KCET 2021 Chemistry Solved Paper

Given, Henry's law constant (KH) for the solubility of N2 gas in water at 298K=1×105‌atm.
Mole fraction of N2(χN2)=0.8
Hence, partial pressure of nitrogen,
pN2=ptotal.χN2
=0.8×5‌atm
=4‌atm
According to Henry's law,
pN2=KH χN2
4=105.χN2
χN2=4×10−5
We know that,
χN2=

nN2

nN2+nH2O

4×10−5=

nN2

10

(∵nN2<<<nH2O)
⇒ nN2=4×10−4 moles
Thus, the number of moles of N2 from air dissolved in 10 moles of water at 295K and 5‌atm pressure is 4×10−4.