Green chemistry examples in NCERT: which process replaced which (dry cleaning, bleaching, ethanal)? Mixing up the chemicals
Kavya NaikDropper Sample
15 Oct 2026 · 1 min read
Amma says I study chemistry like I'm doing a quiz show, fast but with mistakes 😅. Soil pollution and green chemistry is one of the "easy" last pages that I still get wrong in tests because the examples blur.
What I know: soil pollution comes from pesticides (insecticides, herbicides, fungicides) and industrial waste. DDT doesn't break down easily in soil and builds up in food chains. Green chemistry means designing processes that reduce or eliminate hazardous substances.
The part I mix up is the three NCERT examples: (a) dry cleaning of clothes (b) bleaching of paper (c) synthesis of ethanal (acetaldehyde)
Each had an "old way" and a "new way", and the old and new chemicals are: tetrachloroethene, chlorine, liquefied CO2, H2O2, and ethene. I know the five names but I can't pair them up correctly. In last week's test I put "chlorine" for dry cleaning, which was just embarrassing.
Please pair them for me, and tell me what's bad about the old methods. Also why is DDT such a persistent problem in soil, chemically? I only wrote "non-biodegradable".
6 answers & replies
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[+][–]Farhan ShaikhDropperSample· 5d ago
Quick pairing as I remember it:
- Dry cleaning: old = tetrachloroethene, new = liquid CO2 with a detergent
- Paper bleaching: old = chlorine, new = hydrogen peroxide
- Ethanal: ethene oxidised in one step
Wait, also liquefied CO2 replaces chlorine in the bleaching step, I think, because CO2 is "green"? Not sure.
[+][–]Zoya Khan12thSample· 4d ago
Farhan, the first and third are right, but liquid CO2 isn't used for bleaching. In bleaching of paper, chlorine used to be the bleaching agent and it produces chlorinated, toxic by-products. Now hydrogen peroxide (with a suitable catalyst) is used instead, and its by-product is just water. Liquefied CO2 appears only in dry cleaning.
Dry cleaning: tetrachloroethene was used as the solvent. It is a suspected carcinogen and contaminates ground water. Replaced by liquefied CO2 plus a suitable detergent, since CO2 is non-toxic and can be recycled.
[+][–]Kavya NaikDropperSample· 4d agoAuthor
ahh the pairing is finally clear, thank you zoya. "Chlorine only for the OLD paper bleaching" and CO2 for the clothes. Amma-approved 😄
[+][–]Siddharth RaoDropperSample· 4d ago
Ethanal: NCERT's example is that it used to be made by a longer multi-step route, and now ethene is oxidised to ethanal in a single step in aqueous medium in the presence of an ionic catalyst, with about 90% yield. Fewer steps, fewer by-products, less waste. That's the idea of "atom economy" and cutting steps.
If a question asks about the principle: green chemistry = prevent waste, use safer solvents, make processes efficient, and use renewable or less hazardous materials.
[+][–]Mehak AroraDropperSample· 4d ago
DDT: it's an organochlorine, a stable molecule. The C–Cl bonds and aromatic rings make it hard for soil microbes to break it down. It's also fat-soluble (non-polar) rather than water-soluble. So it doesn't wash away, it accumulates in fatty tissues of animals and gets more concentrated at each step up the food chain, which is biomagnification. That's one of the reasons it was banned or restricted in many places.
[+][–]Rahul DubeyDropperSample· 4d ago
In a test, write it as three one-liners:
- Dry cleaning: → liquid + detergent.
- Paper bleaching: → .
- Ethanal: multistep → ethene to ethanal, one step, ionic catalyst, aqueous, ~90%.
Soil pollution control: reduce pesticide use, use biodegradable ones, proper waste disposal, recycle, afforestation. Don't over-write, 2–3 lines are enough.
