Raoult's Law - How To Calculate The Vapor Pressure of a Solution

This paragraph introduces Raoult's law, which is used to calculate the vapor pressure of a solution. The equation states that the vapor pressure of a solution is the product of the mole fraction of the solvent and the vapor pressure of the solvent. The law implies that adding a non-volatile solute to a solvent will decrease the vapor pressure of the solution. An example is provided where the vapor pressure of a glucose-water solution is calculated, demonstrating how the vapor pressure is less than that of pure water. The process involves calculating the moles of water and glucose, determining the mole fraction of water, and then using Raoult's law to find the vapor pressure of the solution.

This paragraph extends the discussion on Raoult's law to include solutions with ionic solutes, such as calcium chloride in water. The key difference highlighted is that the total moles of ions in the solution must be considered, not just the moles of the ionic compound itself. The example calculates the moles of water and calcium chloride, converts the moles of calcium chloride to the moles of ions, and then calculates the mole fraction of water. Using Raoult's law, the vapor pressure of the solution is determined, showing how it is affected by the presence of ionic solute particles.

The final paragraph focuses on using Raoult's law to determine the amount of glucose needed to achieve a specific vapor pressure in a water solution. Given the vapor pressure of water at 40 degrees Celsius and the desired vapor pressure of the solution, the mole fraction of water is calculated. This leads to determining the moles of water and subsequently the moles of glucose required. The process involves algebraic manipulation to solve for the moles of glucose and then converting these moles to grams, ultimately providing the mass of glucose needed to create a solution with the desired vapor pressure.