Science, Tech, Math › Science What Is a Mole Fraction? Share Flipboard Email Print Arne Pastoor, Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated December 02, 2019 Mole fraction is a unit of concentration, defined to be equal to the number of moles of a component divided by the total number of moles of a solution. Because it is a ratio, mole fraction is a unitless expression. The mole fraction of all components of a solution, when added together, will equal 1. Mole Fraction Example In a solution of 1 mol benzene, 2 mol carbon tetrachloride, and 7 mol acetone, the mole fraction of the acetone is 0.7. This is determined by adding up the number of moles of acetone in the solution and dividing the value by the total number of moles of components of the solution: Number of Moles of Acetone: 7 moles Total Number of Moles in Solution = 1 moles (benzene) + 2 moles (carbon tetrachloride) + 7 moles (acetone)Total Number of Moles in Solution = 10 moles Mole Fraction of Acetone = moles acetone / total moles solutionMole Fraction of Acetone = 7/10Mole Fraction of Acetone = 0.7 Similarly, the mole fraction of benzene would be 1/10 or 0.1 and the mole fraction of carbon tetrachloride would be 2/10 or 0.2.