What is Mole fraction: Definition and 22 Discussions

In chemistry, the mole fraction or molar fraction (xi) 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:








{\displaystyle x_{i}={\frac {n_{i}}{n_{\mathrm {tot} }}}}
The sum of all the mole fractions is equal to 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.

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  1. il postino

    Chemistry Relationship between ppm and mole fraction

    Hi all! I have a question ... I have to calculate the partial pressure of O2 Ccan I calculate the mole fraction from the data of 1 ppm of O2? The total pressure is 760 torr Thank you!
  2. MathematicalPhysicist

    Chemistry How to Calculate Mole Fractions and Molar Volume in a Thermodynamic System?

    Homework Statement This question is problem 1.3.1 from Herbert Callen's textbook in Thermodynamics, second edition. In the answers I have the following: Mole fraction of NaCl = 0.057, molar volume =$18\times 10^{-6} m^3/mole$. How did they arrive at these answers? did they multiplied the...
  3. F

    Mass fraction to mole fraction

    How to convert mass fraction to mole fraction? Is it using the molecular weight?
  4. toforfiltum

    Chemistry Some problems with mole fraction

    Homework Statement Homework Equations not sure The Attempt at a Solution First, I'm a bit confused as to what the mole fraction of the products mean. Can someone explain? Is it something to do about the total number of carbon and hydrogen atoms in methane, ethene and propene? Just can't...
  5. mooncrater

    Chemistry Partial pressure vs mole fraction graph

    Homework Statement There is a statement in a book : " Graph of P vs ##\chi## is a straight line which ##cannot## pass through origin" Homework EquationsThe Attempt at a Solution But if mole fraction of a component is zero then it can't form vapours because of which its partial pressure will be...
  6. H

    Chemistry Mole fraction of gas in a mixture

    Homework Statement At 1 atm and 0° C, a 5.04 L mixture of methane (CH4) and propane(C3H8) was burned producing 20.9 g of CO2. Assume complete combustion. 1. How many moles total of methane and propane were present before combustion? 2. How many moles of carbon dioxide were present after the...
  7. S

    Feed Ratio and Mole fraction outut

    Homework Statement The chemical analysis of a fuel is determined to be: 84.60 wt% C, 11.12 wt% H, 1.95 wt % S and the balance, inerts. The fuel is consumed in a steam generating furnace with 33% excess theoretical air. The air is preheated to 190degreesC and enters the furnace at a gauge...
  8. K

    Chemistry Calculate Mole Fraction, Density, & %w/w given Molarity and Molality?

    Homework Statement Consider the following aqueous solution at 25°C Cr2(SO4)3, 1.26 mol/L, 1.37 mol/kg Calculate the mole fraction, density and % w/w Homework Equations χ = n Cr2(SO4)3 / n Cr2(SO4)3 + n H2O Unit conversions ρ= g solvent / mL solution % w/w = mass solvent / 100 g...
  9. J

    What is mole fraction solubility?

    As asked above, what is mole fraction solubility? From what I've been taught, it is the following equation: mole fraction solubility = (number of moles of solute)/(number of moles of solute + number of moles of solvent) Is that even correct? In actual fact, there's a question that deals with...
  10. G

    Chemistry Calculating Mole Fraction from Mass Fraction: Benzene-Toluene Mixture Example

    This is for my chemical engineering class...for some reason, I am struggling with this problem. I'm not quite sure how to connect the dots..I feel like I know how to do this, though. Homework Statement The mass fraction of benzene in a benzene-toluene mixture is 0.450. What is the mole...
  11. W

    Chemistry Finding mole fraction of polymers from weight percents %

    Watsup! I'm taking this nano class which is awesome but I am getting stuck on the gen chem material! no bueno. just want to make sure i did this right. Thanks! Homework Statement [/B] "A blend contains 45wt% polystyrene and 55wt% polypropylene. What is the mole fraction of polystyrene in the...
  12. S

    Mole Fraction of O2 to Mass of O2

    Hi Everyone, I am trying to calculate the mass of oxygen and keep running into dead ends and was wondering if anyone could offer any insight. I am trying to find the resulting mass of oxygen in a 6m x 6m x 6m enclosure at standard temperature and pressure when the mole fraction of oxygen...
  13. R

    Why is \frac{dN_i}{N}\neq dX_i when using the mole fraction concept?

