A solution was made by dissolving 62.07grams of a compound in 500g of water. The compound was not ionic. The freezing point of the solution was measured and found to be -1.86degrees celsius. The molar mass of this compound can be calculated to be?
I know I already posted this question but I couldn't find my original post so that I could have my answer checked.
I did 62.07g = mol / 500g = 0.124
0.124mol X 1000g = 124g/mol
Is this correct?
No. You have the right answer but you didn't work it right. It just happens that the numbers worked for you. Any other set of numbers (It works because m =1) and you would not get the right answer. You work it this way.
delta T = Kf*m
You know freezing point, calculate delta T from that. You know Kf. Substitute and solve for m = molality.
Then m = moles/kg solvent.
You know m and kg solvent, solve for mole.
Then moles = grams/molar mass.
You know mole and grams, solve for molar mass.
To calculate the molar mass of the compound, you need to use the freezing point depression formula. The formula can be written as:
ΔTF = KF * molality
Where ΔTF is the change in freezing point, KF is the cryoscopic constant (for water, it is -1.86 degrees Celsius/m), and molality is the molal concentration of the compound in water.
Given that the freezing point of the solution is -1.86 degrees Celsius and the mass of the compound is 62.07 grams, we need to determine the molality.
Molality (m) is defined as the number of moles of solute per kilogram of solvent. In this case, the solute is the compound, and the solvent is water.
Step 1: Calculate the molality (m):
Molality (m) = (moles of solute) / (mass of solvent in kg)
The mass of water is given as 500 g, which is 0.5 kg.
moles of solute = mass of solute / molar mass
moles of solute = 62.07 g / molar mass
molality (m) = (62.07 g / molar mass) / 0.5 kg
Step 2: Substitute the given values into the freezing point depression equation:
ΔTF = -1.86°C
KF = -1.86°C/m
molality (m) = (62.07 g / molar mass) / 0.5 kg
-1.86 = (-1.86) * [(62.07 / molar mass) / 0.5]
Simplifying the equation, you get:
1 = [(62.07 / molar mass) / 0.5]
Now, to solve for the molar mass, cross-multiply and rearrange the equation:
(62.07 / molar mass) = 0.5
molar mass = 62.07 / 0.5
molar mass = 124.14 g/mol
So, the molar mass of the compound is approximately 124.14 g/mol.
Therefore, your initial calculation was correct. The molar mass of the compound is 124.14 g/mol.