R3.1.7 Neutralization reactions

Neutralization Reactions: Acids and Bases React to Form Salts and Water

You’ve just eaten a spicy meal, and a burning sensation in your chest leaves you reaching for an antacid tablet.
Within minutes, you feel relief. What’s happening in your stomach?
The excess hydrochloric acid ( $HCl$ ) in your stomach reacts with the weak base in the antacid to form a salt and water.

This process, called neutralization, is one of the most fundamental reactions in chemistry.

What Is Neutralization?

Definition

Neutralization

Neutralization is a chemical reaction where an acid reacts with a base to produce a salt and water.

During this reaction, acidic hydrogen ions ( $H^{+}$ ) combine with basic hydroxide ions ( ${OH}^{-}$ ) to form water ( $H_{2} O$ ).

General Equation for Neutralization:

$Acid + Base \to Salt + Water$

Hint

This reaction is typically exothermic, meaning it releases heat. The specific salt formed depends on the acid and base involved.

Analogy

Think of neutralization as a chemical “truce” between acids and bases. Just as two opposing forces might come together to create balance, acids and bases react to form stable products—salt and water.

Exploring Neutralization Through Examples

Let’s break down two common types of neutralization reactions: acids reacting with metal oxides and acids reacting with hydroxide bases.

1.Acid + Metal Oxide

Metal oxides are basic in nature.
When an acid reacts with a metal oxide, the products are a salt and water.

Example

$2HCl (aq) + MgO (s) \to {MgCl}_{2} (aq) + H_{2} O (l)$

Step-by-Step Breakdown:

Reactants: Hydrochloric acid $HCl$ provides $H^{+}$ ions, and magnesium oxide $MgO$ provides $O^{2 -}$ ions.
Reaction: The $H^{+}$ ions combine with $O^{2 -}$ ions to form water $H_{2} O$ , while the ${Mg}^{2 +}$ ions from the oxide pair with ${Cl}^{-}$ ions to form magnesium chloride ${MgCl}_{2}$ .
Products: Salt ${MgCl}_{2}$ and water $H_{2} O$ are formed.

2.Acid + Base

When an acid reacts with a base (commonly a hydroxide), the products are also a salt and water.

Example

$HCl (aq) + NaOH (aq) \to NaCl (aq) + H_{2} O (l)$

Step-by-Step Breakdown:

Reactants: Hydrochloric acid $HCl$ ) provides $H^{+}$ ions, and sodium hydroxide $NaOH$ provides ${OH}^{-}$ ions.
Reaction: The $H^{+}$ ions combine with ${OH}^{-}$ ions to form water $H_{2} O$ , while the ${Na}^{+}$ ions from the base pair with ${Cl}^{-}$ ions to form sodium chloride $NaCl$ .
Products: Salt $NaCl$ and water $H_{2} O$ are formed.

Common Mistake

Students often forget to balance the equation. Always verify that the number of atoms on both sides of the equation is equal.

3.Acid + Metal Carbonate

Metal carbonates react with acids to produce a salt, water, and carbon dioxide gas.
This reaction is often observed with effervescence due to the release of carbon dioxide.

Example

$2 H C l (a q) + C a C O_{3} (s) \to C a C l_{2} (a q) + H_{2} O (l) + C O_{2} (g)$

Step-by-Step Breakdown:

Reactants: Hydrochloric acid $H C l$ provides $H^{+}$ ions, while calcium carbonate $C a C O_{3}$ supplies $C a^{2 +}$ and $C O_{3}^{2 -}$ ions.
Reaction: The $H^{+}$ ions from the acid react with $C O_{3}^{2 -}$ ions, forming $H_{2} O$ and $C O_{2}$ . The $C a^{2 +}$ ions pair with $C l^{-}$ ions to form the salt calcium chloride $C a C l_{2}$ .
Products: A salt $C a C l_{2}$ , water $H_{2} O$ , and carbon dioxide $C O_{2}$ are formed. The release of carbon dioxide gas often results in bubbling (effervescence).

4.Acid + Metal Hydrogen Carbonate

Metal hydrogen carbonates react with acids similarly, producing a salt, water, and carbon dioxide gas.

Example

$H C l (a q) + N a H C O_{3} (s) \to N a C l (a q) + H_{2} O (l) + C O_{2} (g)$

Step-by-Step Breakdown:

Reactants: Hydrochloric acid $H C l$ provides $H^{+}$ ions, while sodium hydrogen carbonate $N a H C O_{3}$ supplies $N a^{+}$ and $H C O_{3}^{-}$ ions.
Reaction: The $H^{+}$ ions react with the hydrogen carbonate ion $H C O_{3}^{-}$ , breaking it down into $H_{2} O$ and $C O_{2}$ . The sodium ion $N a^{+}$ pairs with the chloride ion $C l^{-}$ to form sodium chloride.
Products: A salt $N a C l$ , water $H_{2} O$ , and carbon dioxide $C O_{2}$ gas are formed, often observed with effervescence.

Tip

During titration experiments, neutralization reactions help determine the concentration of unknown acids or bases by reacting them with a standard solution of known concentration.

Reflection and Connections

Self review

Write the balanced molecular equation for the reaction between sulfuric acid $H_{2} {SO}_{4}$ and potassium hydroxide $KOH$ .
Predict the products when nitric acid ${HNO}_{3}$ reacts with calcium oxide $CaO$ .
A solution of sodium hydroxide is added to hydrochloric acid until neutralization occurs. Write the ionic equation for this reaction.

Theory of Knowledge

How might the concept of neutralization relate to broader ideas of balance and equilibrium in other disciplines, such as biology or economics?
Can you think of examples where restoring balance is critical?

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R3.1.7 Neutralization reactions

Neutralization Reactions: Acids and Bases React to Form Salts and Water

What Is Neutralization?

General Equation for Neutralization:

Exploring Neutralization Through Examples

1.Acid + Metal Oxide

2.Acid + Base

3.Acid + Metal Carbonate

4.Acid + Metal Hydrogen Carbonate

Reflection and Connections

You've read 2/2 free chapters this week.

Introduction to Neutralization Reactions

Example: