Everyday Chemistry: Water, Air, Fuels and Materials

Air

• Oxygen supports burning and respiration; nitrogen is inert and is fixed by bacteria and lightning; CO2 is used by plants, in fire extinguishers, soda water and dry ice.
• Ozone (O3): in the stratosphere at 15 to 35 km; absorbs harmful UV rays. CFCs deplete it. Montreal Protocol (1987) controls this.
• Greenhouse gases: CO2, methane, water vapour, nitrous oxide, CFCs. Global warming results from their increase.
• Test for gases: CO2 turns lime water milky; hydrogen burns with a pop; oxygen relights a glowing splinter; ammonia has a pungent smell.

Water

• Formula H2O; two hydrogen atoms bonded to one oxygen. Pure water has no taste, colour or smell, and pH 7.
• Heavy water (D2O) is used as a moderator in nuclear reactors.
• Hard water forms scum with soap; soft water lathers easily.
• Water treatment: sedimentation, filtration, chlorination; ozone and UV are also used.
• Water pollution: industrial effluents, sewage, pesticides; eutrophication is excess nutrients causing algal bloom. BOD (biochemical oxygen demand) measures pollution by organic waste.

Combustion and fuels

• Combustion is burning in oxygen with heat and light. Conditions for burning: a fuel, oxygen (air) and ignition temperature. Fire is extinguished by removing any one: water (cools; not for oil or electrical fires), CO2 (cuts off oxygen; for electrical and oil fires), sand or blanket.
• Types of combustion: rapid (fire), spontaneous (white phosphorus), explosive (crackers).
• Flame zones: innermost (dark, unburnt vapour), middle (partial combustion, luminous), outermost (complete combustion, hottest, non-luminous). Goldsmiths use the outermost zone.
• Ignition temperature: the lowest temperature at which a substance catches fire.
• Coal: from buried plants over millions of years (carbonisation). Types: peat, lignite, bituminous, anthracite (best, highest carbon). Products: coke, coal tar, coal gas. Coal tar yields benzene, naphthalene, phenol, used for dyes, drugs, explosives, plastics, paints.
• Petroleum (rock oil) is refined by fractional distillation: petroleum gas (LPG), petrol, kerosene, diesel, lubricating oil, paraffin wax, bitumen. Petrol is the most volatile; bitumen is the least. Octane rating shows the quality of petrol.
• Natural gas: mainly methane; used as CNG and in fertiliser plants. LPG has a foul-smelling ethyl mercaptan added to detect leaks.
• Biofuels: ethanol and biodiesel (from jatropha and oils).

Materials

• Biodegradable materials decompose by microbes (paper, food); non-biodegradable ones (plastics, glass) do not. Use the 3 Rs: reduce, reuse, recycle.
• Fertilisers: urea (46% N, the highest nitrogen), NPK, DAP, superphosphate; pesticides include insecticides, fungicides, herbicides. DDT is banned for its persistence.
• Dyes, soaps, medicines: antibiotics (penicillin, found by Alexander Fleming, 1928), antipyretics (paracetamol), analgesics (aspirin), antacids, antiseptics (dettol, iodine tincture), disinfectants.
• Fire extinguishers: soda-acid (baking soda + sulphuric acid, produces CO2), foam, CO2.
• Preservation of food: salt, sugar, oil, vinegar, sodium benzoate, cold storage, pasteurisation (heating milk at 70 C for 15 to 30 seconds, by Louis Pasteur).
• Artificial sweeteners: saccharin, aspartame.
• LPG cylinders in India: 14.2 kg domestic.
• Tear gas is chloropicrin; laughing gas is nitrous oxide; marsh gas is methane; dry ice is solid CO2; quicksilver is mercury; vitamin C is ascorbic acid; bleaching powder is calcium oxychloride; rock salt is NaCl; Epsom salt is magnesium sulphate; Glauber's salt is sodium sulphate; chile saltpetre is NaNO3.