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what is Mole Fraction?
In chemistry, mole fraction x (also, and more correctly, known as the amount fraction) is a way of expressing the composition of a mixture. The mole fraction of each component i is defined as its amount of substance ni divided by the total amount of substance in the system, n
xi def= ni/n

where

n = i sum of ni


The sum is over all components, including the solvent in the case of a chemical solution. As an example, if a mixture is obtained by dissolving 10 moles of sucrose in 90 moles of water, the mole fraction of sucrose in that mixture is 0.1.

The same value for the mole fraction ratio is obtained using the number of molecules of i, Ni, and the total number of molecules of all kinds, N, since

Ni = niNA

where NA is the Avogadro constant ? 6.022×1023 mol–1. By definition, the sum of the mole fractions equals one, a normalization property.

i sum of xi def = 1

If you have 2 moles of x and 8 moles of y, the mole fraction of x is 2/10 or 0.2 and the mole fraction of y is 8/10 or 0.8. Mole fractions have to add up to 1, just like %s have to add up to 100.


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