Concentration Calculations

• Question 6: Given pH, find [H3O+]. Use [H3O+] = 10^(-pH).
• Question 7: Determine if a solution is acidic, basic, or neutral based on pH.

Strength of Acids/Bases

• Ka and Kb Values: Higher values indicate stronger acids/bases.
• Question 10: Compare HF and HCN using Ka values to determine stronger acid.

Calculations with Molarity

• Question 11: pH of a 0.025 M HCl solution.
• Question 12: pH of 0.75 M hypochlorous acid solution given Ka.

Trends in Acid Strength

• Periodic Table Trends:
  • Acid strength increases going down a group and across a period.
  • Larger conjugate base ions stabilize better, making the acid stronger.

Salts and pH

• Amphoteric Substances: Act as both acids and bases (e.g., water).
• Question 22: Determine which salts create basic solutions. Correct answer: Sodium nitrite.

Relationships between pKa, Ka, and Acid Strength

• pKa and Acid Strength: As pKa decreases, acid strength increases.

Practical Applications

• Problem-solving: Thorough examples and step-by-step problem-solving methods using equilibrium expressions, ICE tables, and calculating dissociation percentages to understand acid-base behaviors in various scenarios.

Summary

• Methodology to solve problems related to pH, ion concentrations, acid/base strength, and reactivity.
• Understanding of how to use equilibrium constants (Ka, Kb) and concepts of conjugate acids/bases in predicting and analyzing chemical behavior.