The normal boiling point of ethanol is 78.4°C. When 9.16 g of a soluble nonelectrolyte was dissolved in 100. g of ethanol, the vapor pressure of the solution at that temperature was 7.40 102 Torr.
(a) What are the mole fractions of ethanol and solute?
(b) What is the molar mass of the solute?
We. came. here. for. the. answer. not. for. you. to. tell. us. to. do. it.
The vapor pressure is actually 7.40 x 10^2
The vapor pressure of ethanol (any liquid at its boiling point) is 760 torr. So
Psoln = Xethanol*Poethanol.
Xethanol = P/Po = 740/760 = ??
Xethanol + Xsolute = 1
(b). You know 100 g ethanol. Change to moles ethanol.
nethanol/(nethanol+nsolute) = Xethanol (from a part).
Solve for nsolute(moles solute).
Then moles = grams/molar mass. Solve for molar mass.
Post your work if you get stuck.
Thanks for the help DrBob
I forgot the pressure of any liquid at boiling point
To find the mole fractions of ethanol and solute, we need to know the vapor pressure of pure ethanol at its normal boiling point and the vapor pressure of the solution.
(a) To find the mole fractions of ethanol and solute, we can use the Raoult's law equation:
Psolution = Xethanol * Pethanol
Where,
Psolution = vapor pressure of the solution
Xethanol = mole fraction of ethanol
Pethanol = vapor pressure of pure ethanol
We know that the vapor pressure of pure ethanol at its normal boiling point is 78.4°C. This means that the vapor pressure of pure ethanol at 78.4°C is also 1 atm, or 760 Torr.
Using the given information, the vapor pressure of the solution is 7.40 * 10^2 Torr.
Now we can rearrange the Raoult's law equation to solve for Xethanol:
Xethanol = Psolution / Pethanol
Xethanol = 7.40 * 10^2 Torr / 760 Torr
Xethanol ≈ 0.974
To find the mole fraction of the solute, we can use the fact that the sum of mole fractions in a solution is always equal to 1:
Xsolute = 1 - Xethanol
Xsolute = 1 - 0.974
Xsolute ≈ 0.026
Therefore, the mole fractions of ethanol and solute are approximately 0.974 and 0.026, respectively.
(b) To find the molar mass of the solute, we can use the formula:
Molar mass = (Mass of solute / Moles of solute)
We know the mass of the solute is 9.16 g, but we need to find the moles of the solute.
To find the moles of solute, we can use the formula:
Moles = Mass / Molar mass
We know the mass of the solute (9.16 g), so we now need to find the molar mass of the solute.
To find the molar mass of the solute, we can use the formula:
Molar mass = (Mass of solute / Moles of solute)
We know the mass of the solute is 9.16 g, but we need to find the moles of the solute.
To find the moles of solute, we can use the formula:
Moles = Mass / Molar mass
Therefore, to find the molar mass of the solute, we can rearrange the formula as:
Molar mass = Mass of solute / Moles of solute
Molar mass = 9.16 g / (0.026 mol)
Molar mass ≈ 352.31 g/mol
Therefore, the molar mass of the solute is approximately 352.31 g/mol.