Determine the freezing point of an aqueous solution containing 10.50 g of magnesium bromide in 200.0 g of water.
mols MgBr2 = grams/molar mass = ?
m solution = mols MgBr2/kg solution.
Then delta T = i*Kf*m
i for MgBr2 = 3
You know Kf and m, solve for delta T, then subtract from zero to find new freezing point.
-1.59 degrees Celsius
To determine the freezing point of the aqueous solution, you need to use the formula ΔTf = Kf * m, where ΔTf is the change in freezing point, Kf is the cryoscopic constant for water (-1.86°C/m), and m is the molality of the solution.
First, calculate the molality of the solution using the formula:
molality (m) = moles of solute / mass of solvent (in kg)
1. Calculate the moles of magnesium bromide (MgBr2):
The molar mass of MgBr2 = 24.31 g/mol (for Mg) + 2 * (79.90 g/mol) (for 2Br) = 184.31 g/mol
moles of MgBr2 = mass of MgBr2 / molar mass of MgBr2
Given that the mass of MgBr2 is 10.50 g, we can calculate:
moles of MgBr2 = 10.50 g / 184.31 g/mol
2. Calculate the mass of water in kg:
Given that the mass of water is 200.0 g and the density of water is approximately 1 g/mL, we have 200.0 g * (1 mL / 1000 g) = 0.200 kg
3. Calculate the molality:
molality (m) = moles of solute / mass of solvent (in kg)
molality (m) = moles of MgBr2 / mass of water (in kg)
Now we have all the required values to calculate the molality.
4. Substitute the values into the freezing point depression equation:
ΔTf = Kf * m
Given that Kf for water is -1.86 °C/m, substitute the calculated molality (m) into the equation:
ΔTf = (-1.86 °C/m) * molality
This calculated ΔTf represents the change in freezing point of the solution compared to the pure solvent. To find the freezing point of the solution, subtract ΔTf from the normal freezing point of water (0°C).
5. Calculate the freezing point of the solution:
Freezing point of solution = 0°C - ΔTf
Now you can calculate the freezing point of the solution using the given data and the steps above.