Answer:
The amount of sucrose that must be added is 1.66 moles
Explanation:
Colligative property of lowering vapor pressure has this formula:
Vapor pressure of pure solvent (P°) - Vapor pressure of solution = P° . Xm
We have both vapor pressure (pure solvent and solution9, so let's determine the ΔP
ΔP = 92.6 Torr - 72 Torr = 20.6 Torr
Let's add the data in the formula
20.6 Torr = 92.6 Torr . Xm
Xm = Mole fraction of solute → (mol of solute/ mol of solute + mol of solvent)
Mol of solvent = 5.83 mol (data from the problem)
Therefore Xm = 20.6 Torr / 92.6 Torr → 0.222
Let's find out the moles of solute (our unknown value)
0.22 = moles of solute / moles of solute + 5.83 moles of solvent
0.222 (moles of solute + 5.83 moles of solvent) = moles of solute
0.222 moles of solute + 1.29 moles of solvent = moles of solute
1.29 moles of solvent = moles of solute - 0.222 moles of solute
1.29 moles = 0.778 moles of solute
1.29 / 0.778 = moles of solute → 1.66 moles
