What is the vapor pressure in mm Hg of a solution prepared by dissolving 18.3 g of NaCl in 500.0g H20 at 70 °C. (The v.p. of water at 70°C is 233.7 mm Hg.)
To calculate the vapor pressure of the solution, we need to use Raoult's law. According to Raoult's law, the vapor pressure of a solution is equal to the mole fraction of the solvent multiplied by the vapor pressure of the pure solvent.
First, let's calculate the mole fraction of water:
Moles of water = mass of water / molar mass of water
Moles of water = 500.0 g / 18.015 g/mol
Moles of water = 27.754 mol
Moles of NaCl = mass of NaCl / molar mass of NaCl
Moles of NaCl = 18.3 g / 58.44 g/mol
Moles of NaCl = 0.313 mol
The total moles of solute and solvent = 27.754 + 0.313 = 28.067 mol
The mole fraction of water = moles of water / total moles
Mole fraction of water = 27.754 mol / 28.067 mol
Mole fraction of water = 0.989
Now, we can calculate the vapor pressure of the solution using Raoult's law:
Vapor pressure of solution = mole fraction of water * vapor pressure of pure water
Vapor pressure of solution = 0.989 * 233.7 mm Hg
Vapor pressure of solution = 231.1063 mm Hg
Therefore, the vapor pressure in mm Hg of the solution is approximately 231.1063 mm Hg.