Acids, Bases and Salts class 10 Notes | Science Chapter 2 Class 10 Notes

The study of acids, bases, and salts forms another fundamental pillar in the Class 10 Chemistry curriculum, offering a deeper comprehension of the substances we interact with daily. Through the "Acids, Bases, and Salts Class 10 Notes," students will explore the unique characteristics of these chemical compounds, the processes that govern their interactions, and the vital role they play in both industrial applications and biological systems. These notes are carefully designed to guide students in understanding the nuances of pH levels, neutralization reactions, and the real-world significance of acids, bases, and salts, empowering them to confidently tackle related exam topics and expand their knowledge of these essential chemical compounds.

Acids, Bases, and Salts

1. Acids:

Acids are substances that produce hydrogen ions (H⁺) when dissolved in water. They turn blue litmus paper red and have a sour taste.
Example: HCl → H⁺ + Cl⁻.

2. Bases:

Bases are substances that produce hydroxide ions (OH⁻) when dissolved in water. They turn red litmus paper blue and have a bitter taste.
Example: NaOH → Na⁺ + OH⁻.

3. Indicators:

Indicators are substances used to identify acids and bases by showing a color change. Examples include litmus, phenolphthalein, and methyl orange.

Litmus: Red in acid, blue in base.
Phenolphthalein: Colorless in acid, pink in base.
Methyl orange: Red in acid, yellow in base.

4. Types of Acids and Bases:

a) Strong and Weak Acids:

Strong acids completely ionize in water.
Example: H₂SO₄ → 2H⁺ + SO₄²⁻.
Weak acids only partially ionize in water.
Example: CH₃COOH ⇌ CH₃COO⁻ + H⁺.

b) Strong and Weak Bases:

Strong bases completely dissociate in water.
Example: NaOH → Na⁺ + OH⁻.
Weak bases partially dissociate in water.
Example: NH₄OH ⇌ NH₄⁺ + OH⁻.

5. Neutralization Reaction:

A neutralization reaction occurs when an acid reacts with a base to form salt and water.
Example: HCl + NaOH → NaCl + H₂O.

6. pH Scale:

The pH scale measures the strength of acids and bases. It ranges from 0 to 14, where pH < 7 indicates acidity, pH = 7 is neutral, and pH > 7 indicates alkalinity.

Acidic solution: pH < 7.
Neutral solution: pH = 7.
Basic solution: pH > 7.

7. Salts:

Salts are formed when acids react with bases during neutralization. Salts can be neutral, acidic, or basic depending on the strength of the acid and base involved.
Example: HCl + NaOH → NaCl + H₂O.

8. Important Salts and Their Properties:

a) Common Salt (Sodium Chloride - NaCl):

Used in food and as raw material for chemical industries.
Example: NaCl is obtained by evaporation of seawater.

b) Baking Soda (Sodium Bicarbonate - NaHCO₃):

Used in baking, antacids, and fire extinguishers.
Preparation: NaCl + H₂O + CO₂ + NH₃ → NaHCO₃ + NH₄Cl.

c) Washing Soda (Sodium Carbonate - Na₂CO₃·10H₂O):

Used in cleaning agents and glass manufacturing.
Preparation: Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O.

d) Bleaching Powder (Calcium Oxychloride - CaOCl₂):

Used as a disinfectant and in the bleaching of clothes.
Preparation: Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O.

e) Plaster of Paris (Calcium Sulphate Hemihydrate - CaSO₄·½H₂O):

Used for setting fractured bones and making molds.
Preparation: 2CaSO₄·2H₂O (Gypsum) → CaSO₄·½H₂O (Plaster of Paris) + 1½H₂O.

9. Water of Crystallization:

Water of crystallization refers to the fixed number of water molecules present in one formula unit of a salt.
Example: CuSO₄·5H₂O (Copper sulphate pentahydrate) contains 5 water molecules.

10. Importance of pH in Everyday Life:

Plants and Animals: pH of soil affects plant growth.
Digestive System: Stomach produces HCl for digestion; antacids neutralize excess acid.
Tooth Decay: Tooth enamel erodes below pH 5.5 due to acid-producing bacteria.
Self-defense by Animals and Plants: Bee stings contain acid; baking soda (a mild base) can neutralize the sting.