L1 - The Brønsted-Lowry Theory

The concept of acids you currently work with involves a reaction with water to produce hydronium ions. As you know from earlier in this module, bases dissociate to produce hydroxide ions. Those descriptions work well for substances like hydrochloric acid (strong acid) and calcium hydroxide (strong base) where there is 100% dissociation. The following reaction illustrates our previous observations:

But if HCO₃^-(aq) is added to a stonger base, it makes the solution less basic.  Therefore we must conclude that something must be reacting to decrease the concentration of hydroxide ions.

A similar unusual behavior happens when ammonia is mixed with water.  When the reaction happens, ammonium is produced which acts more like an acid, despite starting as a base.  So then, how do you explain the acidic properties of the ammonium ion and the basic properties of the carbonate ion?

Ammonium is commonly used in nitrogen-based fertilizers, and carbonate is one of many chemical components in soil—especially soils in Alberta. What is necessary to better understand the acidic and basic properties of these substances? Would this understanding help you to predict changes that might occur to soil as a result of soil management?

Consider the following questions as you complete this lesson:

• What occurs during a chemical reaction between an acid and a base?
• How does the Brønsted-Lowry theory support what is known about the equilibrium of aqueous acids and bases?
• How do conjugate acid-base pairs form an equilibrium system?