Acids, Bases, and Salts: Class 10 science chapter 2 notes
Introduction
Acids, bases, and salts are fundamental concepts in chemistry that play a pivotal role in our daily lives, nature, and various industries. Recognizing their characteristics and reactions not only builds a strong foundation in chemistry for students but also enhances practical understanding for real-world applications. (class 10 science chapter 2 notes)
1. Acids
Definition and Characteristics
- Acids are chemical substances recognized by their sour flavor and their tendency to change blue litmus paper to red.
- Common examples include hydrochloric acid, sulphuric acid, and acetic acid, which occurs naturally in vinegar.
- Natural sources: Citrus fruits (like lemons, oranges), curd, and tamarind contain natural acids.
Chemical Properties
- Reaction with Metals: Produces salt and hydrogen gas.
- Example: Zn + H₂SO₄ → ZnSO₄ + H₂
- Reaction with Metal Carbonates and Bicarbonates: This reaction leads to the creation of a salt, the release of carbon dioxide gas, and the formation of water.
- Example: Calcium carbonate reacts with hydrochloric acid to yield calcium chloride, carbon dioxide, and water.
(CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O)
- Example: Calcium carbonate reacts with hydrochloric acid to yield calcium chloride, carbon dioxide, and water.
- Reaction with Metal Oxides: Produces salt and water.
Tests for Acids
- Release of H₂ gas (tested with burning splint producing a ‘pop’ sound) when reacted with metals.
class 10 science chapter 2 notes
2. Bases
Definition and Characteristics
- Bases are substances known for their sharp, bitter flavor, slippery feel on the skin, and their ability to turn red litmus paper into blue.
- Common examples: Sodium hydroxide, potassium hydroxide, and calcium hydroxide.
Chemical Properties
- Reaction with Zinc and Aluminium: Releases hydrogen gas.
- Reaction with Acids: Produces salt and water (neutralization reaction).
Tests for Bases
- Bases taste bitter, feel soapy, change red litmus to blue, and produce hydroxide ions in water-based solutions.
3. Common Properties of Acids and Bases
- Both acids and bases are electrolytes and conduct electricity in aqueous solutions due to the presence of ions (H⁺ for acids, OH⁻ for bases).
- The interaction of an acid with a base gives rise to a neutralization process where salt and water are produced as end products.
4. Indicators and pH Scale
Indicators
- Substances that change color to indicate the presence of an acid or base.
- Natural indicators: Litmus (red in acid, blue in base), turmeric, china rose.
- Synthetic indicators: Methyl orange, phenolphthalein.
pH Scale
- The pH value shows how acidic or basic a solution is, measured from 0 to 14. Substances below 7 are acidic, above 7 are basic, and a pH of 7 represents a neutral solution such as distilled water.
- “pH” stands for the power of hydrogen ion concentration in a solution.
5. Importance of pH in Everyday Life
- Plants and Animals: Survival depends on maintaining a specific pH range. Soil pH affects crop growth.
- Digestive System: The stomach produces HCl to aid digestion; antacids neutralize excess acid.
- Tooth Decay: Caused by acids produced by bacteria below pH 5.5.
- Environment: Rain with pH below 5.6 is considered acid rain and is harmful to plants and aquatic life.
6. Salts
Types and Properties
- Formed by the neutralization reaction between an acid and a base.
- Examples: Sodium chloride (common salt), sodium carbonate (washing soda), sodium hydrogen carbonate (baking soda), calcium sulphate (Plaster of Paris).
Common Salts
| Name | Chemical Formula | Common Uses |
|---|---|---|
| Sodium Chloride | NaCl | Cooking, food preservation |
| Sodium Hydroxide | NaOH | Soap, detergent, paper, textiles |
| Sodium Bicarbonate | NaHCO₃ | Baking soda, antacids |
| Washing Soda | Na₂CO₃·10H₂O | Water softening, cleaning |
| Bleaching Powder | Ca(OCl)₂ | Disinfectant, bleaching agent |
| Plaster of Paris | CaSO₄·½H₂O | Construction, casts in medicine |
Preparation and Uses
- Sodium Chloride: Obtained from seawater and rock salt.
- Baking Soda: Under specific conditions, baking soda is synthesized using common salt and carbon dioxide gas.
- Bleaching Powder: Made by passing chlorine over dry slaked lime.
- Plaster of Paris: Formed by heating gypsum.
7. Water of Crystallisation
- Certain salts contain water molecules as part of their crystal structure (hydrated salts).
- Example: Copper sulphate (CuSO₄·5H₂O) and gypsum (CaSO₄·2H₂O).
- When hydrated salts are heated, they lose water and become anhydrous, often changing color in the process.
class 10 science chapter 2 notes
8. Everyday Applications
- Neutralization is vital in antacids (soothing excess stomach acid), treating soil acidity, and industrial processes.
- pH measurements ensure suitable conditions in water treatment, agriculture, and healthcare.
Conclusion
These principles are the foundation of chemistry and have a significant effect on the environment as well as modern advancements in science and industry.