A solution of 11.7 g of fructose in 325 g of ethanol has a boiling point of 78.59 C. The boiling point of ethanol is 78.34 C and kb for ethanol is 1.2 C/m. What is the molecular weight of fructose?
delta T = Kb*m
Solve for m = molality
m = moles/Kg solvent
Solve for moles.
moles = grams/molar mass
solve fr molar mass.
To find the molecular weight of fructose, we need to determine the change in boiling point caused by the addition of fructose to ethanol and then use the formula for boiling point elevation.
Boiling point elevation (∆Tb) is calculated using the formula:
∆Tb = Kb * m
Where:
∆Tb is the change in boiling point,
Kb is the molal boiling point elevation constant, and
m is the molality of the solution.
First, we need to calculate the molality (m) of the fructose solution. Molality is expressed in moles of solute per kilogram of solvent. In this case, the solvent is ethanol.
Moles of fructose = mass of fructose / molar mass of fructose
The mass of fructose is given as 11.7 g.
Next, we need to find the mass of ethanol in the solution. We can subtract the mass of fructose from the total mass of the solution to get the mass of ethanol:
Mass of ethanol = total mass of solution - mass of fructose
The total mass of the solution is given as 325 g.
Now we can calculate the molality:
Molality (m) = moles of fructose / mass of ethanol (in kg)
Now we will calculate the change in boiling point (∆Tb) using the given values for Kb and molality:
∆Tb = Kb * m
Substituting the known values:
∆Tb = 1.2 C/m * (moles of fructose / mass of ethanol (in kg))
Finally, we can calculate the molecular weight of fructose:
Molar mass of fructose = mass of fructose / moles of fructose
Substitute the known value for the mass of fructose, and solve for the moles of fructose:
moles of fructose = mass of fructose / molar mass of fructose
Once you have the moles of fructose, plug that value into the equation for molecular weight to calculate the answer.