Chemistry Class 12 NCERT Solutions: Chapter 2 Solutions Part 16

Q: 38. Benzene and toluene form ideal solution over the entire range of composition. The vapour pressure of pure benzene and toluene at Equation are Equation and Equation respectively. Calculate the mole fraction of benzene in vapour phase if Equation of benzene is mixed with Equation of toluene.

Answer:

Molar mass of benzene Equation

Equation

Molar mass of toluene Equation

Equation

Now, no. of moles present in 80 g of benzene Equation

And, no. of moles present in 100 g of toluene Equation

∴Mole fraction of benzene, Equation

And, mole fraction of toluene, Equation

It is given that vapour pressure of pure benzene, Equation

And, vapour pressure of pure toluene, Equation

Therefore, partial vapour pressure of benzene, Equation

Equation

Equation

And, partial vapour pressure of toluene, Equation

Equation

Equation

Hence, mole fraction of benzene in vapour phase is given by:

Equation

Equation

Equation

Equation

Equation

Q: 39. The air is a mixture of a number of gases. The major components are oxygen and nitrogen with approximate proportion of Equation is to Equation by volume at Equation . The water is in equilibrium with air at a pressure of 10 atm. At Equation K if the Henry's law constants for oxygen and nitrogen are Equation mm and Equation respectively, calculate the composition of these gases in water.

Answer:

Percentage of oxygen Equation in air Equation

Percentage of nitrogen Equation in air Equation

Also, it is given that water is in equilibrium with air at a total pressure of 10 atm, that is, Equation

Therefore,

Partial pressure of oxygen, Equation

Equation

Partial pressure of nitrogen, Equation

Equation

Now, according to Henry’s law:

Equation

For oxygen

Equation

Equation

Equation

Equation

For nitrogen:

Equation

Equation

Equation

Equation

Hence, the mole fractions of oxygen and nitrogen in water are 4 Equation respectively.

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