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JAMB Chemistry 1986 Question 6

Question 6

Gas Laws

200 cm3 of oxygen diffuse through a porous plug in 50 seconds. How long will 80 cm3 of methane (CH4) take to diffuse through the same porous plug under the same conditions? [C = 12, O = 16, H = 1].

  1. A.40 sec
  2. B.20 sec
  3. C.14 sec
  4. D.7 sec.
Show the answer and explanation

Answer: C (14 sec)

Explanation

Oxygen's rate is 200/50 = 4 cm3/s. By Graham's law methane is √(32/16) = 1.414 times faster, about 5.66 cm3/s, so 80 cm3 takes 80/5.66 ≈ 14 s.