🧪 Acids, Bases and Salts

Class X Chemistry • Chapter 1 • Enhanced Interactive Study Guide

By S.K.Sinha • Free Test Maker.com

🌟 Introduction

Welcome to the fascinating world of acids, bases, and salts! These substances are all around us - from the citric acid in lemons to the sodium hydroxide in soap. Understanding their properties and behavior is crucial for chemistry success.

Common Examples Around Us

🍋
Acid
🧼
Base
🧂
Salt

🔬 Understanding Acids

Definition: Acids are substances that release hydrogen ions (H⁺) when dissolved in water.

🧪 Properties of Acids

  • Taste: Sour taste (⚠️ Never taste unknown chemicals!)
  • Touch: Corrosive to skin and metals
  • Indicators: Turn blue litmus paper red
  • Conductivity: Conduct electricity in aqueous solution
  • pH: Less than 7

Common Acids & Their Uses

Acid Chemical Formula Common Source Uses
Hydrochloric Acid HCl Stomach acid Digestion, cleaning
Sulfuric Acid H₂SO₄ Car batteries Industrial processes
Citric Acid C₆H₈O₇ Citrus fruits Food preservation
Acetic Acid CH₃COOH Vinegar Cooking, cleaning
General Reaction:
Acid + Water → H⁺ + Anion⁻
Example: HCl + H₂O → H⁺ + Cl⁻

🧪 Understanding Bases

Definition: Bases are substances that release hydroxide ions (OH⁻) when dissolved in water.

🔬 Properties of Bases

  • Taste: Bitter taste (⚠️ Never taste unknown chemicals!)
  • Touch: Slippery/soapy feel
  • Indicators: Turn red litmus paper blue
  • Conductivity: Conduct electricity in aqueous solution
  • pH: Greater than 7

Common Bases & Their Uses

Base Chemical Formula Common Source Uses
Sodium Hydroxide NaOH Soap making Cleaning, paper industry
Calcium Hydroxide Ca(OH)₂ Lime water Whitewashing, neutralizing
Magnesium Hydroxide Mg(OH)₂ Milk of magnesia Antacid, laxative
Ammonia NH₃ Cleaning products Fertilizers, cleaning
General Reaction:
Base + Water → OH⁻ + Cation⁺
Example: NaOH + H₂O → Na⁺ + OH⁻

🎨 Acid-Base Indicators

Indicators: Substances that change color in acidic and basic solutions, helping us identify the nature of unknown solutions.

🔴 Litmus Paper

Natural Source: Lichens

In Acid: Blue → Red

In Base: Red → Blue

Neutral: No change

🟡 Turmeric

Natural Source: Turmeric powder

In Acid: Yellow (no change)

In Base: Yellow → Red

Uses: Kitchen indicator

🟣 Red Cabbage

Natural Source: Red cabbage extract

In Acid: Red/Pink

In Base: Green/Blue

Special: Multiple color changes

🌺 Phenolphthalein

Type: Synthetic indicator

In Acid: Colorless

In Base: Pink/Magenta

Uses: Laboratory titrations

🧪 Universal Indicator

Shows different colors for different pH values:

0-1
Strong Acid
2-3
Weak Acid
4-5
Weak Acid
6
Weak Acid
7
Neutral
8
Weak Base
9-10
Weak Base
11-12
Strong Base
13-14
Strong Base

⚡ Acids and Bases in Water

H⁺
OH⁻
H₂O

💧 What happens when acids and bases dissolve in water?

When acids dissolve in water, they release H⁺ ions. When bases dissolve in water, they release OH⁻ ions. These ions are responsible for the properties of acidic and basic solutions.

