Answer:
1.08 m is the molality of the solution.
Explanation:
1st step: Determine the mass of solvent.
13% by mass means that 13 g are contained in 100 g of solution.
Solution mass = Solute mass + solvent mass
100 g = 13 g + Solvent mass
Solvent mass = 100 g - 13 g → 87 g
Second Step: Let's determine the moles of our solute mass (mass / molar mass)
13 g / 138.2 g/mol = 0.094 moles
Third step: Replace the data to determine molality.
Molality are the moles of solute in 1kg of solvent (mol/kg)
Before this, we must convert the solvent mass to kg
87 g . 1kg / 1000 g = 0.087 kg
molality → 0.094 mol / 0.087 kg = 1.08 m