Acidity and Basicity

Acidity and basicity are key concepts in chemistry, determining the behavior of substances in digestion, cleaning, agriculture, and industries. Their properties depend on hydrogen ions (H⁺) and hydroxide ions (OH⁻).

1. Definition

• Acid (अम्ल): Produces H⁺ ions in water. Sour taste, corrosive.
• Base (क्षार): Produces OH⁻ ions or accepts H⁺. Bitter, slippery.

2. Acid-Base Theories

• Arrhenius: Acids ↑ H⁺, Bases ↑ OH⁻ (limited to aqueous solutions).
• Brønsted–Lowry: Acids donate H⁺, Bases accept H⁺.
• Lewis: Acids = electron pair acceptors, Bases = donors.

3. pH Scale

pH = -log[H⁺]

• pH 0–6.9 = Acidic
• pH 7 = Neutral
• pH 7.1–14 = Basic

4. Indicators

Indicator	In Acid	In Base
Litmus	Red	Blue
Phenolphthalein	Colorless	Pink
Methyl Orange	Red	Yellow

5. Applications

• Digestive System: HCl aids digestion.
• Antacids: Mg(OH)₂ neutralizes excess acid.
• Soil: Lime corrects acidic soil.
• Cleaning: Soaps are basic.
• Acid Rain: SO₂ + NO₂ in rainwater ↓ pH.

6. Neutralization

HCl + NaOH → NaCl + H₂O

Interactive Quiz

Q1: What is the pH of a neutral solution?

• 5
• 7 ✅
• 9
• 14

Explanation: Pure water has pH 7, which is neutral.

Q2: Which indicator turns pink in base?

• Methyl Orange
• Phenolphthalein ✅
• Litmus
• Turmeric

Explanation: Phenolphthalein is colorless in acids but turns pink in bases.

True / False

• Acids taste bitter. ❌ (They are sour.)
• Bases feel slippery. ✅

Fill in the Blanks

• pH of neutral water is __7__.
• Lewis acid is an electron pair __acceptor__.

FAQs

Q1: Why is pH important?

Ans: It helps monitor health, soil, water, and industry quality control.

Q2: What is acid rain?

Ans: Rainwater with dissolved SO₂/NO₂, lowering its pH, harmful to plants and buildings.

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Learn more about pH on Wikipedia