Applications & Explore Online അലോഹങ്ങൾ

Hydrogen, carbon, nitrogen, oxygen and chlorine are part of every Kerala day: the pencil in your bag, the appam on the breakfast table, the puffed chips packet, the green gram in the paddy field after harvest, the oxygen cylinder in the hospital and the bleaching powder in the well after a flood. Every section below has a small animation, the chemistry at work and a sample exam question. Safety boxes cover the three dangerous ones – carbon monoxide, chlorine and hydrogen. The page ends with a hub of links to explore online.

1. Hydrogen fuel and hydrogen buses go further

calorific value · only water forms Hydrogen has the highest calorific value കലോറിക മൂല്യം in Fig 7.2 – 143 kJ/g, about three times petrol – and when it burns the only product is water: 2H₂ + O₂ → 2H₂O. That is why it is called a clean fuel and is used in rockets as liquid hydrogen. Several countries, and some Indian cities, are testing hydrogen buses: in a fuel cell hydrogen combines with oxygen from the air to give electricity, and the “exhaust” is water vapour. The textbook's limitations still apply: hydrogen burns explosively and is difficult to store and transport, so such buses carry it in very strong tanks under high pressure.

2. Pencils and dry cells: graphite at work

graphite: soft layers · free electrons The “lead” of a pencil contains no lead: it is graphite ഗ്രാഫൈറ്റ് mixed with clay. Graphite's layers are held by weak forces, so when you write, thin layers slide off and stay on the paper as a grey line. The same sliding layers make graphite a lubricant സ്നേഹകം. Each carbon in graphite has one free electron, so graphite conducts electricity: the black rod in the middle of an ordinary torch cell (dry cell) is a graphite electrode (the + terminal).

3. Diamond: jewellery and glass cutters

diamond: hard · high refractive index In diamond വജ്രം every carbon atom is bonded to four others in a strong 3-D network, so it is the hardest natural substance: a tiny diamond on a glass cutter scratches glass easily, and diamond-tipped tools cut and drill rock. Diamond also has a high refractive index അപവർത്തനാങ്കം, so light entering a well-cut diamond is bent strongly and reflected again and again inside before it comes out: it sparkles, which is why it is prized in jewellery. go further Its refractive index is about 2.42 (glass about 1.5).

4. Soda drinks and fire extinguishers: carbon dioxide

CO₂: no burning · denser than air · acidic in water Carbon dioxide does not burn and does not support burning, and it is denser than air. Poured over a fire, it sinks and covers the flame like a blanket, cutting off oxygen: that is how a CO₂ fire extinguisher അഗ്നിശമനികൾ works (look for the one in your school corridor). In soda water and soft drinks, CO₂ is dissolved under pressure; its solution is slightly acidic (carbonic acid കാർബോണിക് ആസിഡ്), which gives soda its sharp taste. Solid CO₂, dry ice ഡ്രൈ ഐസ്, makes the stage “smoke” at concerts.

5. Appam and cakes: baking soda അപ്പക്കാരം

bicarbonate → CO₂ Baking soda (appakkaaram, sodium bicarbonate, NaHCO₃) is a salt of carbonic acid. When batter containing it is heated, it gives off carbon dioxide; the gas bubbles get trapped in the batter and make the appam or cake soft and spongy. Do not confuse it with washing soda അലക്കുകാരം, Na₂CO₃·10H₂O, which is used for washing clothes, not for food. go further On heating: 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂. (Traditional kallappam batter can also rise by fermentation with yeast or toddy, which also makes CO₂.)

6. Carbon monoxide poisoning and safe ventilation

CO: poisonous · forms when oxygen is short When carbon burns with too little oxygen, carbon monoxide forms: 2C + O₂ → 2CO. It has no colour and no smell. CO combines with the haemoglobin in blood to form carboxyhaemoglobin കാർബോക്സീഹീമോഗ്ലോബിൻ, so the blood can carry less oxygen; headache, sleepiness and even death can follow. This is why a charcoal stove or a heater must never be burnt in a closed room, and why a car engine must never be left running in a closed garage.

