25g of magnesium chloride (MgCl2) was dissolved in 250 ml distilled water at 25oC. The density of water was 0.9975g/cm3. Calculate the concentration in molality
m = mols/kg solvent
mols = g/molar mass = ?
mass solvent in g = volume x density. Then convert to kg.
Substitute into m = mols/kg solvent and that is m.
To calculate the concentration in molality (mol/kg), we need to determine the number of moles of magnesium chloride (MgCl2) dissolved in the solution and the mass of water in kilograms.
First, let's calculate the number of moles of MgCl2:
The molar mass of MgCl2 is:
Mg: 24.31 g/mol (atomic mass of magnesium)
Cl: 35.45 g/mol (atomic mass of chlorine)
MgCl2: 24.31 g/mol + 2 * 35.45 g/mol = 95.21 g/mol
Given that 25g of MgCl2 was dissolved, we can calculate the number of moles by dividing the mass by the molar mass:
Number of moles of MgCl2 = 25 g / 95.21 g/mol
Next, we need to determine the mass of water in kilograms:
Given that the density of water is 0.9975 g/cm³ and the volume of water is 250 ml, we can calculate the mass of water:
Mass of water = density * volume
= 0.9975 g/cm³ * 250 cm³
= 249.375 g
Converting the mass of water to kilograms:
Mass of water in kg = 249.375 g / 1000 = 0.249375 kg
Now we have the number of moles of MgCl2 and the mass of water in kilograms. We can calculate the molality (mol/kg) using the following formula:
Molality = moles of solute / mass of solvent (in kg)
Molality = Number of moles of MgCl2 / Mass of water in kg
Plug in the values:
Molality = (25 g / 95.21 g/mol) / 0.249375 kg
Molality ≈ 1.06 mol/kg
Therefore, the concentration of the MgCl2 solution is approximately 1.06 mol/kg.