the density of 3 molar solution of sodium chloride is 1.25gm/ml.calculate the molality of the solution
3M NaCl = 3moles/L soln.
3 moles = 3*58.5 g NaCl = about 180 mL but that's just approximately correct. You need to have a better answer than that.
Then 1 L of the soln has a mass of 1.25 g/mL x 1000 mL = 1250 g. How much of that is water. It is 1250 g -180 g NaCl = about 1070 g H2O.
Then m = moles/kg solvent.
To calculate the molality of a solution, we first need to understand the difference between molarity and molality.
Molarity (M) is defined as the number of moles of solute per liter of solution, while molality (m) is defined as the number of moles of solute per kilogram of solvent.
In this case, we have been given the density of the solution, which is 1.25 g/mL. However, first, we need to convert the density to grams per kilogram (g/kg) because molality requires the mass of the solvent in kilograms.
To convert density from grams per milliliter (g/mL) to grams per kilogram (g/kg), we can use the following conversion factor:
1 g/mL = 1000 g/kg
So, the density of the solution in g/kg is 1.25 * 1000 = 1250 g/kg.
Next, we need to know the molar mass of sodium chloride (NaCl), which is approximately 58.44 g/mol.
Now we can calculate the molality using the following formula:
Molality (m) = moles of solute / mass of solvent (in kg)
Since we have a 3 molar solution, it means that there are 3 moles of NaCl in 1 liter of the solution.
So the moles of solute in 1 liter (3 molar solution) are 3 moles.
To find the mass of the solvent, we need to use the density of the solution. From before, we know that the density is 1250 g/kg.
Assuming we have 1 liter of the solution, the mass of the solvent (in kg) can be calculated using the density and volume:
Mass of solvent (in kg) = volume of solution (in liters) * density
Mass of solvent (in kg) = 1 liter * 1250 g/kg
= 1250 g
Now we can calculate the molality:
Molality (m) = 3 moles / 1.250 kg
Therefore, the molality of the 3 molar solution of sodium chloride is approximately 2.4 mol/kg.