First start by finding the mass of the gas mixture.
density = (mass )/ (volume)density=massvolume
mass = density xx volumemass=density×volume
mass = 19.92 \ g/L xx 5.00 \ L
mass = 19.92 \ g/cancel(L)xx 5.00 \ cancel(L)
mass = 99.6 \ g
The above mass is the mass of the gas mixture (m_(mix)). It includes the masses of N_2 , H_2 and CO.
color (red) (m_(mix) = m_(N_2) + m_(H_2) + m_(CO))
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underbrace(m_(N_2) = ???)
m_(H_2) = n_(H_2) xx MM_(H_2)
m_(H_2) = 3.55 \ mol. xx 2.016 \ g/(mol.)
m_(H_2) = 3.55 \ cancel(mol.)xx 2.016 \ g/(cancel(mol.))
underbrace(m_(H_2) = 7.16 \ g)
m_(CO) = n_(CO) xx MM_(CO)
m_(CO) = 1.25 \ mol. xx 28.01 g/(mol.)
m_(CO) = 1.25 \ cancel(mol.) xx 28.011 g/(cancel(mol.))
underbrace (m_(CO) = 35.0 \ g)
m_(N_2) = m_(mix) -{ m_(H_2) + m_(CO)}
m_(N_2) = 99.6 \ g - { 7.16 \ g +35.0 \ g}
underbrace (m_(N_2) = 57.4 \ g)
Once the mass of N_2 is determined, find the number of moles.
n_(N_2) = (m_(N_2))/ (MM_(N_2))
n_(N_2) = (57.4 \ g)/ (28.02 \ g.mol.^-1)
n_(N_2) = (57.4 \ cancel(g))/ (28.02 \ cancel(g).mol.^-1)
n_(N_2) = 2.05 \ mol.