Calculate the molality of a solution containing 12.5 g of ethylene glycol (C2H6O2) dissolved in 135 g of water.
Solution 99P :
Here, we have to calculate the molality of each solution :
First, let’s see what is molality :
Molality(m) is a property of a solution and is defined as the number of moles of solute per kilogram of solvent. The SI unit for molality is mol/kg.
Formula to find the molality of solution :
Mass of solute - ethylene glycol (C2H6O2) = 12.5 g
Mass of solvent - water (H2O) = 135 g
We have solute in grams, we need moles of solute to calculate the molality. Hence, first we find the moles of solute from the grams given :
Number of moles(n) =
Molar mass of C2H6O2 = 62.07 g/mol
Therefore, n =
n = 0.201 moles
We need mass of solvent in Kg, to calculate molality, hence let’s convert mass of water in g to Kg :
1 kg = 1000 g
Therefore, 135 g of water in Kg will be :
= 0.135 Kg.