A sample of ethane (C2H6) gas has the same mass as 1.5 ×1020 molecules of methane (CH4). How many C2H6 molecules does the sample of gas contain?

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1 Answers

Mass of 1 molecule of CH4 =  16g/ NA 

Mass of 1.5 ×1020 molecules of methane = ( 1.5 ×1020  × 16 / NA)  g

Mass of 1 molecule of C2H6 =  30 / NA g

Mass of molecules of C2H6 is =  1.5 ×10 20​×16/ NA g 

∴ Number of molecules of ethane = (1.5 X 1020 X 16 / NA) X NA / 30 = 0.8 X 1020 

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