Answer:
2.21m
Step-by-step explanation:
Molality, m, is defined as the ratio between moles of solute (The substance that is in less amount, sodium sulfide) and kilograms of solvent (Water, in this case).
Thus, we need to convert mass of sodium sulfide to moles using its molar mass and grams of water to kilograms:
Moles Na2S (Molar mass: 78.0452g/mol):
37.5g * (1mol / 78.0452g) = 0.48 moles Na2S
Kilograms water:
217g * (1kg / 1000g) = 0.217kg
Molality:
0.48 moles Na2S / 0.217kg =
2.21m