Question

A 0.470 gram sample of a metal, M, reacts completely with sulfuric acid according to: M(s) +H₂SO₄(aq) -> MSO₄(aq) + H₂(g)

    A volume of 217 mL of hydrogen is collected over water; the water level in the collecting vessel is the same as the outside level. Atmospheric pressure is 756.0 Torr and the temperature is 25 °C. Calculate the molar mass of the metal.

Answer 1

M(s) +H₂SO₄(aq) -> MSO₄(aq) + H₂(g)

1 mole                                       1 mole

Hydrogen gas collected on water . in the collection of gas some water is vapourised.

water vapour pressure at 25C⁰ is 23.8 torr

total atmospheric pressure                  = Hydrogen gas pressure+ water vapour pressure

756 torr                                          = PH2      + 23.8

pressure of Hydrogen                    = 756-23.8 = 732.2 torr

P    = 732.2/760 = 0.963 atm

T   = 25C⁰ = 25+ 273                   = 298K

V = 217ml                                  = 0.217L

R = 0,0821lit-atm/mole-k

PV = nRT

n = PV/RT

= 0.963*0.217/0.0821*298

= 0.208971/24.4658 = 0.00854 moles

M(s) +H₂SO₄(aq) -> MSO₄(aq) + H₂(g)

1 mole of metal react with H2SO4 to gives 1 mole of H2

0.00854 moles metal react with H2SO4 to gives 0.00854 moles of H2

molar mass of metal = mass of metal/ no of moles of metal

                             = 0.470/0.00854 = 55gm of metal >>>> answer