7. Puffed chips packets and nitrogen in tyres

nitrogen is inert Nitrogen നൈട്രജൻ has a strong triple bond (N≡N), so it is inert നിഷ്ക്രിയം under ordinary conditions. Chips and snack packets are filled with nitrogen instead of air: there is no oxygen to react with the oil in the chips and spoil their taste, and the puffed packet cushions them so they do not break. Nitrogen is also used to fill vehicle tyres. go further Tyre shops say nitrogen keeps the pressure steadier and causes less rusting of the wheel rim than moist air.

8. Pulses in crop rotation: nitrogen fixation

nitrogen fixation Plants need nitrogen but cannot use N₂ from the air directly. Bacteria called Rhizobium, living in the root nodules of pulse plants such as green gram, black gram and cowpea (payar), convert atmospheric nitrogen into nitrogen compounds that plants can use: nitrogen fixation നൈട്രജൻ സ്ഥിരീകരണം. Many Kerala farmers grow a pulse crop in the paddy field after the harvest; when its roots and leaves are ploughed back, the next crop gets this nitrogen. This is crop rotation.

9. Organic manure or chemical fertiliser? Kerala farming

organic manure · chemical fertiliser In Kerala's paddy fields, coconut groves and vegetable gardens, farmers use both organic manure ജൈവവളം (cow dung, compost, green leaves, ash) and chemical fertilisers രാസവളം (urea, ammonium salts, phosphates, potash). Table 7.4 compares them: each has merits and limitations. Agricultural officers at the Krishi Bhavan usually advise a soil test and a combination: organic manure for soil health, and chemical fertiliser only in the amount the crop needs.

10. Hospital oxygen: the life gas പ്രാണവായു

oxygen supports life and burning Patients who cannot get enough oxygen from air are given oxygen from cylinders or a pipeline through a mask (artificial respiration). The gas passes through water in a humidifier bottle so that it does not dry the nose and throat. Carbogen കാർബൊജൻ – 95 % oxygen and 5 % carbon dioxide – is also used for artificial respiration. Oxygen is a strong supporter of combustion ജ്വലനസഹായി, so near oxygen, anything that catches fire burns far more fiercely.

11. Ozone Day and CFC-free refrigerators

ozone absorbs UV · CFCs destroy ozone High in the stratosphere, ozone (O₃) absorbs harmful ultraviolet radiations അൾട്രാവയലറ്റ് വികിരണങ്ങൾ from the Sun. Old refrigerators and air conditioners used CFCs ക്ലോറോഫ്ലൂറോകാർബണുകൾ (CFC); leaked CFCs reach the stratosphere, break up and release chlorine, which destroys ozone – ozone layer depletion ഓസോൺ പാളിയുടെ ശോഷണം. Today's “CFC-free” fridges use substitutes such as HFCs, hydrocarbons or ammonia. 16 September is International Ozone Day.

12. Bleaching powder for wells after floods

chlorine: disinfectant After the floods, Kerala's health department chlorinates thousands of wells with bleaching powder ബ്ലീച്ചിങ് പൗഡർ, Ca(OCl)₂. In water it releases chlorine compounds (HOCl), which kill disease germs such as those causing cholera and typhoid – chlorine is a disinfectant അണുനാശിനി. That is why well water smells of chlorine for a while after this “super-chlorination”. The amount and the waiting time before use are set by the health workers, so follow their instructions.

13. Chlorine in drinking-water treatment

chlorine kills germs Water from a river or reservoir is cleaned in steps at a treatment plant: big rubbish is screened out, mud settles in large tanks, and the water is filtered through sand. Filtering removes particles but not all germs, so a small, controlled amount of chlorine is added last, to kill the germs. A little chlorine remains in the water in the pipes and tanks, protecting it on the way to our homes. (Remember from Chapter 6: drinking water contains only a few ppm of chlorine.)

🌐 Explore online – resources hub

Everything in this guide works offline. The links below are extras: articles and simulations from trusted sources, grouped by topic. They need internet and open in a new tab, so you will not lose your place here. Ask a parent or teacher before you go online.

Hydrogen and fuels

Allotropes of carbon

Carbon dioxide and carbon monoxide

Nitrogen, its cycle and fertilisers

Oxygen, ozone and CFCs

Chlorine and bleaching powder

More to explore