Neutralization Reactions

Neutralization Reactions: produce salt, water, and sometimes a gas when an acid and base react with and neutralize one another; typically exothermic.

Defining Acids and Bases:

We have three ways of defining acids and bases. A substance’s identity as an acid or base does not change based on which definition is used to describe it. These definitions are simply different ways of saying the same thing.

Acids and bases are electrolytes. Strong acids/bases are strong electrolytes and weak acids/bases are weak electrolytes.

Related Byte: Electrolytes and Strong Acid/Base List

Acids:

1. Arrhenius Definition: acids are substances that produce a hydrogen ion, H⁺, or a hydronium ion, H₃O⁺,  in an aqueous solution
2. Bronsted Definition: acids are substances that donate a proton in an aqueous solution (H⁺ is known as a proton).
3. Lewis: Definition: acids are substances that accept electrons in an aqueous solution.

Example:

Bases:

1. Arrhenius Definition: bases are substances that produce hydroxide ion, OH^–, in an aqueous solution.
2. Bronsted Definition: bases are substances that accept a proton in an aqueous solution  HINT: since bases contain a negative charge from their OH^– ion, they attract the  positive charge of the proton, H⁺!
3. Lewis Definition: bases are substances that donate electrons in an aqueous solution.

The equation below demonstrate how OH ions are produced, whether they are in the formula of the base or not:

Example:

NOTE: Ammonia, NH₃, is VERY commonly used weak that is often overlooked since it does not contain “OH.” However, note that by the Bronsted definition, a base should be able to produce OH ions, not necessarily contain them its formula!

The pH Scale in Brief:

Now that you’re familiar with acids and bases, let’s take a look at some acid/base neutralization reactions.

Acids, by their nature have a low pH and bases have a high pH, on the scale that determines acidity and basicity. Since the pH scale ranges from 0-14, the pH of 7 is deemed to be neutral.

http://commons.wikimedia.org/wiki/File:PH_scale_2.png

When the a “H” of an acid and the “OH” of a base react, they form water, which is neutral. Hence, the H and OH neutralize each other and the reason why acid-base reactions are called neutralization reactions.

The Basics of Neutralization Reactions:

1. Will react an acid and a base
2. The acid involved may be a pure acid (ie HCl) or an acidic salt (NaNH₄)
3. The base involved may be a pure base (ie NaOH) or basic salt (CaCO₃)
4. Will always produce a salt (ionic compound composed of a metal + nonmetal) and water
   1. Reactions involving CO₃^2- will also produce CO₂ gas
   2. Reactions involving SO₃^2- will also produce SO₂ gas
   3. Reactions involving NH₄OH will also produce NH₃ gas

Related Byte: Gas Producing Reactions

We can also write the molecular, complete ionic, and net ionic equations for acid-base neutralization reactions, just as did for precipitation reactions.

Reactions Producing Only Water:

Example:

Related Byte: Writing Molecular, Ionic, and Net Ionic Equations

Molecular:

Complete Ionic:

Net Ionic Equation:

This is the poster-child for acid-base reactions.

Reaction Producing Water and Gas (CO₂)

Example:

NOTE: immediate decomposes to form H₂O and CO₂ via the reaction below:

Molecular:

Complete Ionic:

Net Ionic: