Chemistry Class 11 NCERT Solutions: Chapter 5 States of Matter Part 6

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Q: 18. 2.9 g of a gas at 95 ° C occupied the same volume as 0.184 g of dihydrogen at 17 °C, at the same pressure. What is the molar mass of the gas?


Volume (V) occupied by dihydrogen is given by,

Let M be the molar of the unknown gas. Volume (V) occupied by the unknown gas can be calculated as:

According to the question,

Hence, the molar mass of the gas is .

Q: 19. A mixtures of dihydrogen and Dioxygen at one bar pressure contain by weight of dihydrogen. Calculate the partial pressure of dihydrogen.


Let the weight of dihydrogen be 20 g and the weight of Dioxygen be 80 g.

Then, the number of moles of dihydrogen, and the number of moles

Of Dioxygen,


Total pressure of the mixture,

Then, partial pressure of dihydrogen,

Hence, the partial pressure of dihydrogen is

Q: 20. What would be the SI unit for the quantity


The SI unit for pressure, p is


The SI unit for the number of moles is mol.

Therefore, the SI unit for quantity is given by,

Q: 21. In terms of Charles’ law explain why is the lowest possible temperature.


Charles’ law states that constant pressure, the volume of a fixed mass of gas is directly proportional to its absolute temperature.

It was found that for all gases (at any given pressure), the plots of volume vs. temperature (in is a straight line. If this line is extended to zero volume, then it intersects the temperature-axis at . In other words, the volume of any gas at is zero. This is because all gases get liquefied before reaching a temperature of . Hence, it can be concluded that is the lowest possible temperature.

Q: 22. Critical temperature for carbon dioxide and methane are and respectively. Which of these has stronger intermolecular forces and why?


Higher is the critical temperature of a gas, easier is its liquefaction. This means that the intermolecular forces of attraction between the molecules of a gas are directly proportional to its critical temperature; Hence, intermolecular forces of attraction are stronger in the case of .