What will be the mole fraction of ethanol in a sample of spirit containing 85% ethanol by mass ?
What will be the mole fraction of ethanol in a sample of spirit containing 85% ethanol by mass ?
A. `0.69`
B. `0.82`
C. `0.85`
D. `0.60`
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Correct Answer - A
`x_(C_2H_5OH)=(n_(C_2H_5OH))/(n_(C_2H_5OH)+n_(H_2O))`
Mass of `C_2H_5OH`=85 g
Molar mass of `C_2H_5OH`=46 g/mol
`n_(C_2H_5OH)=85/46`=1.85 mol
Mass of water =100-85 =15 g
`n_(H_2O)=15/18`=0.833 mol
`x_(C_2H_5OH)=1.85/(1.85+0.833)=1.85/2.683`=0.69
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