Everyday Chemistry & Gases

🎯 Learning Objective

Learn the chemical names of common household substances and the key facts about everyday gases and the air we breathe.

💡 Concept

• LPG (cooking gas) = Liquefied Petroleum Gas, mainly Butane (C₄H₁₀) and Propane (C₃H₈); CNG = Compressed Natural Gas, mainly Methane
• Common salt = Sodium chloride (NaCl); Baking soda = Sodium bicarbonate; Washing soda = Sodium carbonate
• Chalk / limestone / marble = Calcium carbonate (CaCO₃); Quick lime = Calcium oxide (CaO); Slaked lime = Calcium hydroxide, Ca(OH)₂
• Plaster of Paris = Calcium sulphate hemihydrate (CaSO₄·½H₂O); Blue vitriol = Copper sulphate (CuSO₄·5H₂O)
• Vinegar = dilute Acetic acid; Dry ice = solid Carbon dioxide; Laughing gas = Nitrous oxide (N₂O); Marsh gas = Methane (CH₄)
• Air composition: Nitrogen ~78%, Oxygen ~21%, Argon ~0.9%, Carbon dioxide ~0.04%
• Oxygen supports combustion and respiration; Carbon dioxide turns lime water milky and is used in fire extinguishers
• Carbon monoxide (CO) is a poisonous gas from incomplete combustion; Ozone (O₃) shields Earth from the Sun's UV rays
• Hydrogen is the lightest gas and is highly inflammable; Nitrogen is largely inert and used to make fertilizers
• Rusting of iron needs both oxygen and water; it is prevented by painting, oiling or galvanising (zinc coating)

🧮 Key Formulas

LPG = Butane (C₄H₁₀) + Propane (C₃H₈); CNG = Methane (CH₄)

>

Air: N₂ ~78% · O₂ ~21% · Ar ~0.9% · CO₂ ~0.04%

>

Dry ice = solid CO₂ · Laughing gas = N₂O · Marsh gas = CH₄

✏️ Easy Example

Q. The main gases present in LPG (cooking gas) are: (a) Methane and Ethane (b) Butane and Propane (c) Hydrogen and Oxygen (d) Nitrogen and Argon

1. LPG = Liquefied Petroleum Gas
2. Its main components are butane and propane

Answer: (b) Butane and Propane

🇮🇳 Real-Life Example

The 'dry ice' fog you see at weddings and stage shows is just solid carbon dioxide — no water involved. It turns straight from solid to gas (sublimation), which is why it smokes without ever becoming wet.

📝 Exam-Level Example

Q. The chemical name of the 'laughing gas' is: (a) Carbon dioxide (b) Nitrous oxide (c) Nitrogen dioxide (d) Methane

1. Laughing gas is used as a mild anaesthetic
2. It is nitrous oxide, N₂O

Answer: (b) Nitrous oxide (N₂O)

📝 Exam-Level Example

Q. The gas that turns lime water milky is: (a) Oxygen (b) Hydrogen (c) Carbon dioxide (d) Nitrogen

1. This is the classic test for one gas
2. Carbon dioxide turns lime water milky

Answer: (c) Carbon dioxide

🪄 Memory Trick

LPG = 'Bharat's Petroleum' → Butane + Propane. Air is mostly 'N then O': Nitrogen 78, Oxygen 21. Dry ice is 'dry' because it's CO₂ (no water) that sublimes.

⚠️ Common Mistakes

• ❌ Saying air is mostly oxygen — it's ~78% nitrogen, only ~21% oxygen
• ❌ Confusing LPG (butane/propane) with CNG (methane)
• ❌ Thinking dry ice is frozen water — it is solid carbon dioxide

🏆 Exam Tips

• ✅ Group the 'lime' family: quick lime CaO, slaked lime Ca(OH)₂, limestone CaCO₃
• ✅ Remember two air numbers — N₂ ~78%, O₂ ~21% — they anchor many questions

📌 Summary

• LPG = butane + propane; CNG = methane
• Common names: salt NaCl, baking soda NaHCO₃, limestone CaCO₃, dry ice = solid CO₂
• Air: ~78% nitrogen, ~21% oxygen
• CO₂ turns lime water milky; CO is poisonous; O₃ blocks UV