Question

a sample of iron reacted with hydrochloric acid. the liberated hydrogen occupied 40.1ml when collected over water at 27degrees at a barometric pressure of 750 torr .what is the mass of the sample of iron (because of the collection of gas over water. the vapor pressure of the water must be subtracted from the barometric pressure to find the pressure of hydrogen gas.

Answer 1

calculate mole of H₂  librated

Use ideal gas equation for calculation of mole of gas

Ideal gas equation

PV = nRT             where, P = atm pressure= 750 torr -26.7(vapour pressure of water) =723.3 torr = 0.9517 atm,

V = volume in Liter = 40.1 ml = 0.0401 L

n = number of mole = ?

R = 0.08205L atm mol^-1 K^-1 =Proportionality constant = gas constant,

T = Temperature in K = 27⁰C = 273.15+ 27 = 300.15 K

We can write ideal gas equation

n = PV/RT

Substitute the value

n = (0.9517 0.0401)/(0.08205 300.15) = 0.0015496 mole

0.0015496 mole of H₂ librated

chemical reaction between iron and HCl is

Fe + HCl FeCl₂  + H₂

According to reaction 1 mole Fe produce 1 mole H₂ then 0.0015496 mole of H₂ produced from 0.0015496 mole of iron

molar mass of iron = 55.85 gm/mole then 0.0015496 mole of iron = 0.0015496 55.85 = 0.0865 gm of iron

mass of iron = 0.0865 gm