Q5. NCERT says world freon production was about 2 billion pounds a year by 1974. Express this in tonnes. (1 lb = 0.4536 kg; 1 tonne = 1000 kg.)
2 × 109 lb × 0.4536 kg/lb = 9.07 × 108 kg = 9.07 × 105 tonnes, nearly a million tonnes a year (NCERT page 188; reasoned).
Q6. A closed room holds 30 m3 of air. What volume of chloroform vapour would give the 900 parts per million that NCERT says can cause dizziness? (Take parts per million by volume.)
30 m3 × 900 × 10−6 = 0.027 m3, that is 27 L of vapour (reasoned from NCERT page 187).
Q7. Carbon tetrachloride was once a household fire extinguisher. Give two reasons from NCERT why it is no longer used so freely.
Any two: there is some evidence that it causes liver cancer; it causes dizziness, nausea and vomiting that can permanently damage nerve cells; it can make the heart beat irregularly or stop; released into the air, it depletes the ozone layer (NCERT page 187).
Q8. What does the name p,p’-dichlorodiphenyltrichloroethane tell you about where the five chlorine atoms of DDT are?
“Trichloroethane”: three Cl on the two-carbon ethane unit; NCERT’s structure (page 188) shows all three on one carbon, the CCl3 group. “Diphenyl”: two benzene rings, both on the other carbon. “p,p’-Dichloro”: one Cl on each ring, at the para position, opposite the ring’s bond to the ethane unit. The common name alone does not say which carbon carries which group; the structure does.