delta T = Kf*molality
Solve for molality.
molality = moles/kg solvent
Solve for moles.
moles = grams/molar mass
Solve for molar mass.
Solve for molality.
molality = moles/kg solvent
Solve for moles.
moles = grams/molar mass
Solve for molar mass.
179.8-176.7/40 = 3.1/40 = 0.0775mol
then,
0.0775*22.01g = 1.706moles
then,
0.186g/1.705mol = 0.109g/mol
then answer is 110g/mol
where have i gone wrong?
The equation for molality is m = moles/kg solvent. You MUST insert kg solvent and not grams.
Then moles = grams/molar mass or rearrange to molar mass = grams/moles. There is no "times it by 1000) here at all. The answer is molar mass, not molar mass/1000. I did make a typo at the end. The answer is 1.1 x 10^2, not 1.1 x 10^1 so 110 is correct BUT that is too many s.f. Sorry about the typo.
ΔT = Kf * m
Where:
ΔT = Change in freezing point (in degrees)
Kf = Freezing point depression constant (in degrees/m)
m = Molality of the solution (in mol/kg)
First, let's find the change in freezing point (ΔT):
ΔT = Freezing point of the pure solvent - Freezing point of the solution
The freezing point of the pure solvent is given as 179.8 degrees, and the freezing point of the solution is 176.7 degrees:
ΔT = 179.8 - 176.7
ΔT = 3.1 degrees
We know the freezing point depression constant (Kf) is 40 degrees/m. Now, we need to find the molality of the solution (m). Molality is calculated by dividing the moles of solute by the mass of the solvent in kg.
First, let's calculate the moles of solute:
moles = mass / molar mass
The mass of the organic substance is given as 0.186g. Let's assume the molar mass of the solute as M.
moles = 0.186g / M
The mass of the solvent (camphor) is given as 22.01g. We need to convert it to kg:
mass of solvent = 22.01g = 22.01g / 1000g/kg = 0.02201kg
Now, let's calculate the molality (m):
m = moles of solute / mass of solvent (in kg)
m = (0.186g / M) / 0.02201kg
m = (0.186 / M) / 0.02201
Now, we can substitute the values into the freezing point depression equation to find the molar mass (M):
ΔT = Kf * m
3.1 = 40 * [(0.186 / M) / 0.02201]
Simplifying the equation:
3.1 = (0.186 / M) * (40 / 0.02201)
3.1 = (0.186 * 40) / (M * 0.02201)
To isolate the Molar mass (M), we can rearrange the equation:
M = (0.186 * 40) / (3.1 * 0.02201)
Now, calculate the value of M:
M = (0.186 * 40) / (3.1 * 0.02201)
M ≈ 152
Therefore, the molar mass of the solute is approximately 152 g/mol.