Mole fraction
- Mole fraction can be defined as the ratio of number of moles of the component in the solution to the total number of moles of all components in the solution.
- It is denoted by the alphabet x and subscript written on the right hand side of x denotes the component of which mole fraction is being calculated.
- Mathematically, Mole fraction of a component =
- Let us consider a binary mixture of A and B. let the number of moles of A and B bee nA and nB respectively, then
- For solution where number of components = i
- In a given solution sum of the mole fractions of all the components is unity. Mathematically, x1 + x2 + x3 …. + xi =1
Problem: Calculate the mole fraction of benzene in solution containing 30% by mass in carbon tetrachloride.
Solution:
Total mass of the solution = 100 g
Mass of benzene = 30 g.
∴ Mass of carbon tetrachloride = (100 - 30)g = 70 g
Molar mass of benzene (C6H6) = (6 × 12 + 6 × 1) g mol – 1 = 78 g mol - 1
∴ Number of moles of C6H6 =30/78 mol
= 0.3846 mol
Molar mass of carbon tetrachloride (CCl4) = 1 × 12 + 4 × 355 = 154 g mol - 1
∴ Number of moles of CCl4 = 70/154 mol = 0.4545 mol
Mole fraction of C6H6 =
