Mole Fraction

Question

how is the mole fraction determined for different problems ? 

Answer 1

The mole fraction, often designated χ is the fraction of moles of interest over total moles.

 

Example:

0.10 mole of NaCl is dissolved into 100.0 grams of pure H₂O. What is the mole fraction of NaCl?

 

Find the total moles of H₂O + NaCl

 

100 g H2O * (1 mole / 18 g) = 5.56 mole water

 

Then, the mole fraction:

 

χ = (NaCl mol) / (NaCl mol + H2O mol)

 

χ = (0.1 mol) / (0.1 mol + 5.56 mol)

 

χ = 0.1 mol) / (5.66 mol) = 0.018

 

The mole fraction of H2O would then be

 

mol H₂O / total moles

 

5.56 mol / 5.66 mol = 0.982 mole fraction H₂O