Soaps, Detergents and Polymers
NCERT Class 10 • Science • Chapter "Carbon and Its Compounds" | NCERT Class 8 • Science • Chapter "Synthetic Fibres and Plastics"
Soaps, Detergents and Polymers
Soap is the sodium or potassium salt of a long chain carboxylic acid. Its cleaning power comes from the fact that one end of the molecule is attracted to water and the other end to oil, so it can bridge two substances that otherwise refuse to mix.
How Cleaning Works
- A soap molecule has a hydrophilic head that dissolves in water and a hydrophobic tail that dissolves in oil and grease.
- When soap is added to dirty cloth, the tails attach to grease while the heads face the water.
- The molecules arrange themselves into a cluster called a micelle, which traps the dirt inside.
- Agitation lifts the micelles into the water and rinsing carries the dirt away.
- Hard water contains calcium and magnesium salts that react with soap to form an insoluble scum, which wastes soap and leaves deposits.
- Detergents are ammonium or sulphonate salts of long chain hydrocarbons; they do not form scum and work even in hard water.
- Detergents are therefore preferred for washing machines, but many are less easily broken down and can pollute water.
Polymers and Plastics
- A polymer is a very large molecule made by joining many small units called monomers.
- Natural polymers include cotton, silk, wool, rubber, starch, cellulose and protein.
- Synthetic polymers include nylon, polyester, acrylic, polythene, polyvinyl chloride and bakelite.
- Thermoplastics such as polythene and polyvinyl chloride soften on heating and can be remoulded.
- Thermosetting plastics such as bakelite and melamine do not soften once set, so bakelite is used in switches and melamine in fire resistant fabric and crockery.
- Plastics are light, durable, non reactive and cheap, which is exactly why they are so widely used and so hard to dispose of.
- Non biodegradable plastic waste is managed by the approach of reduce, reuse, recycle and recover.
| Feature | Soap | Detergent |
|---|---|---|
| Chemical nature | Salt of carboxylic acid | Salt of sulphonic acid |
| In hard water | Forms scum | Works well |
| Biodegradability | Generally biodegradable | Many are not |
Micelle — a spherical cluster of soap molecules with tails pointing inward towards the dirt and heads outward towards water.
Hindi me samjhein
साबुन के अणु का एक सिरा जल को पसंद करता है और दूसरा तेल को। यही दोहरा स्वभाव मैल को घेरकर मिसेल बनाता है और कपड़ा साफ कर देता है।
Exam me kaise aata hai
- The cluster of soap molecules around dirt is called a — micelle
- Soap forms scum in which kind of water — hard water
- Bakelite is which type of plastic — thermosetting
- Polythene is which type of plastic — thermoplastic
UPSC/State PSC ke liye
- Detergents work in hard water because their calcium and magnesium salts are soluble, unlike those of soap, so no scum forms.
- The very properties that make plastic useful, durability and non reactivity, are what make it an environmental problem when discarded.
Yahan confuse hote hain
✗ Soap works better than detergent in hard water | Detergent works better; soap forms scum | ✓
✗ All plastics can be remoulded on heating | Only thermoplastics can; thermosetting plastics cannot | ✓
✗ All polymers are synthetic | Cotton, silk, wool and rubber are natural polymers | ✓
Ek nazar me
- A soap molecule has a water loving head and an oil loving tail.
- Micelle formation traps dirt and lets water carry it away.
- Soap forms scum in hard water; detergent does not.
- Thermoplastics soften on heating; thermosetting plastics do not.