When 9.18 g of a soluble nonelectrolyte was dissolved in 100 g of ethanol at 78.4°C, the vapor pressure of the solution was measured to be 740 mm Hg.
a)
What are the mole fractions of ethanol and solute?
b)
What is the molecular weight of the solute?
I don't know the vapor pressure of ethanol at 78.4 C but you can look that up. I will assume it is 760 mm since I know that is close to the boiling point of ethanol.
Psoln = Xsolvent*Posolvent
Solve for Xsolvent.
Then 1-Xsolvent = Xsolute which is part a.
Then Xsolute = (moles solute/moles solute + moles solvent).
You know moles solvent = 100 g/molar mass ethanol. Substitute into the Xsolute equation above and solve for moles solute.
Then n(solute) = grams solute/molar mass
You have n and g, solve for molar mass, which is part b.
To find the mole fractions of ethanol and the solute, we first need to calculate the number of moles of each component.
a) To calculate the mole fraction of ethanol, we can use the formula:
Mole fraction of ethanol = moles of ethanol / total moles
First, let's find the moles of ethanol. We know the mass of ethanol is 100 g, so we need to convert this to moles using the molecular weight of ethanol.
The molecular weight of ethanol (C2H5OH) can be calculated as follows:
Atomic weight of carbon (C) = 12.01 g/mol
Atomic weight of hydrogen (H) = 1.01 g/mol (there are 6 hydrogen atoms in ethanol)
Atomic weight of oxygen (O) = 16.00 g/mol
The molecular weight of ethanol = (12.01 x 2) + (1.01 x 6) + 16.00 = 46.07 g/mol
Now we can calculate the moles of ethanol:
moles of ethanol = mass of ethanol / molecular weight of ethanol
moles of ethanol = 100 g / 46.07 g/mol
Next, let's find the moles of the solute. We know the mass of the solute is 9.18 g, but we don't have the molecular weight of the solute given. Therefore, we cannot directly calculate the moles of the solute without additional information.
b) To find the molecular weight of the solute, we need to know the identity of the solute. Without this information, we cannot calculate the molecular weight or provide an accurate answer.
In summary,
a) We can calculate the mole fraction of ethanol using the known mass of ethanol and the molecular weight of ethanol.
b) We cannot calculate the molecular weight of the solute without additional information.