[quinnman]

Hello.
I have a mixture of 4 compounds. Each is given a mole fraction. How do I calculate the mole fraction of individual constituents of all the compounds?
Example:
Suppose that mixture consists of two compounds: LiF and BeF2, each has mole fraction 80% (LiF), respectively 20% (BeF2). Now, I want to calculate the mole fraction of Li in the mixture. What do I need for this?
Thank you.

[Yggdrasil]

Suppose you have 100 moles of your mixture.  How many moles of Li do you have in total?  How many moles of F do you have in total?  How many moles of Be do you have in total?  What is the total number of moles of atom in the mixture?

[quinnman]

Suppose you have 100 moles of your mixture.  How many moles of Li do you have in total?  How many moles of F do you have in total?  How many moles of Be do you have in total?  What is the total number of moles of atom in the mixture?

I would say following:
Li: 100 moles * 0.8 * 1 = 80 moles
Be: 100 * 0.2 * 1 = 20 moles
F: 100 * 0.8 * 1 + 100 * 0.2 * 2 = 120 moles

Mole fractions would be 0.3637 (Li), 0.0909 (Be) and 0.5454 (F). Is it correct?

[Yggdrasil]

Yup.  Good job.