# Chemistry Class 11 NCERT Solutions: Chapter 5 States of Matter Part 4

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Q: 10. of phosphorus vapour weighs bar pressure. What is the molar mass of phosphorus?

Answer:

Given,

The number of moles (n) can be calculated using the ideal gas equation as:

Therefore, molar mass of phosphorus

Hence, the molar mass of phosphorus is

Q: 11. A student forgot to add the reaction mixture to the round bottomed flask at but instead he/she placed the flask on the flame. After a lapse of time, he realized his mistake, and using pyrometer, he found the temperature of the flask was. What fraction of air would have been expelled out?

Answer:

Let the volume of the round bottomed flask be V.

Then, the volume of air inside the flask at is .

Now,

According to Charles’s law,

Therefore, volume of air expelled out

Hence, fraction of air expelled out

Q: 12. Calculate the temperature of 4.0 mol of gas occupying

Answer

Given,

The temperature (T) can be calculated using the ideal gas equation as:

Hence, the required temperature is .

Q: 13. Calculate the total number of electrons present in of dinitrogen gas.

Answer:

Molar mass of dinitrogen

Now, molecule of contains 14 electrons.

Therefore, molecules of contains =14× 3.01× 10^{23}

electrons

Q: 14. How much time would it take to distribute one Avogadro number of wheat grains, if grains are distributed each second?

Answer:

Avogadro number

Thus, time required

Hence, the time taken would be