Acids and Bases: Properties, Definitions, and Reactions

Acid/Base Properties

Defining Acids and Bases

Over the years, chemists have developed several theories to define acids and bases, each providing a deeper understanding of their behavior in chemical reactions. The three main definitions are:

• Arrhenius Theory: Defines acids as substances that produce hydrogen ions (H+) in aqueous solution, and bases as substances that produce hydroxide ions (OH-).

• Brønsted-Lowry Theory: Defines acids as proton donors and bases as proton acceptors.

• Lewis Theory: Defines acids as electron pair acceptors and bases as electron pair donors.

Soluble bases are also known as alkalis.

Examples of Acids

Common Acids and Their Everyday Uses

Acids are found in many everyday substances and have a variety of practical applications. Below is a table summarizing common acids, their formulas, and uses:

Name	Formula	Uses
Hydrochloric acid	HCl	Present in stomach acid, helps digest proteins
Sulfuric acid	H2SO4	Used in car batteries, fertilizers, and detergents
Nitric acid	HNO3	Used in the manufacture of explosives
Ethanoic acid (acetic acid)	CH3COOH	Found in vinegar, used in food preservation
Carbonic acid	H2CO3	Found in carbonated soft drinks
Citric acid	H3C6O7	Found in the juice of citrus fruits

Examples of Bases

Common Bases and Their Uses

Bases are also widely used in daily life and industry. The following table lists common bases, their formulas, and uses:

Name	Formula	Uses
Sodium hydroxide	NaOH	Used in drain and oven cleaners, soap making
Ammonia	NH3	Used in household cleaners, manufacture of explosives
Calcium hydroxide	Ca(OH)2	Found in cement and mortar, used to adjust soil pH

Properties of Acids and Bases

Physical and Chemical Properties

Acids and bases have distinct properties that can be used to identify them in the laboratory and in everyday life.

Properties of Acids	Properties of Bases
Turn litmus indicator red	Turn litmus indicator blue
Are corrosive	Are caustic and feel slippery
Taste sour	Taste bitter
React with bases	React with acids
Solutions have a pH of less than 7	Solutions have a pH of greater than 7
Solutions conduct an electric current	Solutions conduct an electric current

pH Scale

Measuring Acidity and Alkalinity

The pH scale is a measure of how acidic or alkaline a solution is, based on the concentration of hydrogen ions (H+) in the solution. The scale ranges from 0 to 14:

• pH = 7: Neutral solution (e.g., pure water)

• pH < 7: Acidic solution

• pH > 7: Alkaline (basic) solution

The pH is mathematically defined as:

$\text{pH} = -\log_{10}[\text{H}^+]$

Indicators such as litmus paper and universal indicator are used to determine the pH of a solution. Litmus turns red in acids and blue in bases, while universal indicator shows a range of colors depending on the pH.

Additional info:

• Organic acids such as ethanoic acid (acetic acid) and citric acid are important in biological and food chemistry.

• Understanding acid-base properties is foundational for organic reaction mechanisms, buffer systems, and analytical chemistry.