Introduction

Acid-base reactions form a cornerstone of chemical processes, encompassing various types of reactions fundamental to both theoretical and practical chemistry. These reactions, often called neutralization reactions, occur when acids and bases interact to neutralize each other's chemical properties.

Types of Acid-Base Reactions

1. Neutralization Reactions

In the Arrhenius theory, neutralization occurs when hydrogen ions (H⁺) from acids combine with hydroxide ions (OH⁻) from bases. The general equation is:

$\text{Acid} + \text{Metal Hydroxide} \rightarrow \text{Salt} + \text{Water}$

For example, when hydrochloric acid reacts with sodium hydroxide:

$\text{HCl}_{(aq)} + \text{NaOH}_{(aq)} \rightarrow \text{NaCl}_{(aq)} + \text{H}_2\text{O}_{(l)}$

The net ionic equation simplifies to:

$\text{H}^+_{(aq)} + \text{OH}^-_{(aq)} \rightarrow \text{H}_2\text{O}_{(l)}$

2. Brønsted-Lowry Acid-Base Reactions

In the Brønsted-Lowry theory, acid-base reactions involve proton transfer. A key example is acid dissociation in water:

$\text{HCl}_{(aq)} + \text{H}_2\text{O}_{(l)} \rightarrow \text{Cl}^-_{(aq)} + \text{H}_3\text{O}^+_{(aq)}$

Acid-Metal Reactions

When acids react with metals, they produce salt and hydrogen gas:

$\text{Acid} + \text{Metal} \rightarrow \text{Salt} + \text{Hydrogen}$

The reactivity series determines the vigor of these reactions:

Metal	Reaction with Acid
K, Na	Extremely rapid, may ignite
Ca, Mg	Rapid bubbling
Al, Zn, Fe	Moderate to slow
Cu, Ag, Au	No reaction

Acid-Metal Oxide Reactions

Metal oxides react with acids to form salt and water:

$\text{Metal Oxide} + \text{Acid} \rightarrow \text{Salt} + \text{Water}$

For example:

$$\text{MgO}_{(s)} + 2\text{HCl}_{(aq)} \rightarrow \text{MgCl}_{2(aq)} + \text{H}_{2}\text{O}_{(l)}$$

Acid-Carbonate Reactions

Carbonates and hydrogen carbonates react with acids to produce salt, water, and carbon dioxide:

$\text{Acid} + \text{Carbonate} \rightarrow \text{Salt} + \text{Water} + \text{Carbon Dioxide}$

The reaction proceeds in steps:

Testing for Carbon Dioxide

Carbon dioxide can be identified using limewater (calcium hydroxide solution):

$$\text{Ca(OH)}_{2(aq)} + \text{CO}_{2(g)} \rightarrow \text{CaCO}_{3(s)} + \text{H}_{2}\text{O}_{(l)}$$

The formation of a white precipitate (CaCO₃) confirms the presence of CO₂.