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Answer» What is Mole Fraction mean? In chemistry, the mole fraction or molar fraction (xi or χi) is defined as unit of the amount of a constituent (expressed in moles), ni , divided by the total amount of all constituents in a mixture (also expressed in moles), ntot. This expression is given below: x i = n i n t o t {\displaystyle x_{i}={\frac {n_{i}}{n_{\mathrm {tot} }}}} The sum of all the mole fractions is equal to 1: ∑ i = 1 N n i = n t o t ; ∑ i = 1 N x i = 1. {\displaystyle \sum _{i=1}^{N}n_{i}=n_{\mathrm {tot} };\ \sum _{i=1}^{N}x_{i}=1.} The same concept expressed with a denominator of 100 is the mole percent, molar percentage or molar proportion (mol%). The mole fraction is also called the amount fraction. It is identical to the number fraction, which is defined as the number of molecules of a constituent Ni divided by the total number of all molecules Ntot. The mole fraction is sometimes denoted by the lowercase Greek letter χ (chi) instead of a Roman x. For mixtures of gases, IUPAC recommends the letter y. The National Institute of Standards and Technology of the United States prefers the term amount-of-substance fraction over mole fraction because it does not contain the name of the unit mole. Whereas mole fraction is a ratio of moles to moles, molar concentration is a quotient of moles to volume. The mole fraction is one way of expressing the composition of a mixture with a dimensionless quantity; mass fraction (percentage by weight, wt%) and volume fraction (percentage by volume, vol%) are others. reference
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