The boiling point elevation of a solution consisting of 2.12 g of a nonvolatile solute in 97.4 g of benzene is 0.6602 oC. What is the molecular weight of the unknown solute?
i have no idea how to solve this question
delta T = Kf*molality
delta T = 0.660
Look up Kf for benzene (the freezing point depression constant for benzene which probably is in your text).
Calculate molality.
Then
Kg solvent x molality x molar mass = grams. Solve for molar mass.
thanks
To solve this question, we can use the concept of boiling point elevation, which relates the change in boiling point to the molality of a solute in a solution.
The formula for boiling point elevation is:
ΔTb = Kb * m
Where:
ΔTb is the boiling point elevation
Kb is the molal boiling point elevation constant of the solvent (benzene in this case)
m is the molality of the solute in the solution
In this case, we are given the following information:
ΔTb = 0.6602 oC
mass of solute (m) = 2.12 g
mass of solvent = 97.4 g
First, we need to calculate the molality of the solute using the formula:
molality (m) = moles of solute / mass of solvent (in kg)
To find the moles of solute, we need to use the molecular weight of the solute (Mw).
moles of solute = mass of solute / molecular weight (Mw)
Since we already have the mass of the solute, we can rearrange the formula to solve for Mw:
Mw = mass of solute / moles of solute
To find moles of solute, we can use the formula:
moles of solute = molality * mass of solvent (in kg)
Now, let's plug in the given values and solve the problem step by step:
Step 1: Convert the mass of solvent from grams to kilograms:
mass of solvent = 97.4 g = 97.4 / 1000 kg = 0.0974 kg
Step 2: Calculate the molality of the solute:
m = moles of solute / mass of solvent (in kg)
Step 3: Rearrange the formula to solve for moles of solute:
moles of solute = m * mass of solvent (in kg)
Step 4: Calculate the molecular weight of the solute:
Mw = mass of solute / moles of solute
By following these steps and using the provided values, you should be able to calculate the molecular weight of the unknown solute.