5 g of a gaseous mixture of the He and Ar contained in a 10 l vessel at 27°C exert a pressure of 1 atm (absolute). Determine the mass percentage of He. Take R=112 Latm/molK
A
10.8
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B
14.2
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C
24.4
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D
74.6
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Solution
The correct option is C 24.4 Let the mass of He be x g, mass of Ar will be (5 - x) g Moles =massmolas mass Moles of He=x4 Moles of Ar=5−x40 Total moles of gas =x4+5−x40 PV=nRT⇒n=PVRT=1×101/12×300=0.4⇒x4+5−x40=0.4⇒x=1.22g Mass percentage of Helium = 1.225×100=24.4%,Ar=75.6%