Answer
Mole fraction of ethanol: $0.089$
Mole fraction of water: $0.911$
Work Step by Step
For Ethanol ( C2H5OH) :
$mass=20g$
$molarmass=2\times12.011+5\times1.008+15.99+1.008$
$molarmass=46.069gram/mole$
number of moles of ethanol = Given mass ÷ molar mass.
$n_1=20\div46.069$
$n_1=0.434$
For water :
$mass=80g$
$molarmass=2\times1.008+15.99$
$molarmass=18.01gram/mole$
number of moles of ethanol = Given mass ÷ molar mass.
$n_2=80\div18.01$
$n_2=4.44$
Mole fraction of any substance is defined as ratio of moles of that substance to the sum of moles of all substances.
Mole fraction of ethanol:
Mole fraction of ethanol = moles of ethanol ÷ ( moles of ethanol + moles of water)
mole fraction of ethanol = 0.434 ÷ (0.434 + 4.44)
mole fraction of ethanol $=0.089$
Mole fraction of water= $1-$ mole fraction of ethanol
Mole fraction of water= $1-0.089$
Mole fraction of water$=0.911$
