Acids, Bases and Salts
acids and bases neutralize each other.
Acid + Base → Salt + Water
- Acids taste sour and turn blue litmus red, while bases taste bitter and turn red litmus blue.
- acids release H⁺ ions while bases release OH⁻ ions in solution.
Indicators of Acids and Bases
- Substances like turmeric, litmus, red cabbage, beetroot and flower petals act as natural
- Synthetic indicators include phenolphthalein and methyl orange.
- Olfactory indicators (like vanilla and onion) change smell in acidic or basic conditions.
Acids and Bases interactions with metallic and non-metallic oxides
- Acids + Metals → Salt + Hydrogen gas (metallic oxides are basic in nature)
- Non-metallic Oxides + Bases → Salt + Water. Hence, non-metallic oxides are acidic in nature.
- Acids + Carbonates → CO₂ gas (turns lime water milky)
Acids and Bases interactions with water
- Only aqueous (water) solutions of acids and bases can conduct electricity.
- Acids react with water exothermically. The process must be done slowly with caution.
- Dilution decreases the concentration of H⁺ or OH⁻ ions per unit volume.
- All acids produce H⁺ ions (or H₃O⁺) in water. Bases produce OH⁻ ions in water. These ions are responsible for their acidic or basic properties.
pH Values of Substances
- Substances like lemon juice, tomato juice, and gastric juice are acidic.
- NaOH is strongly basic
Importance of pH in Everyday Life
- Plants and Animals: Survive within a narrow pH range (7.0 to 7.8).
- Acid Rain: Has pH < 5.6 and harms aquatic life.
- Soil pH: Affects plant growth. Ideal pH must be tested.
- Digestive System: Stomach acid helps digestion; antacids (like Milk of Magnesia) relieve acidity.
- Tooth Decay: Occurs if mouth pH < 5.5. Toothpaste (basic) helps prevent it.
- Chemical Defense: Bee stings and nettle stings are acidic (methanoic acid); baking soda neutralizes it.
- Creating a soda-acid fire extinguisher using sodium hydrogen carbonate and dilute sulfuric acid to produce CO₂, which extinguishes fire.
Naturally Occurring Acids
- Vinegar → Acetic acid
- Orange, Lemon → Citric acid
- Tamarind → Tartaric acid
- Tomato → Oxalic acid
- Ant sting, Nettle sting → Methanoic acid
- Curd → Lactic acid
Salts are formed from acids and bases, pH depends on strength of acid and base used:
- Strong acid + strong base → Neutral salt (pH ~ 7)
- Strong acid + weak base → Acidic salt (pH < 7)
- Weak acid + strong base → Basic salt (pH > 7)
Chemicals from Common Salt
- Sodium chloride (NaCl) is a neutral salt formed from HCl and NaOH. Rock salt is obtained from sea water or underground deposits (called brine).
Sodium Hydroxide (NaOH)
2NaCl(aq) + 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)
Bleaching Powder (Ca(OCl)₂)
Ca(OH)₂ + Cl₂ → Ca(OCl)₂ + CaCl₂ + H₂O
Uses: Bleaching cotton, paper, laundry. Disinfecting water. Oxidising agent.
Baking Soda (NaHCO₃)
NaCl + H₂O + CO₂ + NH₃ → NH₄Cl + NaHCO₃
2NaHCO₃ → Na₂CO₃ + H₂O + CO₂
Uses: Baking powder (with tartaric acid) for soft cakes. Antacid (relieves acidity). Fire extinguishers.
Washing Soda (Na₂CO₃·10H₂O)
Na₂CO₃ + 10H₂O → Na₂CO₃·10H₂O
- Made by recrystallizing sodium carbonate.
- Uses: Cleaning agent, glass/soap/paper industries. Removes hardness from water.
Crystals
- Crystals like CuSO₄·5H₂O contain water of crystallisation.
- On heating, water is lost, and colour fades (blue → white).
- Adding water restores original colour.
Plaster of Paris (POP), which is calcium sulfate hemihydrate (CaSO₄·½H₂O), used for setting fractured bones. When mixed with water, it reverts to gypsum (CaSO₄·2H₂O).
-
Made by heating gypsum (CaSO₄·2H₂O):
CaSO₄·2H₂O → CaSO₄·½H₂O + 1½H₂O
Used for plastering, making casts, and decorative materials.
Related Links
- General Science : Questions for Competitive Exams 🔗
General Science, Study Materials, Current Affairs, Practice Questions,