Chapter 5: Acids, Bases and Salts
अम्ल, क्षारक और लवण (लिटमस, हल्दी, फिनोल्फ्थलीन सूचक एवं उदासीनीकरण)
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- Natural Indicators: 1. Litmus (extracted from Lichens): Blue litmus turns RED in acid; Red litmus turns BLUE in base. 2. Turmeric (हल्दी): Yellow in neutral/acid; turns REDDISH-BROWN in base (soap solution). 3. China Rose (गुड़हल): Turns dark pink/magenta in acid; turns GREEN in base.
- Synthetic Indicator Phenolphthalein: Remains COLORLESS in acid; turns deep PINK in base.
- Neutralization Reaction: Acid + Base -> Salt + Water + Heat (Exothermic reaction).
- Real-Life Neutralization: 1. Indigestion (अम्लता): Milk of Magnesia (Magnesium hydroxide) neutralizes excess hydrochloric acid in stomach. 2. Ant Sting: Contains Formic Acid; neutralized by moist baking soda (Sodium hydrogen carbonate) or Calamine solution (Zinc carbonate). 3. Soil Treatment: Acidic soil treated with quicklime (Calcium oxide) or slaked lime; basic soil treated with organic manure.
- Trap: What color does turmeric turn in base (soap)? Correct: **Reddish-brown (लाल-भूरा)**, NOT green or blue.
- Trap: What does ant sting inject? Correct: **Formic acid**; neutralized using **Calamine (zinc carbonate) or baking soda**.
- Trap: What color does China rose indicator turn in basic solution? Correct: **Green (हरा)**.
NCERT Core Facts: Chemical Indicators & Everyday Neutralization
In CTET Paper 2 Science, acid-base indicators and neutralization reactions appear in every single question paper:
1. Master Indicator Color Matrix
| Indicator | Source | Color in Neutral Solution | Color in Acid (अम्ल) | Color in Base (क्षारक) |
|---|---|---|---|---|
| Litmus (लिटमस) | Lichens (लाइकेन) | Purple (Mauve) | Turns RED (लाल) | Turns BLUE (नीला) |
| Turmeric (हल्दी) | Plant rhizome | Yellow | Remains YELLOW | Turns REDDISH-BROWN (लाल-भूरा) |
| China Rose (गुड़हल) | Petal extract | Light pink | Dark Pink / Magenta | Turns GREEN (हरा) |
| Phenolphthalein | Synthetic indicator | Colorless | COLORLESS (रंगहीन) | Deep PINK (गुलाबी) |
2. Real-World Applications of Neutralization (उदासीनीकरण)
- Ant Sting Treatment:
- When an ant bites, it injects acidic Formic Acid into the skin.
- Neutralized by rubbing mild bases: Baking Soda (NaHCO_3) or Calamine lotion (containing Zinc Carbonate).
- Stomach Indigestion:
- Excessive gastric HCl causes acidity.
- Neutralized using Antacids such as Milk of Magnesia (Mg(OH)_2).
Test Your Mastery: Acids, Bases and Salts
Authentic CBSE exam questions tested directly from this NCERT chapter.
A student drops a few drops of phenolphthalein indicator into test tube A containing dilute hydrochloric acid, and test tube B containing sodium hydroxide solution. What colors will be observed in A and B respectively?
एक विद्यार्थी परखनली A (तनु हाइड्रोक्लोरिक अम्ल) और परखनली B (सोडियम हाइड्रोक्साइड) में फिनोल्फ्थलीन सूचक की कुछ बूँदें डालता है। A और B में क्रमशः कौन-से रंग दिखाई देंगे?
Turmeric indicator turns reddish-brown when brought in contact with solution X. Solution X could be:
हल्दी का सूचक विलयन X के संपर्क में आने पर लाल-भूरा हो जाता है। विलयन X क्या हो सकता है?
What acid is present in an ant's sting, and how is it neutralized?
Formic acid; it is neutralized by applying moist baking soda or calamine solution.
What color change occurs when soap solution is added to turmeric paper?
The yellow turmeric turns reddish-brown because soap is basic.