Calculate the boiling point
a. 10.5 g FeCl3 in 2.11 102 g water
b.4.6% KCl by mass (in water)
c.0.140 m MgF2
The first one is done this way.
mols FeCl3 = 10.5/molar mass
molality = mols/kg solvent
delta T = i*Kb*m
Add delta T to 100 for new boiling point.
i = 4 for FeCl3, 2 for KCl and 3 for MgF2.
To calculate the boiling point, we need to determine the molality (m), which is the number of moles of solute per kilogram of solvent. Once we have the molality, we can use a boiling point elevation constant (Kb) specific to the solvent and plug it into the equation:
ΔTb = Kb * m
a. 10.5 g FeCl3 in 2.11 × 102 g water
First, we need to convert the mass of FeCl3 to moles. Using its molar mass, which is 162.2 g/mol:
moles of FeCl3 = 10.5 g / 162.2 g/mol = 0.0647 mol
Next, we need to calculate the molality of the solution using the mass of water in kilograms:
mass of water = 2.11 × 102 g = 211 g = 0.211 kg
molality (m) = moles of solute / mass of solvent in kg
m = 0.0647 mol / 0.211 kg = 0.307 mol/kg
Now, we need the boiling point elevation constant (Kb) for water, which is 0.512 °C/m.
Finally, we can calculate the boiling point elevation:
ΔTb = Kb * m
ΔTb = 0.512 °C/m * 0.307 mol/kg = 0.157 °C
The boiling point of the solution will be raised by approximately 0.157 °C.
b. 4.6% KCl by mass (in water)
To determine the molality of the solution, we need to find the mass of KCl and the mass of water.
Let's assume we have 100 g of the solution.
The mass of KCl would be 4.6% of 100 g, which is 4.6 g.
The mass of water would be 100 g - 4.6 g = 95.4 g.
Next, we need to convert the mass of KCl to moles using its molar mass, which is 74.55 g/mol:
moles of KCl = 4.6 g / 74.55 g/mol = 0.0617 mol
Then, we calculate the molality using the mass of water in kilograms:
mass of water = 95.4 g = 0.0954 kg
molality (m) = moles of solute / mass of solvent in kg
m = 0.0617 mol / 0.0954 kg = 0.647 mol/kg
Now, we need the boiling point elevation constant (Kb) for water.
Finally, we can calculate the boiling point elevation:
ΔTb = Kb * m
c. 0.140 m MgF2
For this solution, we are already given the molality (m) directly.
Now, we need to use the boiling point elevation constant (Kb) for water.
Finally, we can calculate the boiling point elevation:
ΔTb = Kb * m
Please note that the actual boiling point of pure water is 100 °C. To find the boiling point of the solution, you need to add the calculated boiling point elevation to this value.