A solution of sodium chloride in water has a vapor pressure of 18.3 torr at 25°C. What is the mole fraction of NaCl in this solution?
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What would be the vapor pressure of this solution at 45°C? The vapor pressure of pure water is 23.8 torr at 25°C and 71.9 torr at 45°C.
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For 1,
delta Psolution = Xsolute*Posolvent
Look up vp H2O at 25 C, that is Po.
Take the difference between that and 18.3 to obtain delta P.
To find the mole fraction of NaCl in the solution, we can use Raoult's Law, which states that the vapor pressure of a solution is directly proportional to the mole fraction of the solute in the solution.
Given:
Vapor pressure of the solution at 25°C = 18.3 torr
To find the mole fraction of NaCl, we need the vapor pressure of pure water at 25°C. Given that the vapor pressure of pure water at 25°C is 23.8 torr, we can use the following equation:
Vapor pressure of solute (NaCl) in the solution = Mole fraction of solute (NaCl) * Vapor pressure of solvent (water)
Since we know the vapor pressure of the solvent (water) and the vapor pressure of the solution, we can rearrange the equation to solve for the mole fraction of the solute (NaCl):
Mole fraction of NaCl = Vapor pressure of the solution / Vapor pressure of water
Substituting the given values:
Mole fraction of NaCl = 18.3 torr / 23.8 torr
Calculating this gives us the mole fraction of NaCl in the solution.
Once we have the mole fraction of NaCl at 25°C, we can use Raoult's Law again to find the vapor pressure of the solution at 45°C. The equation for Raoult's Law is:
Vapor pressure of solution at a different temperature = Mole fraction of solute * Vapor pressure of solvent at that temperature
Substituting the known values into the equation, we can calculate the vapor pressure of the solution at 45°C.