A sample of hydrogen was prepared and collected over water at25 °C and a total p

Question

A sample of hydrogen was prepared and collected over water at25 °C and a total pressure of 742 torr. It occupied a volume of288 mL. The partial pressure of hydrogen is ________ torr. Under a pressure of 1 atm the dry volume of the hydrogen wouldbe _______ mL. A sample of hydrogen was prepared and collected over water at25 °C and a total pressure of 742 torr. It occupied a volume of288 mL. The partial pressure of hydrogen is ________ torr. Under a pressure of 1 atm the dry volume of the hydrogen wouldbe _______ mL.

Explanation / Answer

Total pressure = partial pressureof hydrogen gas + vapor pressure of water at 25°C From standard data: vaopor pressure of water at 25°C is 23.76torr So 742 torr = partial pressureof hydrogen gas   +23.76torr partial pressureof hydrogen gas   = 742torr - 23.76torr =718.24torr Moles of H2 gas = PH2 V / RT                           ={ (718.24torr (1atm / 760torr))* (288mL (1L /1000mL)) } / { (0.0821Latm mol^-1 K^-1)(25+273)K}                         = 0.0111 mol From: PV = nRT            V = nRT / P So V dyr gas = n drygas RT /P                     = (0.0111mol)(0.0821Latm mol^-1 K^-1)(298K) / 1atm                     = 0.27157L                     = 271. 57mL

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