Key Points:

  • Acids increase H⁺ concentration in water
  • Bases increase OH⁻ concentration in water
  • Pure water has equal H⁺ and OH⁻ concentrations
  • pH scale measures H⁺ concentration
  • Lower pH = more acidic, Higher pH = more basic
Water Ionization:
H₂O ⇌ H⁺ + OH⁻
At 25°C: [H⁺] × [OH⁻] = 10⁻¹⁴

🔥 Strong vs Weak Acids and Bases

Property Strong Acids/Bases Weak Acids/Bases
Ionization Complete ionization Partial ionization
pH (Acids) Very low (0-2) Moderate (3-6)
pH (Bases) Very high (12-14) Moderate (8-11)
Conductivity High Low
Examples (Acids) HCl, HNO₃, H₂SO₄ CH₃COOH, H₂CO₃
Examples (Bases) NaOH, KOH, Ca(OH)₂ NH₃, Mg(OH)₂
Degree of Ionization (α) =
Number of molecules ionized / Total number of molecules
Strong: α ≈ 1 (100%), Weak: α < 1 (< 100%)

🧂 How Important is pH in Everyday Life?

🏥 pH in Human Body

  • Blood pH: 7.35-7.45 (slightly basic)
  • Stomach pH: 1.5-3.5 (highly acidic)
  • Saliva pH: 6.5-7.5 (nearly neutral)
  • Urine pH: 4.5-8.0 (varies with diet)

🌱 pH in Agriculture

  • Optimal soil pH: 6.0-7.0 for most crops
  • Acidic soil: Add lime (Ca(OH)₂) to neutralize
  • Basic soil: Add organic matter or sulfur
  • pH testing: Essential for crop productivity

Why pH Matters:

  • Enzyme activity depends on pH
  • Nutrient availability in soil
  • Water quality for drinking
  • Food preservation and taste
  • Industrial processes

⚗️ Neutralization Reactions

Neutralization: The reaction between an acid and a base to form salt and water.
General Neutralization Reaction:
Acid + Base → Salt + Water
Example: HCl + NaOH → NaCl + H₂O

🔬 Types of Neutralization

Acid Base Salt Formed pH of Salt
Strong Acid Strong Base Neutral Salt pH = 7
Strong Acid Weak Base Acidic Salt pH < 7
Weak Acid Strong Base Basic Salt pH > 7
Weak Acid Weak Base Depends on strength pH ≈ 7

🧪 Common Neutralization Examples

1. HCl + NaOH → NaCl + H₂O
(Hydrochloric acid + Sodium hydroxide → Sodium chloride + Water)
2. H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O
(Sulfuric acid + Sodium hydroxide → Sodium sulfate + Water)
3. HNO₃ + KOH → KNO₃ + H₂O
(Nitric acid + Potassium hydroxide → Potassium nitrate + Water)

🧂 Salts and Their Properties

Salt: An ionic compound formed by the neutralization of an acid with a base.

🔬 Properties of Salts

  • Ionic Nature: Made of positive and negative ions
  • Crystalline Structure: Form regular crystal patterns
  • Solubility: Most salts are soluble in water
  • Conductivity: Conduct electricity when dissolved
  • Taste: Can be salty, bitter, or neutral

🧂 Common Salts and Their Uses

Salt Chemical Formula Common Name Uses
Sodium Chloride NaCl Table Salt Cooking, food preservation
Calcium Carbonate CaCO₃ Limestone, Marble Construction, antacids
Sodium Bicarbonate NaHCO₃ Baking Soda Baking, cleaning, antacid
Potassium Nitrate KNO₃ Saltpeter Fertilizers, fireworks
Copper Sulfate CuSO₄ Blue Vitriol Fungicides, electroplating

🔬 Salt Formation Process

Step 1: Acid releases H⁺ ions
Step 2: Base releases OH⁻ ions
Step 3: H⁺ + OH⁻ → H₂O (water)
Step 4: Remaining ions form salt

💧 Water of Crystallization

Water of Crystallization: The fixed number of water molecules present in one formula unit of a salt.

🧪 Examples of Hydrated Salts

Hydrated Salt Formula Common Name Water Molecules
Copper Sulfate CuSO₄·5H₂O Blue Vitriol 5
Sodium Carbonate Na₂CO₃·10H₂O Washing Soda 10
Magnesium Sulfate MgSO₄·7H₂O Epsom Salt 7
Calcium Sulfate CaSO₄·2H₂O Gypsum 2
Heating Effect:
CuSO₄·5H₂O → CuSO₄ + 5H₂O
(Blue crystals → White powder + Water vapor)

Important Points:

  • Water molecules are part of the crystal structure
  • Removal of water changes color and properties
  • Process is usually reversible
  • Essential for maintaining crystal structure

