Chemistry in Everyday Life
NCERT Class 8 • Science • Chapter "Combustion and Flame" | NCERT Class 8 • Science • Chapter "Coal and Petroleum"
Chemistry in Everyday Life
Chemistry is not confined to the laboratory. The fuel in a kitchen, the fertiliser on a field, the tablet in a medicine strip and the preservative in a packet of food all work on chemical principles, and the exam asks about exactly these familiar things.
Fuels and Combustion
- Combustion is a chemical process in which a substance reacts with oxygen to release heat and usually light.
- The lowest temperature at which a substance catches fire is its ignition temperature.
- A good fuel has high calorific value, a moderate ignition temperature, low ash and smoke, and is easily available and affordable.
- Calorific value is the heat produced by burning one kilogram of a fuel completely.
- Hydrogen has the highest calorific value among fuels, while coal, petroleum and natural gas are the common fossil fuels.
- The blue zone of a candle flame is the hottest, the yellow zone is luminous due to unburnt carbon, and the dark inner zone is coolest.
- Water is not used on oil or electrical fires; carbon dioxide is used instead because it cuts off oxygen and does not conduct.
Fertilisers, Medicines and Additives
- Fertilisers supply nitrogen, phosphorus and potassium to the soil; urea, ammonium sulphate and superphosphate are common ones.
- Overuse of fertiliser damages soil and washes into water bodies, causing excessive growth of algae.
- Pesticides protect crops but leave residues, so their safe limits matter.
- Antibiotics fight bacterial infection, analgesics relieve pain, antipyretics reduce fever and antacids neutralise stomach acid.
- Antiseptics are applied to living tissue while disinfectants are used on surfaces and objects.
- Food additives include preservatives, antioxidants, flavouring agents and colouring agents.
- Common salt, sugar, vinegar and oil are the traditional preservatives used in Indian homes.
| Substance | Function |
|---|---|
| Antibiotic | Fights bacterial infection |
| Analgesic | Relieves pain |
| Antacid | Neutralises excess stomach acid |
| Antiseptic | Applied on living tissue to stop infection |
Calorific value — the amount of heat produced by the complete burning of one kilogram of a fuel.
Exam me kaise aata hai
- The lowest temperature at which a fuel catches fire is its — ignition temperature
- Which fuel has the highest calorific value — hydrogen
- Which zone of a candle flame is hottest — the blue zone
- Medicines that reduce fever are called — antipyretics
UPSC/State PSC ke liye
- Carbon dioxide is used on electrical fires because it is non conducting and heavier than air, so it forms a blanket that cuts off oxygen.
- Excess fertiliser causes eutrophication, where algae grow rapidly, then decay and consume the oxygen that fish need.
Yahan confuse hote hain
✗ Water can be used on all fires | Water must not be used on oil or electrical fires | ✓
✗ The yellow zone of a flame is hottest | The blue zone is hottest | ✓
✗ Antiseptic and disinfectant are the same | Antiseptic is for living tissue; disinfectant for surfaces | ✓
Ek nazar me
- Combustion needs fuel, oxygen and ignition temperature.
- A good fuel has high calorific value and low ash and smoke.
- Fertilisers supply nitrogen, phosphorus and potassium but harm soil and water in excess.
- Antibiotic, analgesic, antipyretic and antacid each have a distinct role.
Ab practice karein
Carbon compounds aur daily life chemistry se seedhe questions bante hain. ExamAtlas ke mock test se abhi jaanchein.