ACIDS, BASES AND SALTS
Class 10 Science | Chapter 2
Complete Chapter Notes & Important Chemical Reactions
Reading progress
📚 Chapter Contents
1. Chemical Properties of Acids and Bases 2. Common Properties of Acids and Bases 3. Strength of Acid and Base Solutions – pH Scale 4. More About Salts 5. Important Chemical Equations 6. Quick Revision 7. Interactive MCQ Practice1. Chemical Properties of Acids and Bases
What is an Acid?
An acid is a chemical compound that has a distinct sour flavour and possesses acidic properties. Chemically, it is characterized by a pH value less than 7.
Types of Acids
| Type | Definition | Examples |
|---|---|---|
| Strong Acids | Dissociate completely or almost completely in water. | HCl, H₂SO₄, HNO₃ |
| Weak Acids | Dissociate partially in water. | CH₃COOH, Oxalic acid, Lactic acid |
| Concentrated Acids | Contain a high amount of acid and less water. | Concentrated H₂SO₄ |
| Dilute Acids | Contain a lower amount of acid and more water. | 5% H₂SO₄ solution |
What is a Base?
A base is a chemical compound that has a distinct bitter taste and basic properties. It is characterized by a pH value greater than 7.
Types of Bases
| Type | Definition | Examples |
|---|---|---|
| Strong Bases | Ionize completely in water. | NaOH, KOH, Ca(OH)₂ |
| Weak Bases | Partially ionize in water. | NH₄OH |
| Alkalis | Bases that are soluble in water. | NaOH, KOH, Ca(OH)₂ |
Indicators and Laboratory Activities
An indicator is a chemical compound that changes its colour in the presence of an acid or a base. Indicators are generally derived from plant pigments and are mildly acidic or basic in nature.
| Indicator | In Acid | In Base |
|---|---|---|
| Blue Litmus | Turns red | Remains blue |
| Red Litmus | Remains red | Turns blue |
| Universal Indicator | Red / Orange / Yellow | Blue / Violet |
Activity 2: Testing olfactory indicators.
Reaction of Acids and Bases with Metals
Acids react with metals to displace hydrogen, forming a salt and releasing hydrogen gas.
Bases generally do not react with all metals. However, amphoteric metals like zinc react with bases to form salts and hydrogen gas.
Reaction of Metal Carbonates and Hydrogencarbonates with Acids
Reaction 1:
Reaction 2:
Testing Carbon Dioxide Gas
Passing carbon dioxide through lime water turns it milky due to the formation of calcium carbonate.
When excess CO₂ is passed, the milkiness disappears.
Neutralization Reaction
The reaction between an acid and a base is known as a neutralization reaction. They react to form salt and water.
Types of Neutralization Reactions
| Reactants | Salt Type | Example | pH |
|---|---|---|---|
| Strong acid + Weak base | Acidic salt | HCl + NH₄OH → NH₄Cl + H₂O | Below 7 |
| Weak acid + Strong base | Basic salt | CH₃COOH + NaOH → CH₃COONa + H₂O | Above 7 |
| Strong acid + Strong base | Neutral salt | H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O | 7 |
| Weak acid + Weak base | Depends on solution | CH₃COOH + NH₃ → CH₃COONH₄ + H₂O | Determine experimentally |
Reaction of Metallic Oxides with Acids
Metallic oxides react with acids to produce salt and water. They are classified as basic oxides, although some are amphoteric.
Reaction of Non-metallic Oxides with Bases
Non-metallic oxides are acidic in nature and react with bases to form salt and water.
2. What Do All Acids and Bases Have in Common?
Common Characteristics
- Electrolytes: Both acids and bases conduct electricity when dissolved in water due to free-moving ions.
- Neutralization: Both react with each other to form salt and water.
- Indicator Colour Change: Acids turn blue litmus red, while bases turn red litmus blue.
- Ion Production: Their strength depends on the degree of dissociation into ions in water.
What Happens to Acids in Water?
Acids produce H⁺ ions in the presence of water. Since H⁺ ions cannot exist independently, they combine with water molecules to form hydronium ions (H₃O⁺).