🏭 Preparation of Salts

🔬 Methods of Salt Preparation

Method 1: Acid + Base

HCl + NaOH → NaCl + H₂O
Direct neutralization method

Method 2: Acid + Metal

Zn + 2HCl → ZnCl₂ + H₂↑
Metal displacement method

Method 3: Acid + Metal Oxide

CuO + H₂SO₄ → CuSO₄ + H₂O
Oxide neutralization method

Method 4: Acid + Metal Carbonate

CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑
Carbonate displacement method

⚗️ Chemicals from Common Salt

Common Salt (NaCl): The most important raw material for producing various chemicals.

🧂 Common Salt Family Tree

NaCl

Common Salt

Source of all sodium compounds

NaOH

Sodium Hydroxide

Caustic soda, soap making

Na₂CO₃

Sodium Carbonate

Washing soda, glass making

NaHCO₃

Sodium Bicarbonate

Baking soda, fire extinguisher

🏭 Industrial Production

1. Sodium Hydroxide (Chlor-alkali Process)

2NaCl + 2H₂O → 2NaOH + Cl₂↑ + H₂↑
Electrolysis of brine solution
  • Uses: Soap, paper, textiles
  • By-products: Chlorine gas, Hydrogen gas
  • Process: Electrolysis

2. Sodium Carbonate (Solvay Process)

NaCl + NH₃ + CO₂ + H₂O → NaHCO₃ + NH₄Cl
2NaHCO₃ → Na₂CO₃ + H₂O + CO₂↑
Multi-step chemical process
  • Uses: Glass making, paper, detergents
  • Also called: Washing soda
  • Formula: Na₂CO₃·10H₂O

3. Sodium Bicarbonate

Na₂CO₃ + H₂O + CO₂ → 2NaHCO₃
Reaction with carbon dioxide
  • Uses: Baking, antacid, fire extinguisher
  • Also called: Baking soda
  • Mild base, safe for consumption

🧪 Interactive Quiz Section

1. Which indicator turns red in basic solution?
A) Turmeric
B) Litmus
C) Phenolphthalein
D) Methyl orange
2. What is the pH of pure water at 25°C?
A) 0
B) 7
C) 14
D) 1
3. Which salt is known as 'Blue Vitriol'?
A) FeSO₄·7H₂O
B) CuSO₄·5H₂O
C) ZnSO₄·7H₂O
D) MgSO₄·7H₂O

📚 Summary & Key Takeaways

🎯 Chapter Summary:

  • Acids release H⁺ ions, bases release OH⁻ ions in water
  • pH scale ranges from 0-14, with 7 being neutral
  • Indicators help identify acids and bases by color changes
  • Neutralization produces salt and water
  • Salts can be acidic, basic, or neutral depending on parent compounds
  • Common salt (NaCl) is the source of many important chemicals
  • Water of crystallization is essential for crystal structure

🔬 Important Formulas to Remember

pH + pOH = 14
pH = -log[H⁺]
Acid + Base → Salt + Water
[H⁺] × [OH⁻] = 10⁻¹⁴

🎓 Study Tips

🚀 Practice Problems

🧪 Problem Set 1: Identification

  1. A solution has pH = 3. Is it acidic or basic? What color will it show with litmus?
  2. Name the acid present in: (a) Vinegar (b) Lemon (c) Stomach
  3. What happens when blue litmus is dipped in lime water?

⚗️ Problem Set 2: Reactions

  1. Complete: HCl + Ca(OH)₂ → ___ + ___
  2. What gas is evolved when zinc reacts with hydrochloric acid?
  3. Write the formula for: (a) Washing soda (b) Baking soda (c) Gypsum

🔬 Problem Set 3: Applications

  1. Why is sodium hydrogen carbonate used in fire extinguishers?
  2. What is the role of calcium hydroxide in whitewashing?
  3. How is common salt converted to washing soda?

🎉 Congratulations!

You have completed Chapter 1: Acids, Bases and Salts! 🎓

"Chemistry is not just about memorizing formulas, it's about understanding the world around us!" 🌟

freetestmaker.com
📚 freetestmaker.com | Anonymous | 2025-10-31 22:06:18