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Nevermind i got the answer(:
It is 135 Torr
A solution contains naphthalene (C10H8) dissolved in hexane (C6H14) at a concentration of 15.00% naphthalene by mass. Calculate the vapor pressure at 25 ∘C of hexane above the solution. The vapor pressure of pure hexane at 25 ∘C is 151 torr. I keep getting 168 torr but it says I am wrong please help me understand what I am doing wrong.
Kaitlyn
answered10 years ago
Explain Bot
answered11 months ago
To calculate the vapor pressure of hexane above the solution, you need to apply Raoult's law, which states that the vapor pressure of a component in an ideal solution is directly proportional to its mole fraction in the solution.
First, let's find the mole fraction of hexane in the solution:
1. Calculate the mole fraction of naphthalene (C10H8):
- Determine the molar mass of C10H8:
M(C10H8) = 10*(12.01 g/mol) + 8*(1.01 g/mol) = 128.18 g/mol
- Calculate the moles of naphthalene:
Moles of C10H8 = (15.00 g C10H8) / (128.18 g/mol) = 0.1170 mol C10H8
2. Calculate the mass of hexane (C6H14) in the solution:
- Mass of hexane = 100 g - 15.00 g = 85.00 g
3. Calculate the moles of hexane (C6H14):
Moles of C6H14 = (85.00 g C6H14) / (86.18 g/mol) = 0.9854 mol C6H14
4. Calculate the mole fraction of hexane:
Mole fraction of C6H14 = Moles of C6H14 / (Moles of C10H8 + Moles of C6H14)
= 0.9854 / (0.9854 + 0.1170)
≈ 0.894
Now that we have the mole fraction of hexane, we can calculate the vapor pressure of hexane above the solution using Raoult's law:
Vapor pressure of hexane above the solution = Mole fraction of hexane * Vapor pressure of pure hexane
Vapor pressure of hexane above the solution = 0.894 * 151 torr
= 134.94 torr
Therefore, the vapor pressure of hexane above the solution at 25 °C is approximately 134.94 torr.