PHYSICAL CHEMISTRY IN BRIEF

CHAP. 1: BASIC TERMS [CONTENTS] 37

Example

A binary mixture contains 4 moles of substance A and 6 moles of substance B. Express the

composition of the mixture using mole fraction and mole percent.

Solution

According to (1.6), the amount of substance in the mixture isn= 4+6 = 10 mol. From (1.5)

we getxA= 4/10 = 0.4,xB= 6/10 = 0.6. The mixture contains 40 mole percent of substance

A, and 60 mole percent of substance B.

A mixture in which mole fractions of all components have the same value is called an

equimolar mixture.

Example

Calculate the mole fractions of an equimolar mixture of hydrogen and oxygen, and the mole

fractions of an equimolar mixture of nitrogen, oxygen and argon.

Solution

It follows from the definition of an equimolar mixture that

xH 2 =xO 2 =

1

2

and

xN 2 =xO 2 =xAr=

1

3

1.6.2 Mass fractionwi

Definition

wi=

mi

m

, (1.8)

wheremiis the mass of componenti, andm=

∑k
i=1miis the mass of the mixture.
U Main unit:dimensionless quantity.