The solubility of a compound with a molecular weight of 226.9 is determined to be 22.1 g in 125.0 g of water at 398 K. Express this concentration in terms of molality.

The correct answer is 0.78 m

Explanation:

Molality is defined as moles of solute per kilogram of solvent and it is expressed as mol/kg. In this case, the solute is the compound (with a molecular weight of 226.9) and the solvent is water.

First, we calculate the number of moles of compound we have in solution. For this, we divide the mass of compound into the molecular weight:

moles solute = 22.1 g x 1 mol/226.9 g = 0.097 mol

We have 0.097 moles of compound in 250 g of solvent (water) and we want to know the moles in 1000 g (1000 g = 1 kg):

0.097 mol x 1000 g/250g = 0.779 mol/kg = 0.078 m