I forgot to post this one with the other
What is the freezing point of a solution containing 4.0 Mol of sodium chloride in 1200 grams of water? (kf for water is 1.86 C/M)
I don't really want the whole answer, just where I would plug in the numbers. I keep forgetting what formula to use.
It is best to post questions separately. Better chance of getting both of them worked.
m = moles/kg solvent
solve for m since you have moles and g solvent.
Then delta T = i*Kf*m
i for NaCl = 2.
m = 4.0/1200 = 300
T = 2*1.86 c/m*300 = 1116
Nope. m = moles/Kg solvent. That is 1.2 and not 1200
and T is not the same as delta T. delta T is how much the freezing point has changed. The normal freezing point of water is 0 degrees C so detla T will decrease it by that much. I get something like -12.4 C.
To find the freezing point of a solution, you can use the formula:
deltaT = (kf)(m)(i)
Where:
- deltaT is the change in freezing point
- kf is the freezing point depression constant for the solvent (in this case, water)
- m is the molality of the solute (in this case, sodium chloride)
- i is the van't Hoff factor, which represents the number of particles formed when the solute dissociates in the solvent
In this case, the sodium chloride (NaCl) will dissociate into two ions (Na+ and Cl-), so the van't Hoff factor (i) is 2.
You have been given:
- kf for water = 1.86 °C/molal
- m (molality) = 4.0 mol of NaCl
- mass of water = 1200 grams
To find where to plug in the numbers, let's go step by step:
1. Convert the mass of water from grams to kilograms:
mass of water = 1200 grams = 1.20 kilograms
2. Calculate the molality (m) by dividing the moles of solute by the mass of solvent in kilograms:
m = (moles of solute) / (mass of solvent in kg)
m = 4.0 mol / 1.20 kg
3. Plug in the values of kf, m, and i into the formula:
deltaT = (1.86 °C/molal) * (4.0 mol / 1.20 kg) * 2
Now, you can calculate the freezing point depression deltaT by plugging in these values into the formula. I'll leave it to you to perform the calculation and get the final result.