Question

# 0.727 g of an unknown metal is reacted with excess concentrated hydrochloric acid according to the...

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.

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)

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