Question

A glass tube of volume 112ml. containing a
gas is partially evacuated till the pressure in it
drops to 3.8 x 10-5 torr at 0°C. The number of
molecules of the gas remaining in the tube is
1) 3 x 1017
2) 1.5 x 1014
3) 4.5 x 1018 4) 6 x 1018​

Answer 1

Answer:

1.5*10^14 atoms.

Explanation:  

Since, in the question it is given that the pressure in the glass tube after evacuation is 3.8*10^-5 torr which is 3.8*10^-5/760 atm and the R is 0.0821 L-atm/K mol. The volume of the glass tube is given as 112ml which is 0.112 L. So, using the formulae of PV=nRT. We will be able to to get the number of moles.

So, PV=nRT or 3.8*10^-5/760 * 0.112 = n*0.0821*273 which on solving we will get the value of n to be 2.49*10^-10. Since, for one mole there is 6.022*10^23. So, for 2.49*10^-10 mole we will have 6.022*10^23 * 2.49*10^-10 which will be 1.5*10^14 atoms.