    It looks like my first post on this did not make it on this forum some how. I came across this statement. Even though \frac{N_i}{N}=X_i, \frac{dN_i}{N}\neq dX_i How does this work? The book offered no help as well as searches on the internet.
  14. T

    Chemistry Calculating Molality and Mole Fraction for a 10% (by wt) Solution of KNO3

    Homework Statement A 10% (by wt) solution of KNO3 would have what molality and what mole fraction Homework Equations mole fraction = moles of KNO3/total moles wt % = # g of solute/total g molality = # moles KNO3/kg H2O The Attempt at a Solution 1 g KNO3/10 g total 1 g KNO3/101.1...
  15. S

    Coupling Raoult's & Antoine's Equations for Mole Fraction & Temp

    Homework Statement Given the equation for Roaults law and Antoine equation for 2 species I need to recast these into a pair of coupled non linear equations to compute the mole fraction of species one and the temperature for given values of vapor fraction and the total pressure, Antoines...
  16. D

    Chemistry Estimating Vapor Pressure and Vapor Mole Fraction

    1. Homework Statement The normal boiling points of benzene and toluene aer 80.1C and 110.6C, respectively. Both liquids obey Trouton's rule well. For a benzene-toluene liquid solution at 120C, with the molar fraction of benzene in the solution equalling 0.68, estimate the vapor pressure...
  17. A

    Chemistry Solve C2H2 Mol Fraction Problem: STP & Ideal Gas Eq.

    So I've been thinking about this problem for quite some time now any help will be appreciated. A sample of C_{2}H_{2}(g) has a pressure of 7.4 kPa. After some time a portion of it reacts to form {C}_6{H}_6 (g). The total pressure of the mixture of gases is then 3.6 kPa. Assume the volume and...
  18. M

    Chemistry Solving a Mole Fraction Problem with X & Y @ 250°C

    this problem should be simple, but i must be doing it wrong. At 250 degrees Celsius, a certain liquid X has a vapor pressure of 900 mm Hg and a second liquid Y has a pressure of 600 mm Hg. What is the minimum mole fraction of X necessary for the mixture to boil at this temperature (assume...
  19. S

    Chemistry Mole Fraction of 1.222 M Solution in Water - Help Needed

    Homework Statement can anyone help me with this problem...i can't seem to figure it out: A 1.222 M solution of a compound in water has a density of 1.3250g/mol at 20 degrees Celsius. what is the mole fraction of this solution? the compound has a molar mass of 97.80g/mol. Homework...
  20. S

    Chemistry Molar Mass of Unknown Solute and Mole Fraction of Gases

    1) Find the molar mass of an unknown substance if 227.5 mL of an aqueous solution containing 2.785 grams of the unknown generates an osmotic pressure of 588.0 mm Hg at 20.9 Celsius. Report your answer to 3 significant figures. pi = MRT pi = 588.0 mm Hg = 588 mm Hg/760 mm Hg = 0.7736842...
  21. Z

    Chemistry Help How to get the mole fraction ?

    An aqueous antifreeze solution is 37.0% ethylene glycol (C2H6O2) by mass. The density of the solution is 1.047 g/cm3. Q: Calculate the mole fraction of ethylene glycol. I tried it many time, but still got the wrong answer. that is what i did: mole fraction:(X) = nA/(nA+nB) set the...
  22. M

    Calculating Mole Fraction of C6H6(l) in Solution

    does anyone know how to do this problem? The total vapor pressure above a solution of C_6H_6(l) and C_7H_8(l) is 0.485 atm. What is the mole fraction of C_6H_6(l) in the liquid solution? P^o C6H6(l) = 0.526 atm P^o C7H8(l) = 0.188 atm the answer is 0.879 but I'm not sure how to get that...