Calculate the molality of a solution containing 12.5 g of ethylene glycol (C2H6O2) dissolved in 135 g of water.

Solution 99P :

Step 1:

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 :

Molality(m) =

Step 2:

Given :

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 :

= 135g

= 0.135 Kg.