Polyhalogen Compounds - DDT Chloroform Iodoform - UNSOLVED PRACTICE SET
Chapter: Haloalkanes and Haloarenes | Topic: Polyhalogen Compounds DDT Chloroform Iodoform
POLYHALOGEN COMPOUNDS - DDT CHLOROFORM IODOFORM - UNSOLVED PRACTICE SET
Topic: Polyhalogen Compounds DDT Chloroform Iodoform
Multiple Choice Questions
Q1. Chloroform is prepared industrially by:
- Chlorination of methane
- The haloform reaction
- Reduction of carbon tetrachloride
- Heating ethanol with bleaching powder
Q2. Iodoform is a:
- Yellow crystalline solid with antiseptic properties
- Colourless liquid used as anaesthetic
- White powder used as pesticide
- Gas used in refrigeration
Q3. The iodoform test is given by compounds containing:
- CH₃CO– group or CH₃CH(OH)– group
- Only CH₃CO– group
- Only CH₃CH(OH)– group
- Any carbonyl group
Q4. DDT is:
- An organochlorine insecticide
- An antibiotic
- A refrigerant
- A plasticizer
Q5. Chloroform on prolonged exposure to air and light forms:
- Carbon tetrachloride
- Phosgene (COCl₂)
- Methylene chloride
- Carbon monoxide
Q6. Which of the following will NOT give iodoform test?
- Ethanol
- Acetone
- Acetaldehyde
- Formaldehyde
Short Answer Questions
Q7. How is chloroform prepared from ethanol? Write the reaction and mention the reagents used.
Q8. Why is chloroform stored in dark bottles filled to the brim? What happens if it is exposed to air and light?
Q9. What is the iodoform test? Write the reaction of ethanol with I₂ and NaOH.
Q10. Why has DDT been banned in many countries despite being an effective insecticide?
Q11. Write the structure of iodoform. Why is it used as an antiseptic?
Q12. Your grandmother uses a yellow ointment for minor cuts. What compound gives it the yellow colour? Write its formula and one use.
Long Answer Questions
Q13. (a) Describe the preparation of chloroform from ethanol.
(b) Why is chloroform no longer used as an anaesthetic?
(c) What precautions must be taken while storing chloroform?
(d) Write the reaction of chloroform with nitric acid. What is the product and what is its use?
Q14. (a) Describe the iodoform reaction. Which compounds give a positive iodoform test?
(b) Write the reaction of acetone with I₂/NaOH.
(c) Explain why iodoform is used as an antiseptic.
(d) A compound with molecular formula C₄H₈O gives a positive iodoform test. What are the possible structures? How would you distinguish between them?
Q15. (a) Describe the structure and uses of DDT.
(b) Why was DDT considered a miracle insecticide when it was first discovered?
(c) What are the environmental and health hazards of DDT?
(d) Why is DDT still used in some countries despite the ban?
(e) What are the alternatives to DDT for malaria control?
Numerical / Application-Based Problems
Q16. The preparation of iodoform from ethanol involves the following steps:
Step 1: CH₃CH₂OH + I₂ + NaOH → CH₃CHO + NaI + H₂O
Step 2: CH₃CHO + 3I₂ + 3NaOH → CI₃CHO + 3NaI + 3H₂O
Step 3: CI₃CHO + NaOH → CHI₃ + HCOONa
(a) Write the overall balanced equation for the formation of iodoform from ethanol.
(b) Calculate the mass of I₂ required to produce 25 g of iodoform (CHI₃, molar mass = 394 g/mol) from ethanol.
(c) If 11.5 g of ethanol (C₂H₅OH, molar mass = 46 g/mol) is used, what is the theoretical yield of iodoform?
(d) In practice, a student obtains 15.7 g of iodoform from 11.5 g of ethanol. Calculate the percentage yield.
(e) Why is the yield never 100% in this reaction? (Consider at least two reasons.)
Q17. The following data relates to the preparation and properties of polyhalogen compounds:
| Compound | Molecular Formula | Molar Mass (g/mol) | Density (g/mL) | Boiling Point (°C) | Use |
|---|---|---|---|---|---|
| CHCl₃ | ? | ? | 1.49 | 61.2 | Solvent, historically anaesthetic |
| CHI₃ | ? | ? | 4.00 | 218 (decomposes) | Antiseptic |
| CCl₄ | ? | ? | 1.59 | 76.7 | Fire extinguisher, solvent |
| DDT | C₁₄H₉Cl₅ | ? | - | 260 (decomposes) | Insecticide |
(a) Complete the table by filling in the molecular formula, molar mass, and density where missing.
(b) Calculate the percentage of chlorine by mass in DDT.
(c) A fire extinguisher contains 2 kg of CCl₄. Calculate the number of moles of CCl₄.
(d) Chloroform has a higher boiling point than expected for its molecular mass. Explain why. (Hint: Consider intermolecular forces.)
(e) Iodoform has a very high density (4.00 g/mL). Why is it so dense? Would it sink or float in water?
Q18. In a school science exhibition, students create a display on "Polyhalogen Compounds: Boon or Bane?"
(a) A student displays an old bottle of chloroform with a label warning about phosgene formation. Write the reaction showing how chloroform forms phosgene in air and light. Why is phosgene so dangerous?
(b) Another student demonstrates the iodoform test using ethanol and shows the yellow precipitate. She explains that this test was historically used to test for diabetes. Why? (Hint: What compound is present in the breath of diabetics?)
(c) A third student presents data on DDT: it saved an estimated 25 million lives from malaria between 1940 and 1970, but was banned in 1972 in the US. Create a timeline showing:
1940s: DDT discovered and used in WWII
1950s-60s: Widespread agricultural use
1962: Rachel Carson's "Silent Spring" published
1972: DDT banned in US
2001: Stockholm Convention restricts DDT
Present: Limited use for malaria control
(d) The students debate whether DDT should be used in India for malaria control. India has 4% of the world's malaria burden. Present arguments for and against DDT use, considering:
Human health (malaria deaths vs. DDT toxicity)
Environmental impact (bioaccumulation, bird egg thinning)
Economic factors (cost of alternatives)
Resistance (mosquitoes developing DDT resistance)
(e) The teacher asks: "If you were a policy maker in the Indian Ministry of Health, what integrated approach would you recommend for malaria control that minimizes DDT use?" Design a multi-pronged strategy.