Compute the vapor pressure of water above a solution formed by dissolving 25.00 grams of magnesium sulfate, MgSO4 (MM=120.3) in 95.00 grams of water at 338K. The vapor pressure of pure water at 338K is 188.0 torr.
I took 95.00g H20 divided by 18.0g. which gave me moles for top. I than took those moles and added them to 25.0 divided by 120.3. I than took 5.277 mol H20 divided by 5.4856total moles time 188.0 torr. which i than got 180.88 vapor pressure of water.
•Find the moles of MgSO4 by dividing 95.00g by the formula mass of MgSO4.
•Multiply the moles of MgSO4 by 3 ions / mole to get the moles of ions in solution.
•Convert 95g of H2O to moles.
•Add moles of ions to moles of H2O to get total moles.
•The moles fraction of H2O is:
X(H2O) = (moles H2O)/(total moles)
•P(solution) = X(H2O)P(H2O)
•P(solution) = X(H2O)(188 mm) = ?
To compute the vapor pressure of water above the solution, you need to use the concept of Raoult's law. Raoult's law states that the vapor pressure of a solvent (in this case, water) above a solution is proportional to the mole fraction of the solvent in the solution.
Let's break down the calculation step by step:
1. Calculate the number of moles of water:
Moles of water = mass of water / molar mass of water
Moles of water = 95.00 g / 18.0 g/mol
Moles of water = 5.277 mol
2. Calculate the total moles in the solution:
Total moles = moles of water + moles of solute
Moles of solute = mass of solute / molar mass of solute
Moles of solute = 25.00 g / 120.3 g/mol
Moles of solute = 0.2076 mol
Total moles = 5.277 mol + 0.2076 mol
Total moles = 5.4846 mol
3. Calculate the mole fraction of water:
Mole fraction of water = moles of water / total moles
Mole fraction of water = 5.277 mol / 5.4846 mol
Mole fraction of water = 0.961
4. Apply Raoult's law to calculate the vapor pressure of water:
Vapor pressure of water = mole fraction of water * pure vapor pressure of water
Vapor pressure of water = 0.961 * 188.0 torr
Vapor pressure of water = 180.9688 torr (rounded to four decimal places)
Therefore, the vapor pressure of water above the solution is approximately 180.9688 torr.