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Polyhalogen Compounds: Uses and Environmental Concerns

Polyhalogen compounds are organic compounds containing more than one halogen atom. Important examples include chloroform, iodoform, freons, and DDT.

In one line: CHCl3 is chloroform, CHI3 is iodoform, CFCs affect ozone, and DDT persists.

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Understand it

  • Chloroform, iodoform, freons, and DDT are studied for their uses and risks.
  • Chloroform has historical solvent and anaesthetic relevance but is unsafe for such use.
  • Iodoform is recognized by its yellow solid formation in tests involving methyl ketones and ethanol-derived compounds.
  • Freons are chlorofluorocarbons linked to ozone layer depletion.
  • DDT is a chlorinated insecticide known for persistence and bioaccumulation concerns.

Example

Freon-12, CCl2F2, can release chlorine radicals in the upper atmosphere, which participate in ozone depletion cycles.

Rule to remember

Key examples: chloroform CHCl3, iodoform CHI3, freon-12 CCl2F2, DDT C14H9Cl5.

Environmental rule: stable chlorinated compounds may persist and accumulate, while CFCs can generate ozone-depleting chlorine radicals under ultraviolet light.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

Identify CCl2F2 and state its concern.

  1. 1CCl2F2 contains chlorine and fluorine atoms attached to carbon, so it is a chlorofluorocarbon called freon-12.
  2. 2Its environmental concern is ozone depletion through chlorine radical chemistry in the stratosphere.

Method you can reuse

Recognize the compound by formula or name, classify it as a polyhalogen compound, recall its common use, then attach the correct environmental or safety concern.

Visual tip

An environmental pathway diagram for CFCs and ozone depletion is helpful but should remain conceptual and school-safe.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why are CFCs considered environmentally harmful?

Think first, then show answer
CFCs can release chlorine radicals in the stratosphere, and these radicals catalyse ozone depletion.

Common wrong answer

Calling DDT biodegradable is wrong; its exam-relevant issue is persistence and accumulation through food chains.

Don't mix this up

Students often write that freons directly destroy ozone at ground level. The important concern is photochemical release of chlorine radicals in the stratosphere.

Exam tip

Learn one use and one harmful effect for each major polyhalogen compound; CBSE often tests balanced chemical awareness rather than only memorised names.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Questions commonly ask names, formulae, uses, environmental hazards, and short reasons for restricting compounds such as CFCs and DDT.
  1. 1

    Enough for 1 mark

    Polyhalogen compounds are organic compounds containing more than one halogen atom. Important examples include chloroform, iodoform, freons, and DDT.

  2. 2

    Add for 2 marks

    Example: Freon-12, CCl2F2, can release chlorine radicals in the upper atmosphere, which participate in ozone depletion cycles.

  3. 3

    Add for 3 marks

    Chloroform, iodoform, freons, and DDT are studied for their uses and risks.

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