What is the molality of a solution composed
of 11.1 g NaCl dissolved in 638 g of water?
Answer in units of m.
m = mols/kg solvent
moles NaCl = grams/molar mass = ??
kg solvent = 0.638 kg H2O.
Substitute and solve for m.
To find the molality of a solution, we need to determine the number of moles of solute (NaCl) and the mass of the solvent (water).
1. Calculate the number of moles of NaCl:
- The molar mass of NaCl is 22.99 g/mol (sodium) + 35.45 g/mol (chlorine) = 58.44 g/mol.
- Divide the mass of NaCl (11.1 g) by its molar mass to get the number of moles: 11.1 g / 58.44 g/mol ≈ 0.190 mol.
2. Calculate the mass of the solvent water:
- The mass of water is given as 638 g.
3. Calculate the molality using the formula:
Molality (m) = moles of solute / mass of solvent in kg.
- Convert the mass of water to kilograms: 638 g / 1000 g/kg = 0.638 kg.
- Divide the number of moles of NaCl (0.190 mol) by the mass of water in kg (0.638 kg) to get the molality: 0.190 mol / 0.638 kg ≈ 0.298 m (round to three decimal places).
Therefore, the molality of the solution composed of 11.1 g NaCl dissolved in 638 g of water is approximately 0.298 m.