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3.55: Acid-Base Neutralization

Difficulty Level: At Grade Created by: CK-12
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What is one of the most important characteristics of a referee? A referee must be neutral. He can’t favor one team over the other. In chemistry, being neutral means not being an acid or a base. Pure water is an example of a neutral substance. In some chemical reactions, an acid and a base combine to form neutral products, including water. You’ll see how this happens when you read this article.

Acids, Bases, and Ions

An acid is a compound that produces positive hydrogen ions (H+) and negative nonmetal ions when it dissolves in water. (Ions are atoms that have become charged by losing or gaining electrons.) Hydrochloric acid (HCl) is an example of an acid. When it dissolves in water, it produces positive hydrogen ions and negative chloride ions (Cl-). This can be represented by the chemical equation:

HCl \begin{align*}\mathrm{\overset{H_2O}{\rightarrow}}\end{align*} H+ + Cl-

A base is a compound that produces negative hydroxide ions (OH-) and positive metal ions when it dissolves in water. For example, when the base sodium hydroxide (NaOH) dissolves in water, it produces negative hydroxide ions and positive sodium ions (Na+). This can be represented by the chemical equation:

NaOH \begin{align*}\mathrm{\overset{H_2O}{\rightarrow}}\end{align*} OH- + Na+

Q: If you were to combine acid and base solutions, what products do you think would be produced?

A: Combining acid and base solutions produces water and a neutral ionic compound.

Reactions of Acids and Bases

When an acid and a base react, the reaction is called a neutralization reaction. That’s because the reaction produces neutral products. Water is always one product, and a salt is also produced. A salt is a neutral ionic compound.

Let’s see how a neutralization reaction produces both water and a salt, using as an example the reaction between solutions of hydrochloric acid and sodium hydroxide. The overall equation for this reaction is:

NaOH + HCl → H2O and NaCl

Now let’s break this reaction down into two parts to see how each product forms.

• Positive hydrogen ions from HCl and negative hydroxide ions from NaOH combine to form water. This part of the reaction can be represented by the equation:
H+ + OH- → H2O
• Positive sodium ions from NaOH and negative chloride ions from HCL combine to form the salt sodium chloride (NaCl), commonly called table salt. This part of the reaction can be represented by the equation:
Na+ + Cl- → NaCl

Another example of a neutralization reaction can be seen in the Figure below.

These antacid tablets contain the base calcium carbonate (CaCO3). The base reacts with hydrochloric acid (HCl) in the stomach. The reaction neutralizes the acid to relieve acid indigestion.

Q: What products are produced when antacid tablets react with hydrochloric acid in the stomach?

A: The products are water and the salt calcium chloride (CaCl2). Carbon dioxide (CO2) is also produced. The reaction is represented by the chemical equation:

CaCO3 + 2HCl → H2O + CaCl2 + CO2

Summary

• When acid and base solutions react, they produce water and a neutral ionic compound called a salt. The reaction is called a neutralization reaction.

Review

1. Describe a neutralization reaction.
2. What is a salt? Give an example.
3. Fill in the missing products in the chemical equation below. It represents a neutralization reaction between solutions of nitric acid (HNO3) and potassium hydroxide (KOH): HNO3 + KOH → ____ + _____

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Vocabulary Language: English

TermDefinition
neutralization reaction Reaction of an acid and a base that produces water and a salt, both of which are neutral in acidity.
salt Ionic compound formed when an acid and base react.

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