Question

MALL HELE PRESE BE Mole fraction of KCl in a solution containing 10 g of it (i.e. KCI) (atomic mass of KCL = 74.5) in 100 g of water is

please help me calculate the mole fraction for this question!!

Answer 1

Answer:-

Given:-

wt. or mass of KCl = 10 g

molar mass of KCl = 74.5 g/ mol

wt. or mass of water (H₂O) = 100 g

mole fraction of KCl ($\chi$_KCl) = ?

As we know that

molar mass of water (H₂O) = 2 $\times$ molar mass of H + molar mass of O

molar mass of water (H₂O) = 2 $\times$ 1 +16

molar mass of water (H₂O) = 2 + 16

molar mass of water (H₂O) = 18 g/ mol

Also we know that

no. of moles of substance (n) = wt. or mass of substance / molar mass of substance

So

no. of moles of KCl in solution (n_KCl) = wt. or mass of KCl / molar mass of KCl

no. of moles of KCl in solution (n_KCl) = 10 g / 74.5 g/ mol

no. of moles of KCl in solution (n_KCl) = 0.1342 mol

similarly

no. of moles of water (H₂O) in solution (n_{H2O​​​​​​​}) = wt. or mass of water (H₂O) / molar mass of water (H₂O)

no. of moles of water (H₂O) in solution (n_{H2O​​​​​​​}) = 100 g / 18 g/ mol

no. of moles of water (H₂O) in solution (n_{H2O​​​​​​​}) = 5.5556 mol

So

total moles in the solution (n_total) = no. of moles of KCl (n_KCl) + no. of moles of water (H₂O) (n_{H2O​​​​​​​})

total moles in the solution (n_total) = 0.1342 mol + 5.5556 mol

total moles in the solution (n_total) = 5.6898‬ mol

therefore according to the formula

mole fraction of KCl ($\chi$_KCl) = no. of moles of KCl in solution (n_KCl) / total moles in the solution (n_total)

mole fraction of KCl ($\chi$_KCl) =  0.1342 mol /  5.6898‬ mol

mole fraction of KCl ($\chi$_KCl) = 0.0236 (i.e the answer)