What Happens to Bases in Water?
Bases dissolve in water to yield hydroxide ions (OH⁻). Water-soluble bases are known as alkalis.
Overall Neutralization in Ionic Form
3. How Strong Are Acid or Base Solutions? – pH Scale
The strength of an acid or base solution is measured using the pH scale or estimated using a Universal Indicator.
pH Scale
Acidic ←──────── Neutral ────────→ Basic
Importance of pH in Everyday Life
1. Biological Sensitivity
2. Soil pH for Crop Growth
3. Human Digestive System
4. Tooth Decay Prevention
5. Self-Defence in Animals and Plants
4. More About Salts
What is a Salt?
A salt is an ionic compound formed when an acid reacts with a base.
Examples:
- Sodium Chloride – NaCl
- Epsom Salt – MgSO₄
Family of Salts and pH
Salts sharing the same cation or anion belong to the same family. For example, NaCl, KCl and LiCl belong to the chloride family.
| Combination | Nature of Salt | pH |
|---|---|---|
| Strong acid + Strong base | Neutral | ≈ 7 |
| Weak acid + Strong base | Basic | > 7 |
| Strong acid + Weak base | Acidic | < 7 |
| Weak acid + Weak base | Experimental determination | Depends |
Chemicals Derived from Common Salt (NaCl)
Common salt is a raw material for producing several important industrial chemicals.
1. Sodium Hydroxide – NaOH
Common name: Caustic Soda
Process: Chlor-alkali process.
Uses: Soaps, detergents, paper manufacturing and bleach.
2. Bleaching Powder – CaOCl₂
Common name: Calcium Oxychloride
Uses: Textile bleaching, disinfecting drinking water and as an oxidizer.
3. Baking Soda – NaHCO₃
Common name: Sodium Hydrogencarbonate
Uses: Baking powder ingredient, antacid and soda-acid fire extinguishers.
4. Washing Soda – Na₂CO₃·10H₂O
Common name: Sodium Carbonate Decahydrate
Uses: Glass, soap, paper, household cleaning and removing water hardness.
Are Crystals Really Dry? – Water of Crystallization
Many salt crystals contain a fixed number of water molecules bound within their crystalline structure. This water is termed the water of crystallization.
1. Copper Sulfate Crystals
Blue copper sulfate crystals contain five molecules of water. Heating drives off water, turning the salt white. Adding water restores the blue colour.
2. Gypsum and Plaster of Paris
Gypsum contains two water molecules per formula unit. When heated to 100°C (373 K), it loses 1.5 water molecules to form Plaster of Paris.
5. Important Chemical Equations
| No. | Reaction |
|---|---|
| 1 | 2HCl + Zn → ZnCl₂ + H₂ |
| 2 | 2NaOH + Zn → Na₂ZnO₂ + H₂ |
| 3 | 2HCl + Na₂CO₃ → 2NaCl + CO₂ + H₂O |
| 4 | HCl + NaHCO₃ → NaCl + CO₂ + H₂O |
| 5 | Ca(OH)₂ + CO₂ → CaCO₃ + H₂O |
| 6 | H⁺ + OH⁻ → H₂O |
| 7 | CaO + 2HCl → CaCl₂ + H₂O |
| 8 | SO₂ + 2NaOH → Na₂SO₃ + H₂O |
| 9 | 2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂ |
| 10 | Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O |
| 11 | NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃ |
| 12 | 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂ |
6. Quick Revision
- Acids have pH less than 7.
- Bases have pH greater than 7.
- Neutral solutions have pH equal to 7.
- Acids produce hydrogen ions in water.
- Bases produce hydroxide ions in water.
- Acid + Base produces salt and water.
- Acid + Metal produces salt and hydrogen gas.
- Metal carbonate + Acid produces salt, carbon dioxide and water.
- Common salt is sodium chloride (NaCl).
- Water of crystallization is water present in the crystal structure of salts.
7. Interactive MCQ Practice
Test your understanding of Acids, Bases and Salts.
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