Notes on Acids, Bases, and Salts

Acids

Definition:

Substances that produce hydrogen ions (H⁺) when dissolved in water.

Examples:

- Hydrochloric acid (HCl)

- Sulphuric acid (H₂SO₄)

- Nitric acid (HNO₃)

- Acetic acid (CH₃COOH)

Types of Acids:

1. Inorganic Acids: Acids without carbon atoms (except H₂CO₃). Strong acids.

   Examples: HCl, H₂SO₄, HNO₃.

2. Organic Acids: Acids containing carbon, derived from plants or animals. Weak acids.

   Examples:

   - Acetic acid (CH₃COOH) - Vinegar

   - Citric acid (C₆H₈O₇) - Lemon, Tomato

   - Ascorbic acid (Vitamin C, C₆H₈O₆) - Fruits and vegetables

Properties:

1. Sour taste (except some like boric acid).

2. Turns blue litmus red.

3. Corrosive and can damage skin.

4. React with metals to produce hydrogen gas.

Uses:

- Sulphuric acid: Fertilizers, detergents.

- Hydrochloric acid: PVC manufacturing.

- Nitric acid: Plastics, explosives.

- Acetic acid: Flavoring, pickling.

- Ascorbic acid: Vitamin C source.

Bases

Definition:

Substances that produce hydroxide ions (OH⁻) when dissolved in water.

(A base is a metallic oxide, hydroxide, or a compound that produces hydroxide ions (OH⁻) when dissolved in water.) 

Examples:

1. Calcium Oxide (CaO): CaO + H₂O → Ca²⁺ + 2OH⁻

2. Calcium Hydroxide [Ca(OH)₂]: Ca(OH)₂ → Ca²⁺ + 2OH⁻

3. Sodium Hydroxide (NaOH): NaOH → Na⁺ + OH⁻

4. Magnesium Hydroxide [Mg(OH)₂]: Mg(OH)₂ → Mg²⁺ + 2OH⁻

5. Ammonia (NH₃): NH₃ + H₂O → NH₄⁺ + OH⁻

Types of Bases

1. Oxides: Metallic oxides that react with water to form hydroxides.

Examples: Na₂O, MgO, CaO.

2. Hydroxides: Compounds derived from water where hydrogen is replaced by metals.

Examples: NaOH, KOH, Ca(OH)₂.

Properties of Bases

1. Physical Properties:

- Bitter taste (except Mg(OH)₂ and Al(OH)₃ which are safe in small amounts).

- Slippery to touch.

- Changes indicators:

  - Red litmus → Blue.

  - Methyl orange → Yellow.

  - Phenolphthalein → Pink.

- Strong bases have corrosive effects.

2. Chemical Properties:

- Produce hydroxide ions (OH⁻) in water.

- React with acids to form salt and water (Neutralization).

- React with carbon dioxide to form carbonates.

Uses of Bases in Daily Life

1. Firewood Ash (Na₂O, K₂O): Used in washing clothes and utensils.

2. Sodium Hydroxide (NaOH): Used in making soap and paper.

3. Magnesium Hydroxide (Mg(OH)₂): Used as an antacid for gastric disorders.

4. Calcium Hydroxide [Ca(OH)₂]: Removes water hardness.

5. Ammonium Hydroxide (NH₄OH): Used in fertilizers and plastics.

Reactions Involving Bases

1. Reaction with Water: Bases dissolve in water to release hydroxide ions (OH⁻).

Example: NaOH → Na⁺ + OH⁻

2. Reaction with Acids (Neutralization): Bases react with acids to form salt and water.

Example: NaOH + HCl → NaCl + H₂O

3. Reaction with Carbon Dioxide: Bases react with CO₂ to form carbonates.

Example: Ca(OH)₂ + CO₂ → CaCO₃ + H₂O

4. Reaction with Salts: Bases react with certain salts to form insoluble hydroxides.

Example: AlCl₃ + 3NaOH → Al(OH)₃ + 3NaCl

Salt

- Definition: A compound formed when the hydrogen of an acid is replaced by a metal.

Formation:

  - Acid + Base → Salt + Water (Neutralization reaction)

  - Examples:

    - Hydrochloric acid (HCl) + Sodium hydroxide (NaOH) → Sodium chloride (NaCl) + H₂O.

Examples of Salts:

1. Sodium chloride (NaCl)

2. Zinc sulphate (ZnSO₄)

3. Calcium carbonate (CaCO₃)

4. Magnesium nitrate (Mg(NO₃)₂)

Types of Salts

1. Neutral Salts: Formed when strong acids react with strong bases.

   - Examples: NaCl, KNO₃, K₂SO₄

2. Acidic Salts: Formed when strong acids react with weak bases.

   - Examples: CuSO₄, NH₄Cl

3. Basic Salts: Formed when strong bases react with weak acids.

   - Examples: Na₂CO₃, NaHCO₃

Properties of Salts

1. Some salts are soluble in water (e.g., NaCl), while others are insoluble (e.g., AgCl).

2. Salts may be colorless or colored (e.g., CuSO₄ is blue).

3. Salts conduct electricity in aqueous solutions.

4. They may exist as crystalline or amorphous solids.

Indicators for Testing Acidity/Basicity

1. Red litmus: Turns blue in basic solutions.

2. Methyl orange: Turns yellow in bases.

3. Phenolphthalein: Turns pink in basic solutions.

4. Universal Indicator: Shows different colors for different pH levels.

Chemical Properties of Salts

1. Dissociation in Water

Salts dissociate into positive and negative ions in water.

Example: NaCl → Na⁺ + Cl⁻

2. Reaction with Bases

Salts react with bases to produce another salt and base.

Example: 2NH₄Cl + Ca(OH)₂ → CaCl₂ + 2NH₃ + 2H₂O

3. Reaction with Acids

Salts react with acids to form another salt and acid.

Example: 2NaCl + H₂SO₄ → Na₂SO₄ + 2HCl

4. Metal Replacement

A less reactive metal in a salt is replaced by a more reactive metal.

Example: CuSO₄ + Fe → FeSO₄ + Cu

Salts Used in Daily Life

Sodium Chloride (NaCl): Used in food preparation.

Copper Sulphate (CuSO₄): Used as a fungicide.

Calcium Sulphate (CaSO₄): Used in plaster for fractures.

Magnesium Sulphate (MgSO₄): Used as medicine for constipation.

Sodium Bicarbonate (NaHCO₃): Used in baking powder and medicine.

Sodium Carbonate (Na₂CO₃): Used in making soap and detergent.

Ammonium Sulphate ((NH₄)₂SO₄): Used as a chemical fertilizer.

Indicators

1. Definition

Substances that show whether a chemical is acidic, basic, or neutral by changing color.

Examples:

- Litmus: Red in acids, blue in bases.

- Universal Indicator: Shows pH range (red-yellow-green-blue).

2. Natural Indicator Preparation

- Grind flower petals into a paste.

- Add water and alcohol to extract pigments.

- Use as litmus paper to test acids and bases.

pH Scale

1. Definition

A scale from 1 to 14 indicating acidity or alkalinity.

- pH < 7: Acidic.

- pH = 7: Neutral.

- pH > 7: Alkaline.

2. pH Meter

Device to measure the concentration of hydrogen ions (H⁺) in a solution.