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