Acids, Bases & pH

Acids, Bases, and pH Overview

Introduction

• Subject: Biology 189: Fundamentals for Life Sciences

• Instructor: Earl Yoon

Learning Objectives

• Explain water ionization and its significance for pH.

• Describe the effects of acids and bases on [H+] and [OH-] concentrations, and on pH.

• Apply the pH formula to determine concentrations and pH of solutions.

• Understand the pH scale and its relation to [H+].

• Understand the importance of buffers in maintaining pH.

Water Ionization

• Ionization Process: Covalent bonds in water can break, leading to the formation of hydroxide ions (OH-) and hydrogen ions (H+).

• The ionization represents the balance of these ions in solution.

Measurement of Water Ionization

• Concentrations:

  • [H+] in pure water: 1x10^-7 M

  • [OH-] in pure water: also 1x10^-7 M

• Product of concentrations: [H+] x [OH-] = 1 x 10^-14 M

• The relationship is crucial for understanding acid and base behavior.

Acids

• Definition: Acids are substances that donate H+ ions (protons) to a solution.

• Effects on Solution:

  • Increases [H+]

  • Decreases [OH-]

• Examples:

  • Hydrochloric acid (HCl): H+ + Cl-

  • Sulfuric acid (H2SO4): H+ + HSO4-

• Taste: Sour

Bases

• Definition: Bases are H+ acceptors and typically release OH- ions in solution.

• Effects on Solution:

  • Decreases [H+]

  • Increases [OH-]

• Examples:

  • Sodium Hydroxide (NaOH): Na+ + OH-

  • Ammonia (NH3): accepts H+ to form NH4+

Acids vs. Bases

• Understanding the acidity and basicity of solutions:

  • Acidic solutions have higher [H+] and lower [OH-].

  • Basic solutions have lower [H+] and higher [OH-].

  • Neutral solutions: [H+] = [OH-]

pH Scale

• Definition of pH:

  • pH measures the concentration of hydrogen ions ([H+]) in solution.

  • pH = -log[H+]

• Example Calculation:

  • For pure water:

    • [H+] = 1x10^-7 M,

    • pH = -log[1x10^-7] = 7

• pH describes a scale from 0 (acidic) to 14 (basic), with 7 being neutral.

Calculating pH

• Acidic Solutions:

  • Higher [H+], for example, [H+] = 1x10^-4 M; pH = 4.

• Basic Solutions:

  • Lower [H+], for example, [OH-] = 1x10^-3 M, leading to [H+] = 1x10^-11 M; pH = 11.

Importance of pH

• Cellular Functions: pH levels are crucial for the proper functioning of cells and their components.

Buffers

• Definition: Buffers help maintain pH levels by absorbing or releasing H+ ions.

• How Buffers Work:

  • Accept H+ when pH drops (too acidic).

  • Donate H+ when pH rises (too basic).

• Common Example: Carbonic acid and bicarbonate in blood regulate pH ( CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-).

Blood pH Regulation

• Ideal pH Range: 7.35 - 7.45

• Processes that affect blood pH and the role of buffers in maintaining homeostasis.

In-Class Questions and Review

• Examples provided for calculating pH and determining acid-base characteristics of solutions.

Vocabulary

• Proton/Hydrogen ion

• Hydroxide ion

• Hydronium ion

• pH

• Buffer

• Salt