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?



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?


Let the volume of the round bottomed flask be V.

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


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



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.


Molar mass of dinitrogen

Now, molecule of contains 14 electrons.

Therefore, molecules of contains =14× 3.01× 1023


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


Avogadro number

Thus, time required

Hence, the time taken would be