Discover the complete concept of acids and bases, including definitions, theories, properties, real-life examples, and applications. Learn the differences between acids and bases with this easy-to-understand 2025 chemistry guide.
Acids and bases are fundamental chemical substances that play vital roles in various scientific, industrial, and biological processes. From the sour taste of lemon juice to the bitter feel of soap, acids and bases are all around us. Understanding their properties and behaviors is essential not only for chemistry students but also for professionals in healthcare, environmental science, agriculture, and manufacturing.
Table of Contents
What Are Acids and Bases?
Acids
Acids are substances that donate hydrogen ions (H⁺) or protons in a chemical reaction. They usually taste sour, have a pH less than 7, and turn blue litmus paper red.
Bases
Bases are substances that accept hydrogen ions or release hydroxide ions (OH⁻) in aqueous solutions. Bases often feel slippery to the touch, taste bitter, and turn red litmus paper blue.
Theories Defining Acids and Bases
Over the years, scientists have proposed several theories to define acids and bases more precisely. The three most widely accepted theories are:
1. Arrhenius Theory
- Acid: A substance that increases the concentration of H⁺ ions in aqueous solution.
- Base: A substance that increases the concentration of OH⁻ ions in aqueous solution.
Example:
- HCl → H⁺ + Cl⁻ (Acid)
- NaOH → Na⁺ + OH⁻ (Base)
Limitation: This theory is limited to aqueous solutions only.
2. Brønsted-Lowry Theory
- Acid: A proton (H⁺) donor.
- Base: A proton (H⁺) acceptor.
Example:
NH₃ + H₂O → NH₄⁺ + OH⁻
Here, NH₃ acts as a base by accepting a proton.
This theory expands acid-base reactions beyond just aqueous solutions.
3. Lewis Theory
- Acid: Electron pair acceptor.
- Base: Electron pair donor.
Example:
BF₃ (acid) + NH₃ (base) → F₃B←NH₃
This is the most inclusive theory and applies to a wide range of reactions.
Properties of Acids and Bases
Properties of Acids:
- Sour taste (e.g., citric acid in lemons)
- Conduct electricity (electrolytes)
- React with metals to produce hydrogen gas
- Neutralize bases to form salts and water
- pH value < 7
- Bitter taste (e.g., baking soda)
- Slippery feel (e.g., soap)
- React with acids to form salt and water
- Can conduct electricity in solution
- pH value > 7
Strong vs. Weak Acids and Bases
Strong Acids:
Properties of Bases:
Completely dissociate in water.
- Examples: HCl, HNO₃, H₂SO₄
Weak Acids:
Partially dissociate in water.
- Examples: Acetic acid (CH₃COOH), Citric acid
Strong Bases:
Completely dissociate in water.
- Examples: NaOH, KOH
Weak Bases:
Partially dissociate in water.
- Examples: Ammonia (NH₃), Magnesium hydroxide (Mg(OH)₂)
pH Scale: Measuring Acidity and Basicity
The pH scale ranges from 0 to 14 and indicates the concentration of hydrogen ions in a solution:
- 0–6: Acidic
- 7: Neutral (e.g., pure water)
- 8–14: Basic (alkaline)
Example:
- Lemon juice: pH 2
- Vinegar: pH 3
- Baking soda solution: pH 9
- Bleach: pH 12
Everyday Examples of Acids and Bases
Common Acids:
- Citric acid (found in citrus fruits)
- Acetic acid (in vinegar)
- Lactic acid (in sour milk)
- Carbonic acid (in carbonated drinks)
Common Bases:
- Sodium bicarbonate (baking soda)
- Ammonia (in household cleaners)
- Calcium hydroxide (in cement and lime water)
- Magnesium hydroxide (antacids)
Uses of Acids and Bases
Industrial Uses
Acids:
- Sulfuric acid is used in car batteries and fertilizers.
- Nitric acid is essential in making explosives and dyes.
- Hydrochloric acid is used in cleaning and leather processing.
Bases:
- Sodium hydroxide is key in soap and paper manufacturing.
- Calcium hydroxide is used in water treatment.
- Ammonium hydroxide is found in household cleaners.
Household Uses
- Vinegar (acetic acid) for cooking and cleaning.
- Baking soda (sodium bicarbonate) for cleaning and baking.
- Antacids (contain magnesium or calcium hydroxide) to relieve heartburn.
Importance in Biology and Environment
Biological Importance:
- Stomach produces hydrochloric acid to aid digestion.
- Buffer systems in the body help maintain a stable pH.
Environmental Role:
- Acid rain (caused by sulfuric and nitric acids) damages forests and aquatic life.
- Soil pH affects plant growth and nutrient availability.
- Ocean acidification from carbonic acid threatens marine ecosystems.
Safety and Handling
Acids and bases can be corrosive and dangerous. Always follow safety measures:
- Wear gloves and goggles when handling strong chemicals.
- Store in clearly labeled containers.
- Use proper ventilation when working with fumes.