Question

2 mole of ethyl alcohol are present with 6 mole of water. The mole fraction of alcohol is :
a.) 0.5
b.) 0.75
c.) 0.15
d.) 0.25

Answer 1

Hint:. The mole fraction is defined as the number of molecules of a component present in a mixture of components. It can be calculated by dividing the moles of a component by the sum of moles of all components.
Mole fraction of component A = $\dfrac{{Moles{\text{ of component A}}}}{{Moles{\text{ of all components}}}}$

Complete step by step answer:
We know that mole fraction is the number of molecules of a component present in a mixture of components. It is a unit of concentration. The mass fraction is unitless quantity. It can be calculated by dividing the moles of a component by the sum of moles of all components.
Mole fraction of component A = $\dfrac{{Moles{\text{ of component A}}}}{{Moles{\text{ of all components}}}}$
We have components as -
Moles of Ethyl alcohol = 2 mole
Moles of water = 6 moles
So, the mole fraction of ethyl alcohol = $\dfrac{{Moles{\text{ of Ethyl alcohol}}}}{{Moles{\text{ of Ethyl alcohol + Moles of water}}}}$
Mole fraction of ethyl alcohol = $\dfrac{2}{{{\text{2 + 6}}}}$
Mole fraction of ethyl alcohol = $\dfrac{2}{8}$
Mole fraction of ethyl alcohol = 0.25 moles
So, the correct answer is “Option D”.

Note: The mole fraction is different from mass fraction. The mole fraction is the fraction of molecules present while mass fraction represents the mass distribution. Mole fraction is not dependent on the temperature. The sum of mass fraction of all components is equal to 1. It can not be zero or negative. It can also not be greater than 1.