Chapter 2: Acids, Bases, and Salts
Comprehensive Study Notes & Concept Guide
Welcome to this detailed guide on Acids, Bases, and Salts. This chapter is essential for understanding the chemical nature of substances we interact with daily—from the food we eat to the medicines we take.
1. Indicators: The Identity Detectors
Indicators are substances that change their properties (like color or smell) when they come in contact with an acid or a base.
- Natural: Litmus (Purple dye from Lichens), Turmeric.
- Synthetic: Methyl Orange, Phenolphthalein.
- Olfactory: Vanilla, Onion, Clove (Smell changes in base).
| Indicator | Acidic Medium | Basic Medium |
|---|---|---|
| Blue Litmus | Red | No Change |
| Red Litmus | No Change | Blue |
| Phenolphthalein | Colorless | Pink |
2. Properties of Acids
Physical: Sour taste, turn blue litmus red, and conduct electricity in aqueous form.
Chemical: Acids release H+ ions in water.
Key Chemical Reactions:
A. Reaction with Metal: Releases Hydrogen gas ($H_2$).
Example: Zn + H2SO4 → ZnSO4 + H2 ↑
B. Reaction with Carbonates: Releases Carbon Dioxide ($CO_2$).
3. Properties of Bases
Bases are bitter in taste and soapy to touch. Water-soluble bases are called Alkalis.
Neutralization Reaction:
When an acid and base react, they form salt and water, neutralizing each other.
4. The pH Scale
The strength of acids and bases is measured on a scale of 0-14 called the pH scale.
- pH < 7: Acidic (0 is very acidic)
- pH = 7: Neutral (Pure Water)
- pH > 7: Basic (14 is very alkaline)
pH in Everyday Life:
- Stomach: Produces HCl (pH ~1.2) for digestion.
- Tooth Decay: Starts if mouth pH is below 5.5.
- Plants: Require specific soil pH for growth.
5. Important Chemical Compounds
A. Sodium Hydroxide (NaOH)
Produced by the Chlor-Alkali process. Electricity is passed through Brine (aq. NaCl).
B. Bleaching Powder (CaOCl2)
Used for disinfecting water and in the textile industry. Formed by action of Chlorine on Slaked Lime.
C. Baking Soda (NaHCO3)
Used for making crispy snacks and in fire extinguishers. It is a mild non-corrosive base.
D. Plaster of Paris (CaSO4.½H2O)
Obtained by heating Gypsum at 373 K. Used by doctors for supporting fractured bones.
End of Chapter Notes. Happy Learning!
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