Question

Calculate the percentage of NO2 by weight in N2O4 (a dimer of NO2) which has a vapour density of 36.

a. 27.7

b. 67.7

c. 37.7

d. 25.7

Answer 1

Molecular mass of N2O4 and NO2 gas mixture = 2 x vapor density = 2 x 36 = 72

So, in 100 gm of sample , no. of moles of gas mixture = 100/72 = 1.38

Let, no. of moles of NO2 =n

Then no. of moles of N2O4 = 1.39-n

molar mass of NO2 = 14 + 2 x16 = 46

and molar mass of N2O4= 2x14 + 4x16 = 92

So, we get,

n x 46 + (1.39-n)x 92 = 100

or, n = 0.606

Hence, Composition of NO2 in every 100 gm of sample = 0.606 x 46 = 27.8 gm

So, %age of NO2 = 27.8 % ( near to 27.7 )

so, answer = a).27.7

Answer 2

anwe wile be 142.1 and 142.2