CBSE Acid Base and Salt Class 10 Notes: Complete Guide Here

Acid Base and Salt Class 10 Notes

1. Acids

Chemical Definition:
An acid is a substance that produces hydrogen ions (H⁺) as the only positive ions in an aqueous solution.

Physical Properties:

• Taste: Sour (khatta)

• Corrosive in nature

Indicator Behaviour:

• Turns blue litmus paper red

Common Examples:

2. Bases

Chemical Definition:
A base is a substance that increases the concentration of hydroxyl ions (OH⁻) in an aqueous solution.

Physical Properties:

• Taste: Bitter (kadwa)

• Feel: Soapy or slippery to touch

Indicator Behaviour:

• Turns red litmus paper blue

Alkalis:
Bases soluble in water are called alkalis, such as NaOH and KOH.

Common Examples:

3. Indicators

Indicators are substances used to detect whether a solution is acidic or basic.

Common Indicators:

Olfactory Indicators

These are substances whose smell changes depending on the medium. They are particularly useful for visually impaired students.

• Retain smell in acidic solution

• Lose smell in the basic solution
  Examples: Onion, Vanilla essence, Clove oil

 Acids and Bases in Water

Hydronium Formation:

• Acids produce H⁺ ions in water, which combine with water molecules to form hydronium ions (H₃O⁺).

• Example: HCl + H₂O → H₃O⁺ + Cl⁻

Bases in Water:

• Bases increase OH⁻ ions in water. Water-soluble bases like NaOH and KOH are called alkalis.

Dilution of Acid:

• Adding concentrated acid to water is highly exothermic.

• Always add acid to water slowly with stirring to prevent splashing.

Electrical Conductivity:

• Aqueous solutions of acids and bases conduct electricity due to free ions.

• Substances like glucose and alcohol do not ionize and hence do not conduct electricity.

Important Reactions

a) Reaction with Metals:

• Acids react with active metals to produce salt and hydrogen gas.

  • Example: Zn + H₂SO₄ → ZnSO₄ + H₂↑

• Some bases (like NaOH) also react with metals:

  • 2NaOH + Zn → Na₂ZnO₂ + H₂↑

b) Reaction with Carbonates and Hydrogen Carbonates:

• Acid + Metal Carbonate → Salt + H₂O + CO₂

• Acid + Metal Hydrogen Carbonate → Salt + H₂O + CO₂

• Test: CO₂ turns limewater milky due to CaCO₃ formation.

c) Neutralization Reaction:

• Acid + Base → Salt + Water

• Example: HCl + NaOH → NaCl + H₂O

d) Reactions of Oxides:

• Metal oxides are generally basic and react with acids to form salt and water.

• Non-metal oxides are generally acidic and react with bases to form salt and water.

Strength of Acids and Bases

• Strong acids (e.g., HCl, H₂SO₄) release high concentration of H⁺ ions.

• Weak acids (e.g., CH₃COOH) release low concentration of H⁺ ions.

• Strong bases (e.g., NaOH, KOH) release high OH⁻ ions.

• Weak bases (e.g., NH₄OH) release low OH⁻ ions.

pH Scale

• Definition: The pH scale measures the acidity or basicity of a solution.
• pH Values:
  • 0 to 7: Acidic (lower values are more acidic)
  • 7: Neutral
  • 7 to 14: Basic or alkaline (higher values are more basic)

Importance of pH in Everyday Life

The pH scale measures the concentration of hydrogen ions (H⁺) in a solution and ranges from 0 to 14. It is an important parameter in biological, environmental, and industrial processes. Maintaining the proper pH is crucial for human health, the environment, and daily activities.

1. Human Body

• The normal pH range of human blood is 7.0 to 7.8, which is slightly basic.

• Proper pH is essential for enzyme activity and overall metabolism.

• Digestive acids: The stomach produces hydrochloric acid (HCl) to help digest food.

• Excess stomach acid can cause indigestion, irritation, and pain.

• To neutralize excess acid, antacids like milk of magnesia (Mg(OH)₂) or baking soda are used.

