A discharge tube containing nitrogen gas at `25^(@)C` in evacuated till the pressure is `2xx10^(-2)` mm. If the volume of discharge tube is 2 litre. Calculate the number of nitrogen molecules still present in the tube `(R=0*0821 L "atm mol"^(-1)K^(-1))`

Explanation

Step : 1 Calculation of number of moles of nitrogen.
Here `P=2xx10^(-2) mm =2xx10^(-2) xx(1)/(760) atm`
`V=2L, T=25^(@)C=298*15K`
According to ideal gas equation.
`PV=nRT:. N(PV)/(RT)=2xx10^(-2)(1)/(760)xx(2)/(0*821)xx(1)/(298*15)`
`:.n=2*15xx10^(-6)`
Step: 2 Calculation of number of molecules.
1 mol of nitrogen contains `=6*02xx10^(23)` molecules.
`2*15xx10^(-6)` mol of nitrogen contain `=6*02xx10^(23)xx2*15xx10^(-6)`
`1*29xx10^(18)` molecules