Posted by Tracy on .
Heyy, I have a quick question. I am doing binary systems, and I have a water/propanol system, and it says " 0.433 mole fraction propanol (71.7% propanol by weight)" does this mean that the mole fraction of water is 0.433 or propanol? Cause if propanol is 71.7% then wouldn't it be the bigger fraction, and if Xprop + Xwater = 1 then then other fraction would be 0.567 and wouldn't that be bigger?

Inorganic 
DrBob222,
If it says 0.433 mol fraction of propanol then that must be what it is. The mole fraction of water will be 1.000  0.433 = ??
Remember that propanol has a molar mass much larger than that of water and mol fraction is [mols Prop/(mols Prop + mols H2O)]. You might want to do a quick calculation, to satisfy your curiosity, that 71.7 g prop + 28.3 g water gives a mol fraction of 0.433.