Question

A mixture of NO2 and N2O4 has vapor density 38.3 at 300k what is no of moles of NO2 in 100g of mixture

Answer 1

the vapour density of a gas is the density of that gas relative to that of hydrogen gas.

therefore ,

vapour density = (density of NO2/N2O4 mixture)/( density of H2 gas )

vapour density= (mass of NO2/N2O4 mixture )/ (mass of H2)

vapour density=( molar mass of NO2/N2O4 mixture)/(molar mass of H2)

vapour density = (molar mass of NO2/N2O4)/2

molar mass of NO2/N2O4 mixture = vapour density × 2
= 76.6g mol^(-1)

Let the percentage of NO2 gas be X, the percentage of N2O4 gas be 1-X

X (molar mass of NO2 gas ) + (1-X)(molar mass of N2O4 )=76.6

X(46)+(1-X)(92)=76.6
X= 33.48%

mass of N2O4 in 100g of mixture = 33.48g

number of moles of NO2 gas = 33.48/46
= 0.728 mol.

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