Bases: Properties & Reactions

Definition

Bases are chemical substances that can accept protons (H⁺) or donate hydroxide ions (OH^–) in a chemical reaction. They have a characteristic bitter taste (though tasting chemicals in a lab is highly discouraged!) and a slippery feel. Bases are the chemical opposite of acids.

Explanation

Bases are compounds that increase the concentration of hydroxide ions (OH^–) in a solution. Strong bases completely dissociate in water, while weak bases only partially dissociate. The strength of a base is determined by its ability to release hydroxide ions or accept protons. They can neutralize acids, forming salts and water. The pH scale is used to measure the acidity or basicity of a solution, with bases having a pH greater than 7.

Core Principles and Formulae

Key Concepts:

Hydroxide Ions (OH^–): The defining characteristic of a base in the Arrhenius definition.
Proton Acceptors: In the Bronsted-Lowry definition, bases accept protons (H⁺).
pH Scale: Measures the acidity or basicity of a solution. Bases have pH values greater than 7.
Neutralization: The reaction between an acid and a base, typically forming a salt and water.

Important Formulae:

pH + pOH = 14 (at 25°C), where pOH is the measure of hydroxide ion concentration.
pH = -log₁₀[H⁺], where [H⁺] is the concentration of hydrogen ions.
pOH = -log₁₀[OH^–], where [OH^–] is the concentration of hydroxide ions.

Reaction of Bases with Metals

Some bases react with certain metals, particularly those that are amphoteric (can react with both acids and bases), such as aluminum (Al) and zinc (Zn). These reactions produce hydrogen gas (H₂) and a complex salt.

Example: The reaction of sodium hydroxide (NaOH) with aluminum (Al):

6NaOH(aq) + 2Al(s) → 2Na₃AlO₃(aq) + 3H₂(g)

2NaOH(aq) + 2Al(s) + 6H₂O(l) → 2NaAl(OH)₄(aq) + 3H₂(g)

Reaction of Bases with Non-Metal Oxides

Bases react with non-metal oxides to form salts and water. Non-metal oxides are acidic oxides. This reaction is essentially a neutralization reaction.

Example: The reaction of sodium hydroxide (NaOH) with carbon dioxide (CO₂):

2NaOH(aq) + CO₂(g) → Na₂CO₃(aq) + H₂O(l)

Examples

Common examples of bases include:

Sodium Hydroxide (NaOH) – also known as lye or caustic soda.
Potassium Hydroxide (KOH)
Ammonia (NH₃)
Calcium Hydroxide (Ca(OH)₂) – also known as slaked lime.
Magnesium Hydroxide (Mg(OH)₂) – found in milk of magnesia.

Common Misconceptions

Misconception: All substances with a bitter taste are bases.

Correction: While bases often have a bitter taste, it’s dangerous to taste chemicals in the lab. Furthermore, some other substances might have a bitter taste for various reasons.

Misconception: All bases are strong and highly corrosive.

Correction: Bases vary in strength. Some, like sodium hydroxide (NaOH), are strong, while others, like ammonia (NH₃), are weak.

Importance in Real Life

Bases have numerous applications in everyday life and industry:

Cleaning Products: Many household cleaners contain bases, such as ammonia, to remove grease and grime.
Soap Making: Bases (like NaOH or KOH) are essential for saponification, the process of making soap.
Agriculture: Lime (calcium hydroxide) is used to neutralize acidic soils.
Antacids: Magnesium hydroxide and other bases are used to treat heartburn by neutralizing stomach acid.
Industrial Processes: Bases are used in various industrial processes, such as paper manufacturing and the production of textiles.

Fun Fact

The term “alkali” is often used interchangeably with “base,” especially when referring to water-soluble bases. The word “alkali” comes from the Arabic word “al-qili,” meaning “ashes,” referring to the source of the first known bases (obtained from burning plants).

History or Discovery

The understanding of acids and bases has evolved over time.

Early Concepts: The ancient Egyptians and Greeks knew about acids and bases, but they didn’t understand the underlying chemistry. They used bases like ashes (containing potassium carbonate) for cleaning.

Arrhenius Theory (1884): Svante Arrhenius defined bases as substances that produce hydroxide ions (OH^–) in water.

Bronsted-Lowry Theory (1923): Johannes Nicolaus Brønsted and Thomas Martin Lowry broadened the definition, defining bases as proton (H⁺) acceptors.

FAQs

Q: What is the difference between a strong base and a weak base?

A: A strong base completely dissociates in water, releasing a high concentration of hydroxide ions. A weak base only partially dissociates, releasing fewer hydroxide ions.

Q: How are bases used in soaps?

A: Bases like sodium hydroxide (NaOH) or potassium hydroxide (KOH) react with fats and oils in a process called saponification, forming soap and glycerol.

Q: Are all bases corrosive?

A: Not all bases are corrosive, but many strong bases can be very corrosive, meaning they can damage or destroy other substances they come into contact with.