calculate the freezing point of 12.0g FeCl3 in 142g water...

To calculate the freezing point of a solution, we need to use the formula for freezing point depression. Here's how you can calculate it:

Step 1: Calculate the moles of solute (FeCl3)
First, we need to calculate the moles of FeCl3. To do that, we'll use the formula:

moles = mass / molar mass

The molar mass of FeCl3 can be found in the periodic table:
Fe: 55.845 g/mol (atomic mass)
Cl: 35.453 g/mol (atomic mass)

Molar mass of FeCl3 = (1 x Fe) + (3 x Cl)
= 55.845 + (3 x 35.453)
= 162.204 g/mol

Now, let's calculate the moles of FeCl3:
moles of FeCl3 = 12.0 g / 162.204 g/mol

Step 2: Calculate the molality (moles of solute per kg of solvent)
Next, we need to calculate the molality of the solution. Molality is defined as moles of solute per kilogram of solvent:

molality = moles of solute / kg of solvent

We are given that the mass of water is 142 g. To convert it to kilograms, divide by 1000:
kg of solvent = 142 g / 1000

Now we can calculate the molality:
molality = moles of FeCl3 / kg of water

Step 3: Calculate the freezing point depression (∆Tf)
Freezing point depression is the difference between the freezing point of the pure solvent and the freezing point of the solution. The formula for freezing point depression is:

∆Tf = Kf * molality

Kf is the cryoscopic constant, which is specific to each solvent. For water, the cryoscopic constant is typically 1.86 ˚C/m.

Now, let's calculate the freezing point depression:
∆Tf = 1.86 ˚C/m * molality

Step 4: Calculate the freezing point (in ˚C)
Finally, we can calculate the freezing point of the solution using the formula:

freezing point = freezing point of pure solvent - ∆Tf

The freezing point of pure water is 0 ˚C.

Now, let's calculate the freezing point:
freezing point = 0 ˚C - ∆Tf

Plug in the calculated ∆Tf value from the previous step to obtain the freezing point of the solution.

moles FeCl3 = grams/molar mass

Solve for moles.

molality = #moles/kg solvent
Solve for molality = m

delta T = i*Kf*m
i = 4
You know m, Kf, and i, solve for delta T and subtract from the normal freezing point of water.