The vapor pressure of diethyl ether is 463.57 mm Hg at 25 degrees celsius. How many grams of aspirin C9H8O4, a non volatile nonelectrolyte (mw=180.1g/mol), must be added to 216.7g of ether to reduce the vapor pressure to 453.74 mm Hg.
Ether=74.12g/mol
This question is similar to the other one that I posted. Do I first have to convert to moles for both?
Yes for ether. You don't know grams aspirin so you can't calculate moles aspirin.
Subtract normal vp ether - vp ether desired, plug into
pether = Xether*Po ether and solve for Xether.
Then find Xaspirin (it's 1.000 - Xether) and from that grams aspirin.
It's just the reverse of what you did in the other problem.
so I did 463.57 - 453.74 = 7.600
Then I found moles of ether to be 4.0313.
I do not understand the next step to find Xether.
Yes, in order to solve this problem, you will need to convert the given masses of diethyl ether and aspirin to moles. This will allow you to apply the principles of stoichiometry to find the amount of aspirin needed to lower the vapor pressure.
To convert grams to moles, you can use the molar mass of the substances involved. The molar mass of diethyl ether (C4H10O) is 74.12 g/mol, and the molar mass of aspirin (C9H8O4) is 180.1 g/mol.
First, let's calculate the number of moles of diethyl ether present in 216.7 g:
moles of diethyl ether = mass of diethyl ether / molar mass of diethyl ether
= 216.7 g / 74.12 g/mol
= 2.9241 mol
Next, we need to use the vapor pressure lowering formula, which is based on Raoult's Law:
ΔP = Xsolute × P°solute
Where ΔP denotes the change in vapor pressure, Xsolute represents the mole fraction of the solute (aspirin), and P°solute is the vapor pressure of the pure solute.
We are given that the initial vapor pressure of diethyl ether is 463.57 mm Hg, and we want to reduce it to 453.74 mm Hg. Therefore, the change in vapor pressure, ΔP, is:
ΔP = 453.74 mm Hg - 463.57 mm Hg
= -9.83 mm Hg (note the negative sign indicating a decrease)
Now, we can rearrange the formula to solve for the mole fraction of the solute:
Xsolute = ΔP / P°solute
The mole fraction can also be expressed as:
Xsolute = moles of solute / (moles of solute + moles of solvent)
Since the aspirin is non-volatile and nonelectrolyte, its vapor pressure is considered negligible.
By rearranging the equations, we get:
moles of solute = Xsolute × (moles of solute + moles of solvent)
We already have the moles of the solvent (diethyl ether) calculated earlier, which is 2.9241 mol. Now, we can substitute the values into the equation to find the moles of aspirin:
moles of aspirin = Xsolute × (moles of aspirin + 2.9241 mol)
Finally, we can convert the moles of aspirin back to grams using the molar mass of aspirin:
mass of aspirin = moles of aspirin × molar mass of aspirin
Substitute the given values into the equations, and you can solve for the mass of aspirin required to lower the vapor pressure.