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Mole fraction is the ratio of the number of moles of a substance to the total number of moles in a solution. One mole contains 6.02 x 10^23 molecules and has a mass in grams equal to the sum of the atomic masses of the atoms in the molecule. Mole fraction is useful for calculating the mass of each substance in a solution and determining the concentration of a solution.
Mole fraction is the total number of moles of a particular substance present in a sample, usually a solution, divided by the combined number of moles of all components in the same sample. If a solution contains 8 moles of total material and 3 moles of the total are carbon molecules, the mole fraction would be 0.375 when expressed as a decimal, which is more common than representing it as an actual fraction.
One mole is defined as the number of molecules in 12 grams of pure carbon-12. This number, also known as Avogadro’s number, is 6.02 x 1023. One mole of any substance contains the same number of molecules. This means that one mole of any substance has a mass of the combined atomic numbers of all atoms present in a molecule of that material, in grams. This is useful for writing chemical equations and for other calculations in chemistry.
To determine the mole fraction of any material in a solution, it is only necessary to know the number of moles of that particular component and the total number of moles of everything else in the solution. The number of moles of the other individual components is not necessary as long as the total number of moles is known. If the number of moles of each constituent is known, however, the mole fraction of each can also be found by dividing the number of moles of one by the number of moles of all constituents combined.
Finding the mole fraction of a particular constituent of a solution is useful for a variety of reasons. Using the mole definition, several other figures based on the mole fraction can be calculated. Applying knowledge of the mole definition and how it relates to the mass of a particular pure substance, if one knows the number of moles of each constituent of a solution, one can determine by simple calculations the mass of each substance, even if it dissolves in the solution. Molecular fractions are also used for many other things in chemistry, such as determining how much of a particular substance to dissolve in a solvent to make a solution of a particular concentration.
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