Quick Revision Notes & Formula Sheet

Class: 7th Science
Chapter: Acids, Bases and Salts (अम्ल, क्षारक और लवण)

### 1. Introduction to Acids and Bases (अम्ल और क्षारक का परिचय)

• Acids (अम्ल):
  • Substances that taste sour (खट्टे).
  • Turn blue litmus to red.
  • They are corrosive in nature.
  • Examples: Lemon juice, vinegar, tamarind, hydrochloric acid.
• Bases (क्षारक):
  • Substances that taste bitter (कड़we) and feel soapy to touch.
  • Turn red litmus to blue.
  • Examples: Baking soda, soap, lime water, caustic soda.

### 2. Indicators (सूचक)

Indicators are special substances used to test whether a substance is acidic or basic. They change their color in the presence of an acid or a base.

• Natural Indicators (प्राकृतिक सूचक):

  • Litmus (लिटमस): Extracted from lichens (लाइकेन).
    • In Acid: Blue turns to Red.
    • In Base: Red turns to Blue.
  • Turmeric (हल्दी):
    • In Acid: No change (remains yellow).
    • In Base: Turns bright red/brownish-red.
  • China Rose / Gudhal Petals (गुड़हल के फूल):
    • In Acid: Turns dark pink (magenta).
    • In Base: Turns green.

• Synthetic Indicators (कृत्रिम सूचक):

  • Phenolphthalein (फिनॉल्फ्थलीन):
    • In Acid: Colorless.
    • In Base: Pink.

### 3. Neutralisation (उदासीनीकरण)

• Definition: The reaction between an acid and a base is known as neutralisation. Salt and water are produced in this process with the evolution of heat.
• Word Equation: $$\text{Acid (अम्ल)} + \text{Base (क्षारक)} \rightarrow \text{Salt (लवण)} + \text{Water (जल)} + \text{Heat (ऊष्मा)}$$
• Example: $$\text{Hydrochloric acid (HCl)} + \text{Sodium hydroxide (NaOH)} \rightarrow \text{Sodium chloride (NaCl)} + \text{Water (H}_2\text{O)}$$

### 4. Neutralisation in Everyday Life (दैनिक जीवन में उदासीनीकरण)

1. Indigestion (अपरचन / एसिडिटी):
   • Our stomach contains hydrochloric acid which helps in digestion. Too much acid causes indigestion.
   • Remedy: Taken an antacid like milk of magnesia (magnesium hydroxide) which neutralises the excess acid.
2. Ant Bite (चींटी का डंक):
   • When an ant bites, it injects formic acid into the skin.
   • Remedy: Rubbing moist baking soda (sodium hydrogen carbonate) or calamine solution (zinc carbonate) neutralises the acid.
3. Soil Treatment (मृदा उपचार):
   • Too acidic soil: Treated with bases like quicklime (calcium oxide) or slaked lime (calcium hydroxide).
   • Too basic soil: Treated by adding organic matter (compost) which releases acids to neutralise the base.
4. Factory Wastes (कारखानों का कचरा):
   • Factory wastes contain acids. If allowed to flow into water bodies, they kill fish. Hence, wastes are neutralised by adding basic substances before discharging them.

### 5. Common Acids and their Sources (प्रमुख अम्ल और उनके स्रोत)

### 6. Common Bases and their Sources (प्रमुख क्षारक और उनके स्रोत)