When hydrogen gas is collected by displacement of water, there is always water v

Question

When hydrogen gas is collected by displacement of water, there is always water vapor mixed with the gaseous hydrogen. The partial pressure exerted by water vapor is called its vapor pressure and its numerical value depends on the of the gaseous mixture. Look up the vapor pressure of water vapor at 20 degree C in Appendix G. Its vapor pressure is torr. If the pressure of a gas is 760 mm of water, its pressure is torr (mm of mercury). (the density of mercury is 13.6 g/mL). The equivalent weight of a metal is that weight of the metal that will liberate 1.008 g of hydrogen gas (H_2) from an acid. However, 1.008 g of hydrogen is mol = mL at STP. The equivalent weight of aluminum is 9.0 g. The number of mol of hydrogen gas produced by the reaction between 2.00 g of Al and an acid is mol. The volume of the liberated gas at STP is mL.

Explanation / Answer

4 . Temperature is the answer .
   At STP the partial pressure of water vapor will be around that of the collected hydrogen gas and
  at 100oC the water vapor will have the same partial pressure as the atmospheric pressure.

5. 17.5 torr

6. Use the equation P = gh
For the same pressure ,
   1h1 = 2h2 ; 1 / 2 = h2/h1
1 g/mL / 13.6 g/mL = h2 / 760 mm of water
   h2 = 55.8823 mm of Hg

7. molar mass of H2 = 1.008 g /mol
   moles = 1.008 g / 1.008 g/mol =1 mol
At STP 1 mol of gas occupies 22.4 lit or 22400 mL

8. 2 / 9 = 0.22 mol of hydrogen gas is produced by the reaction between 2 gm of Al and acid
   The liberated gas at STP will be (2/9 ) * 22400 mL = 4977.7 mL
  
       


     

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