a) 0.0400 mol of PH3 gas (MM=33.9976 g/mol) effuses through an orifice in 35 sec
ID: 526893 • Letter: A
Question
a) 0.0400 mol of PH3 gas (MM=33.9976 g/mol) effuses through an orifice in 35 seconds. How much nitrogen will effuse thru the same orifice in 35 seconds under identical conditions?
What is the ratio of the average speeds (urms) for xenon and argon at 298K? Setup ratio and calculate the ratio. Assume 3 sig figs.
b) A sample ammonia (MM=17.0304 g/mol) effuses through a pinhole in 35 seconds. An unknown gas takes 88 seconds to effuse under identical conditions. Calculate the molar mass of the unknown gas.
c) The unknown gas is possibly sulfur tetrafluoride, sulfur dioxide, or dihydrogen monosulfide. Which gas (or gases) is (are) probable? Show calculation or explain briefly
Explanation / Answer
from Grahms law of diffusion
rate of diffusion is inversly proportional to square root of molecular weight
rate of diffusion of NH3/ rate of diffsuion of N2= sqrt ( molar mass of N2/ molar mass of PH3)
0.04/35/ rate of diffsion of N2= sqrt(28/33.9976)
rate of diffusion of N2= (0.04/35)* sqrt( 33.9976/28)= 0.001259 mole/min
in 35 minutes. moles of N2 effused= 0.001259*35 moles =0.044 moles
2. urms= sqrt(3RT//M)
M= molar mass of gas
molar masses : Xe= 131, Ar = 40
urmsXe/urms Ar ( at the same temperature and pressrue)= sqrt(MAr/MXe)= Sqrt(40/131)= 0.5525
3. rNH3/runknown= sqrt( molar mass of unknown/molar mass of NH3)
rNH3= rate of effusion =moles of NH3 effused/ unit time
assuming 1 mole of NH3 effuses in 35 seconds. Same 1 mole effuses in 88 seconds
(1/35/1/88)= sqrt( M/17), M=108gm/mole
molar masses : SF4 = 108, SO2= 64 , H2S= 34 , Hence SF4 is the unknown gas
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