The Total solution for NCERT class 6-12
From a certainapparatus, the diffusion rate of hydrogen has an average value of 28.7 cm3 s-1.The diffusion of another gas under the same conditions is measured to have anaverage rate of 7.2 cm3 s-1. Identify the gas.
[Hint: Use Graham’s law ofdiffusion: R1/R2 = ( M2 /M1 )1/2, where R1 , R2 arediffusion rates of gases 1 and 2, and M1 and M2 their respective molecular masses. The law is asimple consequence of kinetic theory.]
Given
Rate of diffusion of hydrogen, R1 = 28.7 cm3s-1
Rate of diffusion of another gas, R2 = 7.2 cm3s-1
According to Graham’s Law of diffusion,
We have,
R1 /R2 = √M2 / M1
Where,
M1 isthe molecular mass of hydrogen = 2.020g
M2 isthe molecular mass of the unknown gas
Hence,
M2 =M1 (R1 / R2)2
= 2.02 (28.7 / 7.2)2
We get,
= 32.09 g
32 g is the molecular mass of oxygen.
Therefore, the unknown gas is oxygen.