ACIDS, BASES AND SALTS

Science

Chemistry deals with the study of matter and the changes it undergoes. Among the most important chemical substances that affect our daily life are acids, bases and salts. They play a crucial role in industries, agriculture, human digestion, medicine and environmental processes.

2. ACIDS

Definition:
An acid is a substance which produces hydrogen ions (H⁺) when dissolved in water.

Arrhenius Concept:
According to Arrhenius, acids are substances that release H⁺ ions in aqueous solution.
Example:
HCl → H⁺ + Cl⁻

Bronsted–Lowry Concept:
An acid is a proton donor.
Example:
HCl donates a proton to water.

Lewis Concept:
An acid is a substance that accepts an electron pair.
Example:
BF₃ acts as a Lewis acid.

Characteristics of Acids:
• Sour in taste
• Turn blue litmus red
• Conduct electricity in aqueous solution
• React with metals to produce hydrogen gas
• React with bases to form salt and water

Types of Acids:
(a) Based on Strength
Strong Acids:
Completely ionize in water.
Examples: HCl, HNO₃, H₂SO₄

Weak Acids:
Partially ionize in water.
Examples: Acetic acid, Carbonic acid

(b) Based on Origin
Organic Acids:
Present in living organisms.
Examples: Citric acid, Lactic acid, Acetic acid

Inorganic (Mineral) Acids:
Prepared from minerals.
Examples: HCl, H₂SO₄, HNO₃

3. BASES

Definition:
A base is a substance which produces hydroxide ions (OH⁻) in water.

Arrhenius Concept:
Bases release OH⁻ ions in aqueous solution.
Example:
NaOH → Na⁺ + OH⁻

Bronsted–Lowry Concept:
A base is a proton acceptor.

Lewis Concept:
A base is a substance that donates an electron pair.
Example:
NH₃

Characteristics of Bases:
• Bitter in taste
• Slippery or soapy to touch
• Turn red litmus blue
• Conduct electricity in aqueous solution
• Neutralize acids

Types of Bases:
Strong Bases:
NaOH, KOH

Weak Bases:
NH₄OH

Alkalis:
Bases that are soluble in water.
Examples: NaOH, KOH, Ca(OH)₂

4. SALTS

Definition:
Salts are formed when an acid reacts with a base. This reaction is called neutralization.

Neutralization Reaction:
Acid + Base → Salt + Water
Example:
HCl + NaOH → NaCl + H₂O

Nature of Salts:
Acidic Salt:
Formed from strong acid and weak base.
Example: NH₄Cl

Basic Salt:
Formed from weak acid and strong base.
Example: Na₂CO₃

Neutral Salt:
Formed from strong acid and strong base.
Example: NaCl

5. pH SCALE

Definition:
pH is a scale used to measure the acidity or basicity of a solution.

Range:
0 to 14

pH < 7 → Acidic
pH = 7 → Neutral
pH > 7 → Basic

Importance of pH:
• pH of stomach (1–2) helps digestion
• pH of blood is around 7.4
• Acid rain has pH less than 5.6
• Soil pH affects crop yield

6. INDICATORS

Indicators are substances that show different colours in acidic and basic solutions.

Natural Indicators:
• Litmus
• Turmeric
• China rose

Synthetic Indicators:
• Phenolphthalein
• Methyl orange

7. COMMON SALTS

(a) Washing Soda (Na₂CO₃·10H₂O)
Preparation:
From sodium chloride by Solvay process.

Properties:
• White crystalline solid
• Alkaline in nature

Uses:
• Cleaning agent
• Softening hard water
• Manufacture of glass and soap

(b) Baking Soda (NaHCO₃)
Preparation:
By reacting sodium chloride, ammonia and water.

Uses:
• Baking powder
• Antacid
• Fire extinguishers

Uses:
• Making moulds and casts
• Orthopaedic casts
• Decorative items

8. ROLE IN DAILY LIFE
• Acids in digestion (HCl)
• Bases in cleaning agents
• Salts in food preservation
• pH control in agriculture and environment

CONCLUSION
Acids, bases and salts are essential chemical substances that influence both natural processes and human life. Understanding their properties and applications is vital for science and society.

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Subject: Science

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