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Question
Define Mole fraction.
Solution
The mole fraction of a component in a mixture is defined as the ratio of the number of moles of the component to the total number of moles of all the components in the mixture.
i.e.
Mole fraction of a component = `("Number of moles of the component")/("Total number of moles of all component")`
Mole fraction is denoted by ‘x’.
If in a binary solution, the number of moles of the solute and the solvent are nA and nB respectively, then the mole fraction of the solute in the solution is given by,
`"x"_"A" = "n"_"A"/("n"_"A"+"n"_"B")` .....(i)
Similarly, the mole fraction of the solvent in the solution is given
`"x"_"B" = "n"_"B"/("n"_"A"+"n"_"B")` .....(ii)
The sum of the mole fractions of all the components in a solution is always 1, i.e.
`"x"_"A" + "x"_"B" = "n"_"A"/("n"_"A" + "n"_"B") + "n"_"B"/("n"_"A" + "n"_"B")` = 1
Therefore, if the mole fraction of one component of a binary solution is known, then the mole fraction of the other component can be determined.
For example, for a binary solution, the mole fraction xA is related to xB in the following way:
xA = 1 – xB
or xB = 1 – xA
Mole fractions do not depend on the temperature of the solution.
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