Multiple Choice
What is the freezing point (in degrees Celsius) of 3.28 kg of water if it contains 170.5 g of CaBr2? The freezing point depression constant for water is 1.86 °C/m and the molar mass of CaBr2 is 199.89 g/mol.
14. Solutions
Freezing Point Depression
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What is the freezing point of a solution that contains 50.0 g of NaNO₃ in 200.0 g of water, given that the molal freezing point depression constant (Kf) for water is 1.86 °C/m?
A
-0.93 °C
B
0.00 °C
C
-1.86 °C
D
-3.72 °C
Verified step by step guidance1
First, calculate the molality of the solution. Molality (m) is defined as the number of moles of solute per kilogram of solvent. Begin by finding the number of moles of NaNO₃. Use the formula: . The molar mass of NaNO₃ is approximately 85 g/mol.
Next, calculate the molality using the formula: . Convert the mass of water from grams to kilograms by dividing by 1000.
Now, apply the freezing point depression formula: , where is the change in freezing point, is the freezing point depression constant, and is the molality.
Calculate the change in freezing point using the values obtained for molality and the given value of 1.86 °C/m.
Finally, determine the new freezing point of the solution by subtracting the change in freezing point from the normal freezing point of water, which is 0.00 °C.
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