Question

Safrole is used as a topical antiseptic. Calculate the vapor pressure of a solution prepared by dissolving 0.75 mol of safrole in 950 g of ethanol ( molar mass = 46.07g/mol). P°ethanol = 50.0 torr at 25°C

Answer 1

Step1 moles of safrole =.75 ; Moles of ethanol=950/46.07=20.621

Step2 Mole fraction of ethanol = 20.621/21.371 =.965

Step3 Vapour pressure of solution =50.0x.965 =48.25 torr

Answer 2

Step 1:
Write the formula P = (mole fraction of solvent) X (pressure of pure solution)

Step 2:
Calculate the mole fraction of the solvent by dividing the number of moles of solvent by the total number of moles in the solution
---950 g ethanol x (1 mole of ethanol / 46.07 g of ethanol) ***units cancel = 20.62 moles of ethanol.
Next add the moles of Safrole (0.75 mol) to the moles of ethanol (20.6 mol) , this gives you the total number of moles in the solution
0.75 +20.62 = 21.37 moles total in solution so, (20.62 /21.37) = 0.965 (mole fraction of solvent)
Step 3:
Look up the vapor pressure of the pure solvent in a chemistry book or table. Luckily this was already given to us. 50 torr i don't know which units ofpressure your teacher wants your answer in but here are some conversion factors: (50 torr= 0.0667 bar) , (50 torr = 50mmHg)
Step 4:
Rewrite the formula using the values you've obtained, F
P=( 0.965) x (50 torr) = 48.25 torr (check significant digits please)