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

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

Answer:

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

Equation

Now, density of oxide Equation is given by,

Equation

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

Density of dinitrogen gas Equation is given by,

Equation

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

According to the given question,

Equation

Equation

Given,

Equation

Equation

Molecular mass of nitrogen, Equation

Now, Equation

Equation

Equation

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

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

Answer:

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

Equation

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

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

Equation

Where, Equation 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

Equation Equation

From equation (ii), we have

Equation … … … (iv)

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

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

Equation

Given,

Equation

Equation

Equation

Equation

(Since total pressure is 3 bar)

Substituting these values in equation (v), we have

Equation

Equation

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

Equation .

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

Answer:

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

Equation

Equation Equation

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

Equation

At STP,

Equation

Equation

Equation

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

Now,

Equation

Equation

Equation

Equation

Equation

Therefore, 203 mL of dihydrogen will be released.

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