Quick Revision Notes & Formula Sheet

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

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### 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.

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### 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.

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### 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: $$\text{Hydrochloric acid (HCl)} + \text{Sodium hydroxide (NaOH)} \rightarrow \text{Sodium chloride (NaCl)} + \text{Water (H}_2\text{O)}$$

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### 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.

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

Acid (अम्ल)	Natural Source (प्राकृतिक स्रोत)
Acetic Acid	Vinegar (सिरका)
Formic Acid	Ant sting (चींटी का डंक)
Citric Acid	Citrus fruits like oranges, lemons (खट्टे फल)
Lactic Acid	Curd (दही)
Oxalic Acid	Spinach (पालक)
Ascorbic Acid (Vitamin C)	Amla, citrus fruits (आँवला, नीबू)
Tartaric Acid	Tamarind, grapes, unripe mangoes (इमली, अंगूर)

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

Base (क्षारक)	Found in (किसमें पाया जाता है)
Calcium Hydroxide	Lime water (चूने का पानी)
Ammonium Hydroxide	Window cleaner (खिड़की साफ करने के कांच)
Sodium Hydroxide / Potassium Hydroxide	Soap (साबुन)
Magnesium Hydroxide	Milk of magnesia (मिल्क ऑफ मैग्नीशिया)