2. Acid Rain and Environment

• Rainwater normally has a pH of about 5.6.

• If the pH drops below 5.6 due to pollutants like SO₂ and NO₂, it becomes acid rain.

• Acid rain affects rivers and lakes, making it difficult for aquatic life to survive.

• It can also damage crops, soil quality, and buildings.

3. Dental Health

• When the pH in the mouth falls below 5.5, it can lead to tooth decay.

• Toothpaste, which is slightly basic, helps neutralize acids and protect teeth.

4 Honey Bee Sting:

• The sting contains acidic compounds like formic acid or methanoic acid.

• Treatment: Apply a mild base, such as baking soda (NaHCO₃), to neutralize the acid and relieve pain.

5. Nettle Stings:

• The stinging hairs of nettle release methanoic acid, causing pain on contact.

• Natural Remedy: Rub the affected area with dock plant leaves, which naturally neutralize the acid and reduce irritation

Indicators: 

• Definition: Indicators are substances that change color in the presence of acids or bases.
• Examples of Indicators:
  • Litmus paper (blue turns red in acid, red turns blue in base)
  • Phenolphthalein (colorless in acid, pink in base)
  • Methyl orange (red in acid, yellow in base)

Neutralization:

• Definition: Neutralization is the reaction between an acid and a base, resulting in the formation of salt and water.
• General Equation: Acid + Base → Salt + Water

Applications:

• Acids:
  • Used in industries, laboratories, and daily life (e.g., citric acid in fruits).
• Bases:
  • Used in the manufacture of soaps and detergents.
• Salts:
  • Have various applications, including in food preservation and water treatment.

Key Industrial Compounds and Processes

Chlor-Alkali Process

The Chlor-Alkali Process is an important industrial method for producing sodium hydroxide (NaOH), chlorine gas (Cl₂), and hydrogen gas (H₂).

• Process: Electrolysis of brine (concentrated NaCl solution) decomposes sodium chloride into NaOH, Cl₂, and H₂.

• Importance: NaOH is widely used in soap, paper, and chemical industries; Cl₂ is used in disinfectants and bleaching; H₂ is used as a fuel and in ammonia production.

Bleaching Powder (CaOCl₂)

Preparation: Produced by reacting calcium hydroxide [Ca(OH)₂] with chlorine gas (Cl₂):
Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O

Uses:

• Disinfecting drinking water and swimming pools

• Bleaching cotton, linen, and paper

• Acting as a strong oxidising agent in chemical industries

Baking Soda (NaHCO₃)

Preparation: Baking soda is prepared using sodium chloride (NaCl), ammonia (NH₃), carbon dioxide (CO₂), and water (H₂O) in the Solvay process.

Uses:

• As an antacid to neutralize excess stomach acid

• In baking, it helps dough rise

• Used in fire extinguishers as it releases CO₂ gas when heated

Baking Powder

Composition: A mixture of baking soda (NaHCO₃) and a mild edible acid such as tartaric acid.

Action:

• On mixing with water, it releases carbon dioxide (CO₂) gas, which makes cakes and bread soft and fluffy.

Washing Soda (Na₂CO₃·10H₂O)

Preparation: Obtained by heating sodium carbonate (from soda ash) and then recrystallizing to obtain the decahydrate form.

Uses:

• Cleaning agent for removing grease and stains

• Softens hard water, making it suitable for domestic and industrial purposes

Water of Crystallization

• Some salts contain a fixed number of water molecules in their crystal structure.

• Example: Gypsum (CaSO₄·2H₂O) contains 2 water molecules per formula unit.

• This water is essential for maintaining the crystal structure of the salt.

 Plaster of Paris (POP)

Preparation: Heating gypsum (CaSO₄·2H₂O) at 373 K partially removes water, producing CaSO₄·½H₂O.

Uses:

• Making toys, decorative items, and sculptures

• Smoothing surfaces in interior decoration

• Medical use: casts for fractures

Acid Base and Salt Notes PDF

Acid Base and Salt Class 10 Notes PDF

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