30cm3 of hydrogen was collected over water at 27°C and 780 mm Hg. If the vapour pressure of water at the temperature of the experiment was 10 mm Hg, calculate the volume of the gas at 760 mm Hg and 7°C?

  • A 40.0 cm3
  • B 35.7 cm3
  • C 28.4 cm3
  • D 25.2 cm3
jamb 1998chemistry

The correct answer is C. 28.4 cm3

Y1 = 30cm3 T1 = 27 + 273 = 300K and P1 = (780 - 10)mm Hg i.e the pressure minus the vapour pressure of water

P2 = 760mm Hg and T2 = 7 + 273 = 280K

From (P2V2) / (T2) = (P1V1) / (T1)

(770 x 30) / (300) = (760 x O2) / (280)

V2 = (770 x 30x 280) / (300 x 760)

V2 = 28.4 cm3

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