A solution contains 25.5 g of NaCl dissolved in sufficient water to give a total mass of 325.0 g. What is the molality of the solution
no one knows?
mols NaCl = grams/molar mass
grams solvent = 325.0 - 25.5 = ?
Then m = mols NaCl/kg solvent.
To find the molality of a solution, we need to determine the moles of solute (NaCl) and the mass of the solvent (water).
First, let's calculate the moles of NaCl present in the solution:
Molar mass of NaCl = 22.99 g/mol + 35.45 g/mol = 58.44 g/mol
Moles of NaCl = mass of NaCl / molar mass of NaCl
Moles of NaCl = 25.5 g / 58.44 g/mol ≈ 0.437 mol
Since molality is defined as the moles of solute per kilogram of solvent, we need to convert the mass of water to kilograms:
Mass of water = total mass of solution - mass of NaCl
Mass of water = 325.0 g - 25.5 g = 299.5 g
Mass of water in kilograms = 299.5 g / 1000 g/kg = 0.2995 kg
Now, we can calculate the molality:
Molality = moles of NaCl / mass of water in kg
Molality = 0.437 mol / 0.2995 kg ≈ 1.46 mol/kg
Therefore, the molality of the solution is approximately 1.46 mol/kg.
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 approximately 58.5 g/mol.
Using the given mass of NaCl (25.5 g), we can calculate the moles of NaCl:
moles of NaCl = mass of NaCl / molar mass of NaCl
moles of NaCl = 25.5 g / 58.5 g/mol
2. Calculate the mass of the solvent (water):
The total mass of the solution (NaCl + water) is given as 325.0 g.
So, the mass of the solvent (water) can be calculated by subtracting the mass of NaCl from the total mass:
mass of solvent (water) = total mass - mass of solute
mass of solvent (water) = 325.0 g - 25.5 g
Now, we have all the information needed to calculate the molality.
3. Calculate the molality:
Molality (m) is defined as the number of moles of solute per kilogram of solvent.
To calculate the molality, we need to convert the mass of the solvent to kilograms:
mass of solvent (water) in kg = mass of solvent (water) / 1000
mass of solvent (water) in kg = (325.0 g - 25.5 g) / 1000
Finally, we can calculate the molality using the following formula:
molality = moles of solute / mass of solvent (in kg)
molality = (25.5 g / 58.5 g/mol) / (299.5 g / 1000)
Now, let's substitute the values and calculate the molality.
molality = (25.5 / 58.5) / (299.5 / 1000)