Question text What is the mole fraction of benzene in a benzene-toluene solution whose vapor pressure is 51 torr at 20°C?

Mole fraction for benzene is 0.683

Explanation:

We need to determine the colligative property about vapour pressure which formula is:

ΔP = P° . Xm

where P° is vapour pressure of pure solvent.

ΔP = Vapor pressure of pure solvent - Vapor pressure of solution

In this case, our solvent is benzene and the solute is toluene. For this colligative property vapour pressure of solution is lower than pure solvent.

P° of benzene at 20°C is 74.7 Torr

Xm is the value for the mole fraction of solute.

Let's replace data: 74.7 Torr - 51 Torr = 74.7 Torr . Xm

Xm = 0.317 → That's the mole fraction for toluene.

Then, mole fraction for benzene will be: 1 - 0.317 → 0.683

answer: atomic mass was originally used to arrange elements on the periodic table, but is no longer used to organize the modern version.

explanation:

originally atomic mass was used to arrange elements on the periodic table from left to right in a row. each column then shows similar properties of elements of a group.

in modern periodic table, the atoms are arranged in increasing atomic number. as atomic number represents the number of protons in an atom which is unique for every atom.