Question

A solution was prepared by dissolving 155.0g of 245 g of water. Calculate the mole fraction of KCl(the formula weight of KCl is 74.6 g/mol. The formula weight of water is 18.0g/mol). Express the mole fraction of KClto two decimal places.

Answer 1

Given:-

weight of KCl = 155.0 g

molar mass of KCl = 74.6 g/mol

weight of water (H₂O) = 245 g

molar mass of water (H₂O) = 18.0 g/mol

mole fraction of KCl = ?

As we know that

no. of moles of KCl (n_KCl ) = weight of KCl / molar mass of KCl

no. of moles of KCl (n_KCl ) = 155.0 g/74.6 g/mol

no. of moles of KCl (n_KCl ) = 2.078

Similarly

no. of moles of water (H₂O) (n_H2O  ) = weight of water (H₂O) / molar mass of water (H₂O)

no. of moles of water (H₂O) (n_H2O  ) = 245.0 g/18.0 g/mol

no. of moles of water (H₂O) (n_H2O ) = 13.611

As we know that

mole fraction of KCl = no. of moles of KCl / total no. of moles present in solution

mole fraction of KCl =  n_KCl  / (n_KCl + n_H2O)

mole fraction of KCl = 2.078 / (2.078 + 13.611)

mole fraction of KCl =  2.078 / 15.689

mole fraction of KCl = 0.1324495 (i.e the answer)