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

• Chemistry
• GreatEscapist
In summary, Homework Equations state that the mass fraction of benzene in a benzene-toluene mixture is 0.450. The mole fraction of toluene in the mixture is 0.550.
GreatEscapist
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 fraction of toluene in the mixture? Molecular weights of benzene and toluene are 78.11 and 92.12 respectively.

listed

## The Attempt at a Solution

Mass fraction of toluene is .550

Now, that is dimensionless, and I don't know how to get going from here. I know it's simple, but I've forgotten my general chemistry...
I was thinking I just multiply that mass fraction by the molecular weight of toluene, but then that's still in g/mol...then I thought about adding them, which would make more sense (since I have the mass fraction). I don't know though, because I don't have the exact chemical formula.

Any tips or steps would be greatly appreciated. Thank you.

well mass fraction is of benzene is mass_benzene/(mass_mixture)=.450

they give you the molecular weights of each component, and you can find the molecular weight of the mixture by just adding the molecular weights.

since the masses are in grams, and moelcular weight is in g/mol, if you divide the mass by molecular weight you get just moles. just make sure what you do to one side of the equation you do to the other.

And then just manipulate the equation the same way you did to get the mass fraction of toluene.Hope that helps

Puchinita5 said:
they give you the molecular weights of each component, and you can find the molecular weight of the mixture by just adding the molecular weights.

Huh? Doesn't make any sense to me.

GreatEscapist: assume 100g of the mixture.

Aha- I knew I forgot something simple. Thank you for the 100 g suggestion. I didn't know if assuming an amount of grams was a legal move.

Technically you should assume mass m and solve with symbols, you would find in the end m cancels out. But 100g is much faster and less cumbersome.

## What is a simple mole fraction?

A simple mole fraction is a unitless quantity that represents the ratio of the number of moles of one component to the total number of moles in a mixture.

## How do you calculate the mole fraction?

The mole fraction can be calculated by dividing the number of moles of the desired component by the total number of moles in the mixture.

## What is the significance of mole fraction?

Mole fraction is important in determining the concentration of a particular component in a mixture. It is also used in various thermodynamic calculations.

## Can the mole fraction exceed 1?

No, the mole fraction is always a value between 0 and 1. A value greater than 1 would imply that there are more moles of the desired component than the total number of moles in the mixture, which is not possible.

## How do you convert mole fraction to mass fraction?

To convert mole fraction to mass fraction, you need to know the molecular weights of all the components in the mixture. Then, multiply the mole fraction of each component by its molecular weight and divide by the total of all the component's molecular weights.

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