Question

0.727 g of an unknown metal is reacted with excess concentrated hydrochloric acid according to the reaction below.  0.335 L of hydrogen gas was collected over water on a day when the temperature was 25.0 ^oC and the pressure was 0.98 atm. The vapor pressure of water at 25.0 ^oC is 23.8 torr. Report the partial pressure of hydrogen gas in atmospheres, the molar mass of the metal and the atomic symbol for the metal. The ideal gas law constant R = 0.0821 L*atm*K^-1mol^-1.

Answer 1

Total pressure= 0.98 atm and vapor pressure of water= 23.8 torr =23.8/760 atm =0.0313 atm =saturation pressure

Partial pressure of hydrogen= total pressure- saturation pressure of water vapor= 0.98-0.0313=0.9487 atm

partial pressure is the pressure exerted if the gas alone occupies entire volume

V=0.335L P= 0.9487 atm T= 25 deg.c =25+273.15= 298.15K R=0.0821L.atm/mole.K

n= moles of hydrogen= PV/RT= 0.9487*0.335/(0.0821*298.15) =0.0129 moles

The reaction of metal with HCl is M+ 2HCl ---> MCl2 + H2

1 mole of Hydrrogen is produced from 1 mole of metal and excess H2.

0.0129 moles of metal is hydrogen is produced ffrom 0.0129 moles of metal

Moles= mass/ Molecular weight

Molecular weight of metal= mass of metal /Moles of metal = 0.727/0.0129 =56

The metal is Fe (whose atomic weigh is 56)