# Chemistry Class 11 NCERT Solutions: Chapter 5 States of Matter Part 2

Q: 4. At is same as that of dinitrogen at . What is the molecular mass of the oxide?

Answer:

Density (d) of the substance at temperature (T) can be given by the expression,

Now, density of oxide is given by,

Where, are the mass and pressure of the oxide respectively.

Density of dinitrogen gas is given by,

Where, are the mass and pressure of the oxide respectively.

According to the given question,

Given,

Molecular mass of nitrogen,

Now,

Hence, the molecular mass of the oxide is 70 g/mol.

Q: 5. Pressure of g of an ideal gas A at 27 is found to be . When of another ideal gas B is introduced in the same flask at same temperature the pressure becomes . Find a relationship between their molecular masses.

Answer:

For ideal gas A, the ideal gas equation is given by,

Where, represent the pressure and number of moles of gas A.

For ideal gas B, the ideal gas equation is given by,

Where, represent the pressure and number of moles of gas B.

[V and T are constants for gases A and B]

Form equation (i), we have

From equation (ii), we have

… … … (iv)

Where, the molecular masses of gases A and B respectively.

Now, from equations (iii) and (iv), we have

Given,

(Since total pressure is 3 bar)

Substituting these values in equation (v), we have

Thus, a relationship between the molecular masses of A and B is given by

.

Q: 6. The drain cleaner, Drainex contains small bits of aluminum which react with caustic soda to produce dihydrogen. What volume of dihydrogen at and one bar will be released when of aluminum reacts?

Answer:

The reaction of aluminium with caustic soda can be represented as:

At STP (273.15 K and 1 atm), 54 g (2× 27g) of Al given 3× 22400 mL of

At STP,

Let the volume of dihydrogen be atm (Since 1 bar = 0.987 atm) and

Now,

Therefore, 203 mL of dihydrogen will be released.