Brønsted-Lowry Acids and Bases

Introduction

• Johannes Brønsted and Thomas Lowry (1923) definition: 
  • Focused on the reactions that take place between acids and bases. 
  • Brønsted-Lowry Acid: a compound that donates a proton to another compound. 
  • Brønsted-Lowry Base: a compound that accepts a proton from another compound. 

What Types of Compounds are Acids vs Bases?

• Acids:

  1. Molecules: Both organic and inorganic 
  2. Cations that contain H
  3. Anions that contain H

• Bases: 

  1. Ionic compounds that contain OH-  NaOH,  Ca(OH)2
  2. Molecules -  Primarily amines   ( contain a C-NH2 bond)
  3. Anions – With and without H     (  F-.   CO32-) 

Brønsted-Lowry Acid/Base Theory

• Conjugate base: the species formed when a proton is removed from an acid  
• Conjugate acid: the species formed when a proton is added to a base

Amphiprotic Species

• Amphiprotic: a species that can either accept or donate a proton
• An amphiprotic species can serve as an acid or a base. 
  • Example: Water   
  • In the presence of an acid, water acts as a base.
  • In the presence of a base, water acts like an acid.
• Anions with a removable H+ are amphiprotic.
• HCO3-for example, could gain or lose an H+

Water

• Acid ionization: the reaction between a Brønsted-Lowry Acid and water
• Base ionization: the reaction between a Brønsted-Lowry Base and water
• In pure water, water also acts both as an acid and a base. 
• Autoionization of water:
  • Ion product constant for water, Kw: the equilibrium constant for the autoionization of water
  • At 25 °C, Kw = 1.0 × 10–14