Calcium chloride, CaCl2, has been used to melt ice from roadways. Given that a solution is 25% CaCl2 by mass, estimate the freezing point.
notice you get three ions per formula.
deltatemp=3*(-1.8)molality
now, molality: moles/kg solvent.
assume .75 kg solvent, then mass of solute must be 250grams, to give a twenty-five percent.
molesCaCl2=250/110 about figure it out.
molality=about 2.4/.75 you need to do this accurately.
CaCl2 = have 3 ions
delta temp = 3*(-1.858)molality = -5.57 x molality
molality = moles solute/kg solvent.
assume 0.75 kg solvent, then mass of solute must be 250 grams, to give a 25 %.
moles CaCl2 = 250/110 = 2.27 mol
molality = 2.27 mol / 0.75 kg = 3.03 m
Delta Temp = 3*(-1.858)*3.03 = -16.9 C
Thanks Bobpursley
To estimate the freezing point of a solution, we can use the concept of molality. Molality (m) is defined as the number of moles of solute per kilogram of solvent.
First, let's determine the molality of the CaCl2 solution. To do this, we need to know the molar mass of CaCl2, which is calculated as follows:
Molar mass of CaCl2 = (atomic mass of Ca) + 2 * (atomic mass of Cl)
= 40.08 g/mol + 2 * (35.45 g/mol)
= 40.08 g/mol + 70.9 g/mol
= 110.98 g/mol
Now, let's calculate the molality using the given information:
Mass percent of CaCl2 = 25%
Mass of CaCl2 solution = 1000 grams (since 25% of a 1000g solution is CaCl2)
Mass of CaCl2 = 0.25 * 1000g = 250g
Number of moles of CaCl2 = (mass of CaCl2) / (molar mass of CaCl2)
= 250g / 110.98 g/mol
≈ 2.25 mol
Now, to calculate the molality (m), we need to determine the mass of the solvent. Let's assume for simplicity that the solution weighs 1000g (which is close to the actual weight) and that it consists of 25% CaCl2 and 75% water:
Mass of solvent = Total mass - Mass of solute
= 1000g - 250g
= 750g
Now we can calculate the molality:
Molality (m) = (number of moles of solute) / (mass of solvent in kg)
= 2.25 mol / 0.75 kg
= 3.0 mol/kg
Finally, we can estimate the freezing point depression using the equation:
ΔT = Kf * m
where ΔT is the freezing point depression, Kf is the cryoscopic constant (constant for the solvent), and m is the molality.
For water, Kf is approximately 1.86 °C/m. Let's substitute the values into the equation:
ΔT = 1.86 °C/m * 3.0 mol/kg
≈ 5.58 °C
Therefore, the estimated freezing point depression of the CaCl2 solution is approximately 5.58 °C. To obtain the freezing point, we subtract this value from the normal freezing point of water, which is 0 °C:
Freezing point = 0 °C - 5.58 °C
≈ -5.58 °C
Thus, the estimated freezing point of the CaCl2 solution is approximately -5.58 °C.
To estimate the freezing point of a solution of calcium chloride in water, we need to use the colligative properties of solutions. One important colligative property is freezing point depression, which states that the freezing point of a solution is lower than that of the pure solvent.
To calculate the freezing point depression, we can use the equation:
∆Tf = Kf * m
Where:
∆Tf is the freezing point depression
Kf is the cryoscopic constant or the molal freezing point depression constant
m is the molality of the solution (moles of solute per kilogram of solvent)
First, we need to determine the molality (m) of the solution. Since the solution is 25% calcium chloride by mass, we can assume that we have 25 grams of calcium chloride in 100 grams of solution.
The molar mass of calcium chloride (CaCl2) is:
Ca = 40.08 g/mol
Cl = 2 * 35.45 g/mol = 70.90 g/mol
Total = 110.98 g/mol
To convert grams to moles, we divide the mass of calcium chloride by its molar mass:
moles of CaCl2 = 25 g / 110.98 g/mol = 0.225 mol of CaCl2
The mass of water in the solution is 75 grams (100 g - 25 g of CaCl2). To calculate the molality, we need to convert the mass of water to kilograms:
mass of water = 75 g = 0.075 kg
Now we can calculate the molality (m):
m = moles of solute / mass of solvent in kilograms
m = 0.225 mol / 0.075 kg = 3 mol/kg
Next, we need to find the cryoscopic constant (Kf) for water. The cryoscopic constant for water is 1.86 °C kg/mol.
Now we can calculate the freezing point depression (∆Tf):
∆Tf = Kf * m
∆Tf = 1.86 °C kg/mol * 3 mol/kg = 5.58 °C
Finally, to estimate the freezing point, subtract the freezing point depression from the freezing point of pure water (0 °C):
Freezing point = 0 °C - 5.58 °C = -5.58 °C
Therefore, the estimated freezing point of the calcium chloride solution is approximately -5.58 °C.